The pathology of laryngeal hemiplegia in the horse : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Veterinary Science at Massey University

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(2) T H E PAT HOLOGY OF LARYNGEAL HEMIPLEGIA. I N THE HORSE. A THESIS PRESENTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSPHY IN VETERINARY SCIENCE AT MASSEY UNIVERSITY. JENNIFER IRENE CAHILL s.v.sc.. 1985.

(3) T H E PAT HOLOGY OF LARYNGEAL HEMIPLEGIA. IN T H E HORSE. VOLUME I.

(4) iii. ABSTRACT. A. r ev i ew. o f ·the. l i terature on equ i n e. i nd i c a t ed. that. order. d e f ine. to. proce s s e s . we re. i nve s t igat i on s. more. Th i s. S t a ndardbred four. f u rther. c le a r l y. the. i nve s t i ga t ion. a nd. f ou rteen. c l i n i ca l l y. l a ryngea l h em i p l e g i a we re. unde r l y i ng. wa s. with. hor s e s,. l aryngea l. in. pathoge n i c. under taken. Thoroughbred. a f f e c ted. warranted , on of. one wh i c h. hemi p l eg i a ,. f ive subcl i n i ca l ly a f f ec ted and s i x we r e apparen t l y norma l . The i r i ned. l e f t and r i ght in. deta i l ,. as. recurrent laryngeal nerves were exam­ were. c l i nica lly. a f f ec ted. t e chniques. we re. h indl imb. a n ima l s .. empl oyed ,. A. nerves. f r om. var i ety. of. i n c lud ing. m i c r o s c opy of re s i n embedded nerve , eva l u a ted. wa s. l a ryng e a l mu s c l e s , wer e. the. h i s tolog i ca l and. e le ct ron. and s ing l e tea s ed f i br e S ome. s ta t i s t i ca l ly .. i n t r in s i c. and the e xtenh o � d i g it o � um l o n g u h mu s c l e. i nve st igated .. recurrent. of. Quanti t a t i ve data obta ined from the s e i nve s t ­. prepa ra t ions . i g a t i on s. l i ght. two. I n add i t i on ,. l aryngea l. nerve. the motor nuc l e u s o f. f i bre s ,. the. the. n u cl e u h am!i g u u h. ,. a nd long centra l nerve f i bre trac t s were exami ned . The. recurrent i ng. l ong. p r i ma r y than. of. as. a. has. equ i n e. a. d i s ta l. the. left. prev i ou s ly. been. d i sease. it. of. of. a genera l i s ed neuropa tho l og i c a l proce s s a f f e c t ­. and. l arge. d i ameter. nerve. f ibre s wa s. f ound .. The. s i te of the l e s ion wa s shown to be the axon r a t h e r. the. s tr a ted . f ib r e s. nerve ,. l aryngea l. cons ide red ,. b e i ng. than. Rather. a xo nopa thy .. neuropa thy. charac te r i s t i c. is. hem i p l e g i a. l a ryngea l. the. that. demon s t r a ted. results. mye l i n As. in. i nvolvement wa s fou nd .. sheath .. we l l. the of. as. the. d i sease l ong. D i stal. a xona l. i nvolvement proce s s ,. f i bres. of. t he. s ome. a trophy wa s d emon ­ of. pe r i pher a l ev i dence. centra l. n erve. for. nervou s. the. s y s tem.

(5) iv. In. addi t ion ,. with. i nve s t i g a t i o n. s t r ingha l t ,. per f o rmed wa s. an. on. another. one. nervous. anima l .. It. a l so a di s ta l axonopa thy ,. ence s. f rom. I t wa s. i d i opath i c. an acute. of. condi t ion o f hor se s ,. wa s. d emon s t r a t ed. t ha t. wa s this. a l t hough a number o f di f f e r ­. l a ryngea l. rather. the pathology a s s ociated. than a. hem i plegia. were. chron i c proce s s ,. obs e rved . a nd l acked. any i nvolvemen t o f centra l f i bre s . I n concl us ion , pos t u lated. cau s e s. be d i s mi s s ed , d i s ta l. i t wa s sugge s t ed that a number o f previ ou s ly for. s uch. as. the. mo s t. l aryngea l. hem ip le g i a. cou ld. on the ba s i s of the f i nd ing of a gene ra l i s ed. axonopa thy .. mechan ica l. equ ine. d amage. Th i s to. the. i n c l uded left. recur rent. stretch or compre s s ion . l ikely. ae t i o l ogy. those. wh ich. l a ryngea l. I n l i ght of. und e r l y i ng. s ugg e s ted. the. nerve ,. the f i nd i ng s , pathology. of. equ i n e lar y nge a l hem i p l e g i a wa s c on s i dered t o b e ·an a c q u i red or. i nheri ted. in. the. axon ,. metabol i c wi th. the. d e f ect. a f f ec t i ng. r e s u l tant. ene rgy. i nab i l i t y t o. p rodu c t i on s upport. d i s t a l area s o f l ong , large d iame ter nerve f i br e s .. the.

(6) V. ACKNOWLEDGEMENTS. The author w i shes to tha nk the Comm i t tee of the New Z e a la nd Equ i n e R e s earch Found a t i on. for. the. f inanc i a l s upport whi ch. made th i s i nve s t i ga t i on pos s i bl e . The. a s s i s t a nce. of. many. peop l e ,. dur i ng exper imenta l stud i e s. a nd prepa ra t i on o f th i s the s i s i s grate fu l ly a cknowledged . Dr. Brian. Goulden. for. conti nued e ncouragement. a nd guidance. throughou t the cou r s e o f th i s work . Dr Robert Jo l ly for i n t e r e s t and adv i c e . Dr. Mar t i n. P o l lock ,. the. Clinica l. for. help. S t eve. Neuro l ogy. w i th. the. A l lpr e s s. Unit. of. t e c hn i q u e s. a nd. the. and. other. Otago. membe r s. Med i ca l. s t a t i st i ca l. of. School. a na l y s e s. of. pe r i phe r a l nerve inve s t i ga t i on . P r o f e s sor. Ron. Munford. for. a s s i s tance. in. the. d ev e l opme n t. o f computer programm e s for s t a t i s t i c a l ana l y s e s . P a t Davey for expe r t techn i ca l a s s i s tance . Doug. Hopcroft. a nd. R a ymond. Bennett. f or. adv i ce. on. e le ct r o n. m i c ros copy , and the produ c t ion of e l e c t�mi c rograph s . Member s who. of. the. prov i ded. Department a s s i s tance. o f Ve ter i nary C l i n i c a l d u r i ng. the. surg i ca l. S e rv i c e s. c o l l e c t i on. o f nerve sampl e s . K e e s Korndo r f f e r for the i l l u s t ra t i on s . Tom Law f or the photograph s . Ve ron i ca F i e l d s end for typing of the f i na l manu s c r ipt ..

(7) vi. TABLE OF CONTENTS. PAGE f. ABST�CT . ,. iii. ACKNOWL�DGEMENTS. V. TABLE OF CONTENT S. vi. L I S T O F TABLES. xii. L I S T OF F IGURES. xvi. PART 1 :. I NTRODUCTION. 1. I n t rodu c t ion. 1. Ana tomy. 3. Pa t ho l ogy. 3. Aet i o l ogy. 11. Mecha n i c a l Cau s e s. 12. B i omechan i c a l theory of s t re t ch t o the l e f t recurrent l aryng e a l nerve. 12. Compre s s ion of t h e recurrent laryngeal nerve i n the area o f the a o r t i c arch. 1 4. Ba c t e r i a l and V i r a l Age n t s. 17. P l a n t a nd Chemi ca l I ntox i ca t i on s. 19. Pl a n t i ntox i c a t i o n s. 19. Chemi ca l intox i ca t ion s. 20. Lead po i s o n i n g. 20. V i t am i n Def i c ie n c i e s. 21. F a c t o r s Pred i s po s i n g to Equ ine La ryngea l Hemi p l egia. 24. Breed. 24. Hered i t y. 25. S i ze Sex. 28 28. Management. 29. Conforma t i o n. 29. C l ima te a nd geography. 29. Cont ' d.

(8) vii. TABLE OF CONTENTS CONTINUED : PAGE PART I I :. PERIPHERAL NERVE PATHOLOGY IN EQUINE LARYNGEAL HEMIPLEGIA. 1. •. P e r iphera l N erve and I t s React i on to D i s e a s e. 31 31. I nt roduct i on. 31. Pa tho l ogy of Pe r i ph e r a l Nerve. 33. C l a s s i f i ca t i o n o f patho l ogy. 33. W a l l e r ian degenerat ion. 33. Axona l degene r a t i on. 34. Segmental d emye l i na t i on. 36. Other patho l o g i c a l a l t e ra t i on s in p eripheral nerve Degene ra t i o n and regenera t i on Degener a t i n g mye l i na t ed f ib r e s. 38 38 . 38. Axonal swe l l i ng s. 39. U l t r a s t ru c t u r a l axona l a l tera t i on s. 40. Axon-Sc hwann ce l l networks. 41. Axonal regenera t ion. 42. Mast ce l l s. 44. The Schwann ce l l i n hea l t h and d i s e a s e. 44. Secondary demye l in a t i on. 46. "On ion bu lbs". 49. Col lagen pock e t s. 51. I n ternode l engths. 51. R e l a t ionsh i p o f a xona l ca l ibre a nd mye lin sheath t h i ckne s s. 53. A g e r e l a t ed change s i n per i ph e r a l nerve. 54. R o l e of axopl a sm i c transport i n per i pheral neuropa thi e s Approach to I n v e s ti ga t i ng a Per iphe r a l Neuropathy. 57 59. Samp l i ng. 60. F i xa t ion. 60. L i gh t m i c ros copy. 61. T e a s ed f i br e prepara t i on s. 62. Ele c tron mi c r o s c opy. 64. Morphometry. 65 Cont'd.

(9) viii. TABL E OF CONTENTS CONTINUED : PAGE F i bre d i ameter d i s t r i bu t ions. 66. Internode l e ngths. 67. The re l a t i o n s h i p between axonal c a l ibre and mye l in sheath t h i ckn e s s. 68. 2 . M a te r i a l s a n d Methods. 69. Exper imenta l Anima l s. 69. S a mp l i n g Method f or Recurrent Laryngea l and Vag a l Nerves. 70. Proce s s ing for T e a s ed Fibre Prepa r a t i on s. 74. Tea s ed F i bre Preparat i on. 75. Proce s s ing for L i gh t and E lec tron M i c r o s copy. 77. Prepa ra t i on of Sect ions for L i ght M i c ro s copy. 78. E l e c t ron M i cros copy. 79. 3 . Results. 80. L i g h t Mi croscopy. 80. Morpho logy. 80. Morphome try. 84 89. Te a sed F i bre Prepar a t i on s Morpho logy. 89. Morphome try. 93 95. E l e c t ron M i c r o s copy Morpho logy. 95. Morphome try. 99. 4. D i s c u s s i on. 1 00 1 00. L i g h t M i c ros copy Morpho logy. 1 00 1 03. Morphometry. 1 07. T e a s ed F i bre Prepar a t ions Morpho logy. 1 07. Morphometry. 110. E le c t ron M i c r o s copy. 112. Morpho logy. 112. Morphometry. 1 14 116. Sui!lmary (". '. '. ,.

(10) ix. TABLE OF CONTENTS CONTINUED : PAGE MUSCLE PATHOLOGY IN EQU INE LARYNGEAL. PAR T I I I :. HEM I PLEGIA. 119. I n t roduc tion. 119. M a t e ria l s and M e t hods. 1 20. Re s u l t s. 1 21. c�i c o th y � o i d e u � mu s c l e s. L e f t c�i c o a � y t e n o ideu� Late� a Li� mu s c l e. 1 25 1 25. Right c�i c o a � y t e n o ideu� Late� aLi� mu s c le. 1 25. L e f t c�i c o a � y t e n o ideu� d o � � a Li � mu s c l e. 1 25. Right c�i c o a � y t e n o i d e u � d o � � aLi� m u s c l e. 1 26. Exten � o � digit o � um L o n g u � mu s c l e. 1 26 1 26. Di s cu s sion PART IV :. THE CENTRAL NERVOUS SYSTEM I N EQUINE LARYNGEAL HEMIPLEGIA. I n troduction Nu cLe u � a m t i g u u �. Long spina l t r a c t s Ma teria l s and M et hod s Nu cLe u� am£.i g u u�. Long spina l t r a c t s R e su l t s Nu cLeu� am£.i g u u�. Long s pina l t r a c t s Di s cu s sion. 1 29 1 29 1 30 1 35 1 35 1 36 1 37 1 37 1 37 1 38 1 39. Nu cLeu� amti g u u�. 1 39. Long s pina l t r a c t s. 1 40. '. l.

(11) X. TABL E OF CONTENTS CONTINUED : PAGE PART V :. THE PATHOLOGY OF STRINGHALT. 1 42. I n t roduct i on. 1 42. Ma t e r i a l s a nd Met hods. 1 43. Endos cop i c examina t i on. 1 43. Pathology. 1 43. Re s u l t s. 1 44. Endoscop i c f i ndings. 1 44. Mu s c l e p a t h o l ogy. 1 44. Pathology of per i phera l nerves. 1 47. L i ght m i croscopy. 1 47. Tea s e d f i bre prepara t i on s. 1 48. E l ec tron m i cr o s copy. 1 50. Morphome t r y. 1 51. F i bre d i ameter d i s t r ibut io n s. 1 51. I n t e rnode l engths. 1 52. Centra l nervous s y s tem patho l og y. 1 54. Di s c u s s ion PART VI :. 1 53 .. F I NAL DISCUSSION. 1 59. REFERENCES. 1 71. APPENDICES. . 27 6. Appendi x 1. Compo s i t i on o f t h e So l u t i on s U s ed f or Proc e s s ing Nerve Samp l e s. 276. Append i x 2. Embedd i ng Re s i n. 278. Append ix 3. Sta i n i ng Method for E l ect ron M i cros copy. 279. Append i x 4. S t a i n i ng Met hod s for Mu s c l e T i s s ue. 280. Append i x 5. Proce s s ing a nd S t a i n i ng Method s for Central Nervou s S y s t e m T i s sue. Append i x 6. 282. L i ght M i c ro s cop i c Morphol ogy o f Equine Per i pher a l Nerve. 285.

(12) xi. TABLE OF CONTENTS CONT INUED : PAGE Append i x 7. L ight M i c ro s co p i c Morphometry o f Equ in e Recurrent Larynge a l nerve. Append i x 8. Grading of Tea sed Mye l i na ted F i br e s From Equ i ne P e r i phe ra l Nerve. Appendi x 9. 302. E l ec t ron M i c ro s co p i c Morphology o f Equ ine P e r i phera l Nerve. Appen d i x 1 1. 298. I n ternode Lengt h s i n Equ i ne Recurrent L a ryngea l N erve s. Append i x 1 0. 2 97. 308. L i ght M i cros copi c Morphometry a nd I nternode Length s i n Recurrent Laryngea l Nerve i n S t r i n gha l t. 31 6.

(13) xii. LIST OF TABLES. PAGE. TABLE. 70. 1. Expe r i menta l anima l s. 2. Mye l i nated f ibre l o s s i n equ ine recurrent 81. l a ryngea l nerve 3. The frequency of i nd iv idua l nerve f ibre changes i n equ ine recurrent l aryngea l 82. a nd l imb nerves 4. 2 D en s i ty of mye l i na t ed f i bres (no . / mm ) i n 84. equ i ne recurrent l arynge a l nerve 5. Mean mye l i nated f i bre d i ameter (�m ). in 86. e q u i ne recurrent l aryngeal nerve 6. Mean mye l i na ted f i bre d i ameter (� m ). in. i n tra l aryngea l bran c h e s of t h e equ ine r e c urrent la ryngea l nerve 7. P e r c entage of abnorm a l t e a s ed mye l inated · f i bre s i n equ i ne recurrent l aryngea l n e r v e s. 8. 88. Grade s (a f te r Dyck ,. 89. 1 9 7 5a ) o f abnorma l. f i br e s i n equ i ne recurrent l a ryngea l a nd l imb nerve s 9. Mean internode length and var i a t ion i n equ i n e recu rrent la ryngea l nerve. 1 0. 91. Mu s c l e patho logy in control hor s e s. 93 1 22. Cont ' d.

(14) xii i. LIST OF TABLES CONTINUED TABLE 11. PAGE M u s c l e patho logy i n subc l in i c a l laryngea l 1 23. hemi p l eg i c horse s 12. Mu s c l e patho l ogy i n c l i n i c a l l a ryngea l 1 24. hem i p l e g i c hor s e s 13. The frequency of axona l s pheroids i n the. 1 38. l a t e ra l cuneate nu c l e u s 14. W e i g h t s of the l ar ynge a l mu s c l e s (g ). in. s t r i ngha l t. 1 45. 15. Mu s c l e pa thology i n a c a s e o f s t r i ngh a l t. 1 46. 16. Grad i ng of teased f ibres of recurrent l a ryngea l and l imb nerves f r om a hor s e w i th 1 49. s t r i ngha l t 17. . Mean mye l i na ted f i bre d iame t e r s (�m ). i n the. r ecurrent laryngea l nerve s f rom a hor s e 1 51. w i th s t r ingh a l t 18. Mean i n t ernode length of norma l ( A ) f ibres o f recur rent larynge a l nerve f rom a h o r s e 1 53. w i th s t r ingh a l t 19. D i f ferences in the d i s tr ibu t i on s of mye l inated f i bre d i ameters be twe e n contro l (1 ) , s u bc l i n i c a l (2 ) and c l i n i c a l (3 ) l a rynge a l 2 97. hemi p l e g i c anima l s 20. Grad ing (a fter Dy ck , 1 9 7 5 a ) o f tea sed mye l i na t ed f ibre s in the recurrent l aryngea l 298. n e rves o f control hor s e s Cont'd�.

(15) xiv. LIST OF TABLES CONTINUED PAGE. TABLE 21. Grading (af ter Dyck , 1 9 7 5a ) o f teased mye l i na t ed f ibre s i n recurrent l aryngea l ne rve s o f subc l i n i c a l laryng e a l hem i p l e g i c a n i ma l s. 22. 299. G r a d i ng (af ter Dyck , 1 9 7 5a ) of teased mye l i n a ted f ibre s i n recurrent laryngea l nerves o f c l i n i ca l l a r ynge a l hem ip l eg i c 300. a n i ma l s 23. G r a d i ng (af ter Dyck , 1 9 7 5 a ) qf tea sed m y e l i n a t ed f ibre s i n l imb nerve s from 301. c l i n i c a l la rynge a l hem i p le g i c hor s e s 24. I n ternode length s t a t i s t i c s of norma l (A ) f i br e s in equ i ne recurrent 302. l a ryngea l nerve 25. I nternode length s t a t i s t i c s of norma l (A ). inte rnodes i n equ i ne recurrent 303. l a ryng e a l nerve 26. I n te rnode length s ta t i s t i c s o f tota l f ib r e s 3 04. i n equ ine recurre n t l a ryngea l nerve 27. I n t e rnode length s t a t i s t i cs o f tota l i n ternod e s in equ i ne recurrent laryn gea l nerve. 28. D i f f erences in the d i s t r i but ions of. 305. i n t e rnode. l e ngth of type A f ibre.? between groups of contr o l ( 1 ) , subc l i ni ca l (2 ) and c l i n i c a l hem i p l e g i c hor s e s. (3 ) l aryngea l 306. on+-'. 0.

(16) XV. L I ST OF TABLES CONTINUED. PAGE. TABLE 29. Di f f erenc e s i n the d i s tr i but i on s o f inte rnode length o f tota l f i bres between groups of con t r o l ( 1 ) , subc l i n i c a l ( 2 ) and c l i n i c a l ( 3 ) l a rynge a l hemipleg i c 3 07. . anima l s 30. D i f f erences i n the d i s t r i but i on s o f mye l i nated f i br e d iame t e r s be tween s t r i ngha l t (1 ) a nd c l i n i c a l l arynge a l hem ip l eg i c (2 ) a n i ma l s. 31. 31 6. I nt e rnode length s tat i s t i c s o f recurrent laryngea l nerve s f rom a horse w i t h 317. s t r i ngha lt 32. D i f f erences i n the d i s t r i but i ons o f i n t ernode length o f norma l (A ) f ibres between g r oups of control (1 ) , l a ryngea l hem i p l eg i c ( 3 ) a nd s t r i ngha l t (4 ) h o r s e s. 33. 31 8. D i f f erences i n the d i str i but i on s o f i nternode l e ngth o f tota l f i bres between groups of contro l (1 ) ,. l aryngea l hem i p l eg i c ( 3 ) a nd. s t r i ngha lt (4 ) hor s e s. 31 9.

(17) xvi. LIST OF F IGURES. PAGE. F IGURE 1. A. l ine d rawing o f. the. paranod a l reg i on o f a i l lu s t ra t i ng. f ibre�. nerve. mye l i n ated. con s t r i c t ion o f the nod a l axon 2. 205. Drawi ng s of the s equence o f even t s i n A.. axona l. degene ra t i on. a nd. regene r a t i on ,. and B. 3. �egmenta l �emy e l i nation a nd remye l i na t i on. L i ne. drawi n g s. S c hwann. of. ce l l. the. f orma t i on. ne twork s ,. during. of. axon­. the. phago­. cyto s i s of axon a l debr i s 4. E l e c tron of. equ ine. mi c rogr aph recurrent. of. 2 07 a. transverse. s e c t ion. l a ryngea l nerve. show i ng 208. a c l u s ter of regenerat ing f ibres . x 37 0 0 5. E l e c tron of. equ ine. m i c rograph recurrent. a ma s t ce l l . 6. L i ne the. of. a. mye l i nated. anatomy. a. transver s e. l a rynge a l. nerve. sect ion s howing 208. x 13 6 0 0. d rawing. large. of. of. l ong i tud ina l. nerve. nod e s. f ibre ,. v i ew. of. a. i l lu s trat i n g. o f Ranv i e r and. inter­. nod a l segment s 7. L i ne a. drawing. 209 of. a. t r a n sverse. s ma l l mye l i na t ed nerve f i bre ,. the. 206. r e l a t i on s h i p. of. the. mye l in sheath w i t h the axon. s e c t ion. of. i l lu s tr a t i n g. S chwann. cell. and 2 10.

(18) xvi i. PAGE. FIGURE 8. E lec tron. m i crograph. l a ryngea l. nerve. w i th i n. the. of. showing. Schwann. a. E l ectron. m i cr ograph. l a ryngea l. nerve. X. 10. of. a. lame l l a ted. of. recurrent. a. band. recurrent of. a. tran s ver s e nerve. (+. body. a mye l inated. m i c rograph. of. recurrent (1 ). a. in. S c hwann. nerve. f ibre .. s e c t i on. l a ryngeal nerve. showing. in the Schwann c e l l cytop l a sm x 1 0500. E l ec tron. a. m i c rograph. equ ine. of. r e c u r rent. conv o l u t ed. 21 2. tran s verse. laryngea l. ba s ement. E l ec tron equine. m i c rogr aph r e current. of. a. E lectron of. equ ine. m i c rograph. laryngea l. r e current. a co l lagen pocket . 15. of. a. showing. membrane x. tran sverse. a n " on i on bu l b " f ormat i on. s e c t i on. nerve. i a ted with a S c hwann ce l l proce s s .. 14. showing. t r a n s verse. o f a mye l i n a ted f i bre .. of. s e c t i on. 21 2. equine. e x ce s s. 1 3. Bungner .. 1 3600. E l ectron. of. a 21 1. equine. l a ryngea l. mye l i n. cytop l a sm of. l i pi d drops. 12. of. x 48600. s howi ng. m ic rograph. equine. of. cytoplasm. 21 1. of. ce l l. 1 1. granu l e. 1 1 200. E lect ron. X. recurrent. protagon. cell. mye l i na t ed nerve f i bre . 9. equ i ne. nerve. a s so c -. 1 7500 s e c t i on showing. 21 4. x 6300_ transverse. la ryngea l. nerve. 21 3. s e c t ion showing. x 26200. 21 4. S i te s o f re current l a rynge a l and vaga l nerve samp l e s. 21 5.

(19) xviii. FIGURE 16. PAGE Course. of. the. r e current. l aryngea l. n e rve 21 6. immed i a t e l y c a ud a l to the l arynx 17. Anatom i c a l. relat ionships. of. the. recurrent. l a ryngea l and vaga l nerves in the midcervi c a l region. 21 7. 18. Te chnique o f we ighted nerve f i x a t ion. 21 8. 19. Technique. for. obt a i n i ng. s ingle. tea s ed nerve. f i bres. 21 9. 20. Tea s ed f i bre c l a s s i f i cat ion. 220. 21. A. photomi cr ograph. of. the. the. are a. control X. 22. r i gh t. of. a. recurrent. of. the. a n i ma l .. t r a n s verse larynge a l. thorac i c. s e c t i on nerve. i n l et ,. Pheny lened i am i ne. f rom. in a. s t a i n i ng . 221. 200. Photomicrographs of. the. left. a. c l in i c a l. sections. tran sver s e. of. recurrent. laryngea l. nerve. hor s e .. hem i p le g i c. l a ryngea l. f rom 222. Pheny lened i a m i ne s t a i n i ng . x 2 0 0 23. Photom i c rograph s of. the r ight. a. c l in i c a l. of. transver s e. recurrent. l aryng e a l. l a ryngea l. A. photom i crograph. of the. the. left. of. a. recurrent. midcerv i ca l. area. f rom. h or s e . 223. x 200 tran s ve r s e. s e c t ion. l aryngea l f r om. l aryngeal hem i p l eg i c hor s e . s ta i ni ng . x 4 0 0. nerve. hem i p l e g i c. Pheny l ened i amine s t a i n i ng . 24. s e c t ions. a. nerve. in. c l i n i ca l. Pheny lened i a m i ne 224.

(20) xix. F IGURE 25. PAGE A. photomi c r ograph. of. the. r i ght. immed i a t e l y. of. t r a n s verse. recurrent. caud a l. cl inical. a. to. l aryngea l. l ar yngea l. the. l a rynx. nerve f rom. h em i p l e g i c. ·. s e c t i on a. hor s e . 224. Pheny l ened i a m i ne s t a in i ng . x 4 0 0 26. A. photomi c r ograph. of. the. the. left. of. a. recurrent. m i dcervi c a l. t r a n s verse la ryngeal. area. f rom. larynge a l hemi p l e g i c hor s e . s t a i n i ng . 27. A. the. the. nerve. a. in. cl inical. Phe nylened i am i ne 225. x 400. photomi crograph. of. s e c t i on. left. of. a. recurrent. m i d ce rv i ca l. t r a n sverse l a rynge a l. area ,. f rom. l aryngea l hem i p l e g i c hor s e .. a. s e c t i on. nerve. in. subc l i n i c a l. Phe nylene d i am i ne 225. s t a i n i ng . x 4 0 0 28. Photom i c rograph. of. tran s v e r s e. sec t i on s. of. t h e branche s of t h e r i ght r e cu r r ent l a ryngea l nerve. 29. i nnervat ing. the. abductor. and a dductor. mu s c l e s. f rom a c l i n i ca l l arynge a l hem i p l e g i c. hor s e .. Pheny l ened i a m i ne s t a i n i ng . x 2 0 0. A of a. photom i crog raph the. of. a. left. super f i c i a l. c l in i c a l. la ryngea l. t r a n s verse. s e c t ion. pe rone a l nerve f rom h em i p l eg i c. hor s e . 227. Pheny l en ed i a m i ne s t a i n i ng . x 2 0 0 . ' , 30. A of. photomi crograph the. left. of. tibial. a. t r a n sverse. nerve. l aryngea l hem i p l eg i c hor s e . s t a i n i ng . x 2 0 0. 226. f rom. a. s e c t ion c l i n i ca l. Phenylened i am i ne 227.

(21) XX. FIGURE 31. PAGE A. pho tom i crograph. of. the branch o f. of. a. t r a n s verse. peronea l. nerve i nnerva t i ng. the � x t �n � o � digit o � um l o n gu � a. cl inical. laryngea l. A. pho tom i crograph. of. the. r ight. a. clinical. of. A. a. common. of. hor s e . 227. t r a n s verse. pe ronea l. l a ryngea l. photomi cr ograph. f rom. x 400 s e c t i on. nerve. hem i p le g i c. Pheny l ened i am i ne s t a i n i ng . 33. mu s c l e. h em i p l e g i c. Pheny l ened i am i ne s t a i n ing . 32. s e c t ion. f rom hor se .. x 200. a. 228 .. t r a n s verse. s e c t ion. o f the branch of the perone a l nerve i nnerva t ­ ing. the. f r om. a. �xt�n� o � digit o �u m l o ngu.!>. c l i n i ca l. l a ryngea l. h em i p l e g i c. Pheny l ened i a m i ne s t a i n ing . 34. A. photom i crog raph. of. the. the. r ight. of. mid c e rv i c a l. hor s e .. x 200. a. 228. t r a n s verse. recurrent. mu s c l e. l ar yngea l. a rea. of. l a ryngea l hemi p l e g i c hor s e .. a. s e c t i on nerve. in. subc l i n i c a l. Pheny lened iamine 229. s t a i n i ng . x 4 0 0 35. A of. photom i crograph the. left. of. a. t r a n s verse. recurrent. s e c t ion. l aryngea l. nerve. immed i a t e l y cauda l to the l ar yn x of a control hor s e . 36. A of. Pheny l end i am i ne s t a i n i ng .. photomi cr ograph the. r i ght. immed i a t e l y clinical. of. a. t r a n s verse. r e current. caud a l l a ryngea l. to. the. l a ryngea l l arynx. h em i p l e g i c. Pheny l ened i am i ne s t a i n ing .. x 400. 230. x 400 s e c t i on nerve f rom. a. hor se . 230.

(22) xxi. PAGE. F I GURE 37. A. phot omicrograph. of. the. right. immedia t e ly. of. a. t ransverse. recurrent. cauda l. to. s e ction. l aryngeal. the. l arynx. nerve f rom. a. 1 day o l d foa l showing Renau t bodies . Pheny l en ediamine staining . 38. A. photomicrograph. of. the. the. right. l ev e l. of. a. recurrent. of. the. laryngeal. A. photomicrog raph. of. the. the. right. a. of. recurrent. midc ervica l. a rea. Histogram. of. the. nerve. inlet. f rom. dis t ribu tion s. l a ryngea l. nerve. a. hor s e . 231. t r a n s verse l aryngea l a. s e c tion nerve. contro l. in. hor s e . 231. x 40. mye lina t ed. diam e t e r. at. 1 00. X. f rom. Phen y l endiamine s tainin g . 40. s e c tion. h emiplegic. Pheny l endiamine s t aining . 39. 231. transverse. thora ci c. l aryngea l. c linic a l. x 400. of. immedia t e l y. nerve. the. fibre. recurrent. caudal. to. the. larynx 41. His togram diamet e r. 232 of. the. myelin a t ed. dis t ribution s. of. nerve. the. fibre. recurrent 233. laryn geal nerve in the midc e r vical area 42. His togram. of. the. myelin a t ed. diam e t e r. dis tribution s. l aryngea l. nerve. in. the. of. nerve. the. a re a. of. fibre. recurrent the. aortic 234. arch 43. Histogram. of. the. myelinated. diame t e r. dis t ribution. of. nerve. fibre. int r a l a ryngeal. branc h e s o f the recurrent l a r yngea l nerves. 235.

(23) xxii ... PAGE. FIGURE · 44. Photornicrographs. of. consecutive. portion s. o f a tea s ed mye l i na t ed fibre from the tib i a l nerve. of. a. c l in i c a l. l a ryngea l. hor s e , showing type B change . 45. Photorni crograph s of. a. teased. of. hemip l e g i c. x 40. 2 3�. c on s ecut i ve. mye l i n a ted. f i bre. por t i on s. f rom the. left. recurrent laryngeal nerv� 6 f a clin i cal l�ryngea l hem i p l e g i c hor s e s how ing type C 46. Photomi c rograph s of. a. tea s ed. r e current to. the. 47. larynx. a. hor se. f ibre. showi ng. f rom the. type. left. l a ryngea l D. change . 238. 40. a. t e a sed. of. consecutive. mye linated. f ibre. por tion s. f r om the. l a rynge a l nerve i n the m i d c e rv i ca l. area. a. of. c l i n i ca l. l a ryngea l. r e cu rrent to. the. larynge a l l arynx ,. hem i p l e g i c X. .. f rom the r i ght. a. c l in i c a l. showing. type. l a ryngea l G. change . 240. a. teased. recurrent to. por tions. 40. Photomi crographs of. 239. x 40. nerve immed i a t e l y caud a l. of. hor s e. h em i p l e g i c. c on s ecut i ve. of. Photom i c rograph s. (. left. recurrent. o f a teased mye l inated f i bre. 49. por t i on s. subc l i n i c a l. hor s e showing type F chang e . 48. 237. nerve i mmed i a t e l y c auda l. of. Photomicrographs of. consecu t i ve. mye l i na ted. laryngea l. hemip l e g i c X. of. c hange . x. 4 0. the. of. cons ecutive. mye l i na te d. laryngea l. la rynx. t ype I chang e .. of x 40. fibre. port i on s. f rom t h e. left. nerve immed iate l y cauda l a. control. hor s e. s howing 241. }. .·.

(24) xxiii. FIGURE. PAGE A. 50. photomi crograph. the. r i ght. of. recurrent. a. tea sed. l aryngea l. f ibre. nerve. f rom. at. the. l e v e l of the thora c i c i n l e t of a subc l in i c a l l a r yng e a l. d e genera t i on . 51. a. teased. re current area. of. hor s e .. X. A. chron i c. a xona l 242. x 40. Pho t om i c rographs of. 52. show i n g. horse ,. of. con s ecut ive. mye l i na ted. f ibre. por t i on s. from the. left. l aryngea l nerve i n the midcerv i ca l a. subc l i n i c a l. showing. l aryngea l. recent. a xona l. hem i p l e g i c. degenera t i on. •. 40. 242. photomi c rograph. f i bre nerve. from in. the. the. of. a. left. tea sed. mye lina ted. recurrent. midcervi c a l. area. l arynge a l. of a c l i nica l. l aryng e a l hem i p l e g i c hor se , showing paranoda l 24 3. d emye l i nat ion . x 1 0 0 53. Pho t om i crog raphs. of. of. recurren t. the. left. immed i a t e l y cl inical. caud a l. l aryngea l. t e a s e d mye l inat ed f i bre s to. l aryngea l. the. nerve. l arynx of. a. hem i p l eg i c horse ,. s ub­. showing 24 3. th i ck e n i ng s of the mye lin shea th . x 4 0 54. E l ec tr on of. the. m i crographs re curr ent. of. trans vers e. l ary ngea l. s ecti o n s. nerves. f rom 24 4. l aryngea l hem i p l e g i c hor s e s . 55. E l ec tron of. mi crog raph s o f. recurrent. trans vers e. l arynge a l nerve. f rom. s e ct i o n s l aryng e a l 24 5. hem i p l e g i c horse s 56. E l e c tron. mi crograph OD.a. of. recurrent. r i ght. tran sverse. l a ryngea l. nerve. s e ction in. the. mid c ervi c a l area from a s ubc l in i ca l l aryngea l hemip l e g i c anima l .. x 1 5300. 24 6.

(25) xxiv. FIGURE 57. PAGE E l ectron of. m i c rograph. r i ght. recurrent. m i dcer v i c a l. area. E lec t r on of. f rom. X. 59. nerve. c l in i c a l. s e c t i on in. the. l ar yngeal 246. t ran sver s e. l ar yng e a l f rom. a re a. nerve. control. a. s e c t i on in. the. hor s e .. 1 5300. 246. E l ectron of. a. of a. recurrent. m i dcerv i c a l. transver s e. x 1 9 20 0. m i c rograph. r i ght. a. l a r yngea l. hem i p l e g i c ani ma l . 58. of. m i c rograph s. equ ine. ne rve. of. recurrent. f ibres. transverse. s e c t i on s. l aryng e a l nerve. d i s t ended. w i th. showing. a ccumu lated. organe l l e s . 60 ·. E lectron of. the. 247. m i c rograph r ight. of. tibial. a. transver s e. nerve. f rom. a. s e c t i on c l in i c a l 248. l a r yngea l hemi p l e g i c an ima l . x 6 3 0 0 61. E l e c t r on. m i c rograph. of. r i ght. a X. 62. the. c linical. of a. common. transver s e. peronea l. l ar yngea l. s e c t ion. ner v e. hem ip l e g i c. f rom. an i ma l .. 1 9 20 0. Mean. 248. regre s s ion. per ime t e r mye l in. ( log. l ine s to. lame l lae nerve. l ar ynx. contro l ,. in. e). ba s e of. l ar yngea l. for the. axis and. c y l inder numb e r. left. i mmed i a t e l y. r e c urrent. caud a l. s ubc l in i c a l. of. and. to. the. c l in i c a l. l a ryngeal hem i p l e g i c an ima l s 63. Mean. regre s s ion. per i me t e r. ( log. l ine s to. for. ba s e. e). 249 axis and. c y l inder number. of. mye l in l a me l l ae of the l e f t r ecurrent l ar yngea l nerve. in. the. midcervical. area. in. c on t ro l ,. s ubc l in i ca l and c l in i c a l laryngea l hemip leg i c ani m a l s. 25 0.

(26) XXV.. PAGE. F I GURE 64. Mea n. regre s sion. pe rimeter mye lin. ( lo g. lin e s to. lame l l a e. for. ba s e of. a xis. e). the. a nd. cylinder number. left. of. r e cu rrent. la ryngea l nerve in the region o f the aortic arch. in. contro l ,. subclinica l. a nd. c linica l. anima l s 65. 251. lines. regre s sion. Mea n. perimeter. ( log nerve. l arynx. contro l ,. in. the. of. la ryngea l. e). ba s e. to. lame l l ae. mye lin. for. axis. cylinder number. and right. immedia t e l y. recurrent. ca ud a l. subc linica l. of. a nd. to. the. c linica l 2 52. la ryngea l hemip l egic anima l s 66. Mean. pe rime ter mye lin. ( log. of. nerve. in. contro l ,. of. e). ba s e. to. lame l l a e. laryngea l. for. l ine s. regre s sion. cy linde r. axis and. number. recurrent. right. the the. midcervica l. area. c linica l. and. s ub c linica l. of. l aryngea l hemip l egic anima l s 67. Mean. perimeter. ( log. to. lame l l a e. mye l in. for. l ines. regre s sion. ba s e of. e). 253. axis and. cy linde r number. right. the. of. recurrent. l aryngea l nerv e a t the level of the thora cic inlet. in. contro l ,. s ubc linic a l. and. c linica l. l aryngea l hemip l egic anima l s 68. 254. Longitudina l and t r a n sverse view s , i l l u s tr a t ­ ing. the. p l exu s. f ormation. which. result s. in. a l te r a tion in the number and size of f a s cic l e s over a short l e n g t h of nerve. 255.

(27) xxvi. FIGURE. 69. PAGE A. photomi crograph. of. the. mu s c le. left of. a. of. a. t r a n s ver s e. s e c t i on. c�i c o a � y t � n o i d � u � i a t � � aii�. con tro l. hor s e .. Myo s i n. ATPa s e. s t a i n i ng . x 4 0. 70. A. photomi crograph. o f the l e ft mu s c l e ho r s e .. 71. A. of. a. l a rynge a l. hem i p l e g i c. of. a. t r a n s ver s e. c � i c o a�yt�n o id � u h iat�� a iih. hor s e .. Myo s i n ATP a s e s ta i n i ng . x 1 0 0. a. cl inical. photom i crograph. l a r yngea l. of. a. c�i c o a�yt�n o id�u�. mu s c l e. a. f rom. clinical. photom i crog raph. of. the r i ght. l a r yngea l. hemi p l e g i c. of. a. f rom. the. hor s e .. s ame. 25 7. t r a n s ve r s e. i a t ��aii�. c l in i c a l. My o s i n. s e c t i on. ATPa s e. l a ryng e a l s t a i n i ng .. 257. 40 photom i crog raph. mu s c l e. of. a. t r a n s ver s e. c �i c o a � y t� n o id � u �. f rom. hemi p l e g i c. A. s e c t i on. i a t � �aii�. c � i c o a� y t � n o id�uh. of the l e f t. X. 25 6. Myos i n ATP a s e s t a i n i ng . x 4 0. A. A. hem i p l e g i c. t r a n s ve r s e. o f the l e f t. X. 25 6 s e c t i on. of. A. s e c t ion. Myos i n ATPa s e s t a in i ng . x 1 0 0. hem i p l eg i c. 75. t r a n s ver s e. mu s c le. mu s c l e. 74. a. s ubc l i n i ca l. photomi crograph. hor s e .. 73. of. c�i c o a� y t � n o id � u � iat�� aiih. o f the l e f t. 72. 25 6. the. ho r s e .. s ame. d o �� aii�. c l inical. Myo s i n. s e c t i on. ATPa s e. l a ryng e a l s t a i n i ng .. 40 photomi crog raph. 257 of. a. t r a n s ve r s e. s e c t ion. o f the norma l � x t�n � o � digit o � um i o n g u hmuscle f rom a contr o l hor s e . X. 40. Myo s i n ATPa s e s t a i n i ng. 258.

(28) xxvii. PAGE. F I GURE 76. A. photomicrograph. of. the. f rom. a. hor s e . 77. of. transverse. s e c tion. e xten � o � digi t o � um i o n g u �. mu s cle. subclinical. the. f rom. laryngeal. hemiplegic. Myo sin ATPa s e staining . x 4 0. 258 sections. transve r s e. of. Photomicrographs of. a. mus cle s. e x t en � o � digito� um i o n g u �. clinic al. laryngeal. hemiplegic. hor s e s .. Myosin ATPa s e s taining . 78. Sites. of. tis s u e. 259. s ampling. in. the. medulla. oblongata 79. Anatomical. 260 r elation ships. of. the ,_nu c i e u �. bm!i g u u � i n the -kidaii��o !i o ng a t a. 80. A. photomicrograph f rom. a m !i g u u �. le sion. of. of. the. the. the. hor s e. right. cresyl vio l e t . 81. right n u cleu� with. vagal. outlet from the brain s tem .. 261. a. nerve. par a s itic at�. it s. Luxol f a s t blue / 262. x 1 00. A photomicrograph of the normal le f t n u c l e u � a m !i g u u � f rom a clinical laryngeal hemiplegic. a nimal . X. 82. A. Luxol. fast. 262. photomicrogr aph. laryngeal. of. hemiplegic. the. normal a bove. a nimal .. right. clinical. Luxol. fast 262. x 40 normal. le f t. f rom a control hor se .. Luxol. photomic rograph. n u cieu� am!i g u u �. the. f rom. blue / cre syl vio l e t . A. violet .. 40. n u c i e u� am!ig u u �. 83. blue/ cresyl. of. f a s t blue / cr e s yl viole t .. the x 40. 263.

(29) xxvi i i. F I GURE 84. PAGE A photomi crog raph of the norma l a. f r om. a m£..i g u u�. hem i pleg i c. hor s e .. lef t n u cl�u�. subc l i ni c a l fa s t. Luxol. l a ryngea l blue / cr e s y l. v i o l et . x 4 0 85. A. pho tomi crog raph. cuneate ho� s e ,. ( +) 86. 263. of. the. r i ght. l a te r a l. nuc l e u s from a subc l i ni ca l l a ryngea l s howing. numerou s. a xona l. spher o i d s 264. H + E . x 1 00. A photom i c rogr aph of the l e f t l a t era l cuneate nuc l eu s. f rom. a. subc l in i c a l. show i ng numerous axon a l X. l aryngea l. sph e ro i d s. hor s e ,. (+ ). H + E. 1 00. 264. 87. Sampl i ng l ev e l s of the peron e a l nerve. 88. A. photomi crog raph. of. the a. f rom. of. a. tran s ve r se. c�i c o a�yt�n o ideu� l at�� a li�. hor s e. a f f e cted. w i th. 265. s e c t i on mu s c l e. str i ngha l t . 266. Myos i n ATPa s e . x 4 0 89. A a. tran s v e r s e horse. of. s e c t ion. a f f e c ted. w i th. the. r i gh t. mu s c l e. f rom. s t r i ng ha l t .. Myo s i n 266. ATPa s e . x 4 0 90. A of. photom i c rog raph left. hor s e. of. a. t r a n s ve r se. t.i..R ia l i � c �a niali�. w i th. a f f e c ted. mu s c l e. s t r i ngha l t .. s e c t ion f rom. a. Myos i n 267. ATPa se . x 4 0 91. A. transve r s e. c a �pi �adiali�. s e c t i on mus c l e. w i th str i ngha l t .. of. the. f rom a. r i ght tl�x o � hor s e a f f e c ted. My os i n ATPa s e . x 40. 267.

(30) xxix. PAGE. FIGURE 92. A. photomi c r ograph. of. norm a l. in. the. left. a re a. of. of. a. t r a n s verse. recurrent the. s ec tion. laryngeal. aortic arch .. nerve. Pheny lene-. diamine s t aining . x 2 0 0 93. A. photomicrogra ph. of. the. left. immediat e l y hor s e. of. 268. a. t r a n s verse. recurrent. cauda l. a f f e c t ed. to. with. s ec tion. l a ryngea l. the. nerve. l a r ynx ,. s t ringha l t .. f rom. a. Pheny lene­. diamine s taining . x 2 0 0 94. A. photomic r ograph. of. the. the. left. area. of. of. 268. a. recurrent the. t r a n s verse l a ryng e a l. aortic. a rc h ,. a f f ected wit h stringha l t .. 95. A. the. s taining . 96. A. of. the. hor s e. s ection. t r a n s verse f rom. nerve. a. hor s e. Phenyl enediamine 269. right. a f f ected. a. 200. photomicrograph. of. f rom. in. Pheny l enediamine. s t ringha l t .. by X. a. tibia l. right. a f f ected. nerve. 268. photomi crograph. of. s ection. x 200. s taining .. by. of. a. median. t r a n s vers e. nerve. s t ringha l t .. s e ction. f rom. a. hor s e. Phenyl enediamine 269. s taining . x 2 0 0 97. A. photomicrogra ph. of. the. the. left. area. a f f ected. of by. of. a. recurrent the. t ra nsverse l a ryng e a l. aortic. s t ringha l t .. a rc h ,. s e c tion nerve. f rom. a. in. hor s e. Phenyl enediamine 269. s taining . x 4 0 0 98. A. photomi c r og raph. the. left. ha. t�. x. of. recurrent. midcervi c a l 100. ·. area,. a. t e a s ed. l a ryngea l. f rom a. fibre. n erve. hor s e with. in. f rom the. s t ring­ �70.

(31) XXX. FIGURE 99. PAGE A. photomicrog raph. of. a. tea s ed. fibre. f rom. the righ t ·deep peron e a l ner- ve f rom · ·a ho�se with x .1 0 0. s t ringha l t . 1 00. Photomic rographs of. a. t ea sed. recurrent. 270. of. consecutive. por tion s. myelinated fibre f rom the right .. l aryngea l. nerve. at. the. l evel. of. the thoracic in l e t f rom a hor s e with st ringx 40. ha l t . 1 01. Photomicrograph s of. a. X. of. c o n s e c u tive. t ea sed mye lina ted. median. 1 02. 271. nerve. of. a. fibre. hor s e. por tion s. from the right. wit h. stringha l t .. 40. E l ectron. 272. mic rograph s. of. t ra ns verse. s ec tion s. f rom the hind limb nerves of a hor se a f fec ted 273. with s t ringha l t . 1 03. E l ectron. micrograph s. of. t r a n s verse. s e c tion s. f rom the recurrent laryn g e a l and limb nerve s 274. o f a horse a f fec ted with s t ringha l t . 1 04. Histograms diamet e r. of. the. mye lina ted. dist ribu tion s. of. nerve. the. fibr e. recurrent. l a ryng ea l nerves f rom a hor s e with s t ringh a l t. 275.

(32) 1. PART I. INTRODUCTION. I NTRODUCTION R es p i ra tory d i s ea s es n es s. in. 1 9 65 ) .. th e. h or s e. On e. of. l a ryng ea l t o as. (Br i t i sh. th e. mo s t. h em i p l eg i a ,. roa r i ng .. v i rtua l ly to. ar e s econd. s ince. We i s s. Equ i n e Ve t erinary. cond i t i on. d i s ea s e h a s. th e i nc ept i on. ( 1 937 ) ,. of. 5%. c ond i t ion .. The. c l i n i ca l. h em ip l eg i c. h o r s es. r es u l t. all. of. Dur ing. ex erc i s e. d y s pnoea , a. and. r edu c t i o n. th i s. in. th e. of. or. and. important. by. and. l a ryng ea l of. th e. c a r t i l ag e.. s t r i dor. a i rwa y of. the. s ub s equent. i n s p i ratory. a b i l i ty. a ccording. d ev el op. th e a ryt enoi d. l a ryng ea l. r ef er r ed. pa r a l y s i s. mu s c l e,. in. is. t h e Thoroughbr ed. exh i b i ted. of. results. b ec au s e. often. th e breed ,. p a re s i s. l os s. mov ement. is. d i seases. Thorou ghbr ed s. c�i c o a� y tLn o i dLu4 d o �4ali4 of. A s s o c i a t i on ,. th es e. that. s igns f rom. of. b l i ghted. of. l ef t. control. importanc e on l y to l a m e­. i mpor t a nt. a. Th i s. in. a nd. o b s t r uc t i on ,. th e. animal. to. ·p erform a th l et i ca l l y . A l though. th e. c au s e. of. i n s om e f ew a n i ma l s d amag e. to. c h em i ca l. the. as. a l though. recurrent. f a c tor s. V et er i na r i a n s. hav e. d i s ea s e i s. para l y s i s. is. to trauma t i c or. l a ryng e a l. th er e i s. in. n erv e,. or. to. k nown. i r r i ta n t p l an t. or. no hi s t ory of a n y o f th es e. th e m a j o r i t y. trad i t i on a l l y. i d iopath i c thi s. l aryng ea l. to b e r el a t ed. i n t o x i ca t i on s ,. a et i o l og i c a l c a s es. th e. of. a f f ec t e d. r ef erred. l aryng ea l. to. h em i p l eg i a. a n i ma l s .. t h es e ( Cook ,. s t r i c t l y cor r ect .. An. l a t t er. 1 976 ) ,. t erm. is. not. i d i op a t h i c. d ef i ned. in. th e Conc i s e Oxford D i c t i ona ry. ( 1 964 ). a s a d i s ea s e w h i c h i s not preceded or occa s i o n ed by anot h er . B l ack 1 s s ta t es. M ed i c a l tha t. D i ct iona ry. i d i op a t h i c. is. ( 1 965 ) a. tak es. t erm. i nd i c a t i n g that th ei r cause i s unknown . is. d e f i ned. by. B la c k 1 s. Med i c a l. a. w i der. appl ied. to. v i ew ,. and. d i s ea s es. Th e word h em i p l eg i a. D i c t i onary. as. a. p a ra l y s i s.

(33) .2. a f f ec t i ng. on e. u s u a l ly. r ef er s. f er en c e. with. wh en. th e. i n oth er s it. a. th es i s ,. t h en the. in. f unct ion. t erm. in. f or th e. is. is. to. to. is. n ec es s a r y. to. in. which. c a u sa l. d i s t i ngu i s h. is. s om e. Lar y ng ea l i m p r ec i s e,. the. u nd er l y i ng t h e l a rynx , In. h em i p l eg i a only. l a ryng ea l. known ,. a nd. wh i l e. is. h em i p l eg i a. b etw een. In. s p ec i f i ed .. l a ryn g ea l. l a ryng ea l. f a c tor. that. not. u s ed. h em i p l eg i a ,. on e s i d e o f. is. i n t er ­. is. part i a l .. cond i t ion. impr es s ion. l i m i t ed. du e to. par es i s. on l y is. Pa ra l y s i s. a h em i par es i s .. thi s. i d iopa t h i c. p r ef er enc e. wh er ea s. hor s es. it. sy s t em .. funct ion ,. is. th e s i d e invo l v ed. t erm. the. motor. s y s t em ,. s een. c onv ey s. s p ec i f i ed. of. s p eaking. d y s f un c t ion. ev en. u s ed. los s. motor. s t r i c t ly as. th e. n ervous. of. wron g l y. n ervou s. of. cond i t i o n. h em i p l egi a ,. and. the. the l o s s. c a s es ,. as. s id e ' to a. th i s. wi l l. be. w h en. it. h em i p l eg i a. oth er. c a s es. of. th e d i s ea s e. Cl inical. s igns. of. i n you ng adu l t s. et al..,. Marks. of. which. i nvo l v ed. b ecom i ng. (G o u ld en. &. d i s ea s e i s and. is. a. in. 1 9 02 ;. M a s on , of. in th e. roa r er. wa s. its. a. it. popu l a t ion. a lwa y s. w i th. atrophy. a s s o c i a t ed m u s c l es ,. s econdary. r ec u rr ent. l a ry ng ea l. n erv e (Hoa r e,. M a r k s e t af. ,. to. 1 970a ;. at. occurs of a. a. 2 on. th e. M a s on ,. s t udy. in. c ompa r i son. f rom. w hi ch. y ea r s a s p ec t. th e age th i s. t h e l ef t. s i d e,. l ef t. Co l e,. 1 973 ;. of of. n europa thy. 1 91 5 ;. 1 970 ;. th e r el a t i v e r i s k. i n t er es t ing. a l mo s t. Cook ,. r ec ent. analy s i s. g r eat es t. l a ryng ea l 1 970 ;. In. 1 91 5 ;. t h e s t udy w er e· tak en ,. An eerson , . 1 .9 8 1 ) . A n that. Hoa r e,. 1 97 3 ) .. i nc lu d ed. th e ag e d i s tr ibut ion. h o r s es. h em i p l eg i a a r e us ua l ly ma n i f es t. (Wi l l i ams ,. 1 9 7 0b ;. Thoroughbr ed s , of. l a ryng ea l. i nt r in s i c. of. th e. 1 946 ;. l ef t Cook ,. Duncan e t a f. ,. 1 97 4 ) . Th e. purpos e. n a t ur e. and. l a ryng ea l as. a ba s i s. of. th i s. d i s t r i b u t i on. n erv es o f to. th e. is. of. to. a c cura t el y. pathology. i d iopa t h i c. in. the. d ef i n e. th e. r ecurr en t. l a ryng ea l h em ip l eg i c hor s es ,. a l l ow i ng a b et t er und er �tand i ng of th e patho­. g enes i s of th e d i s ea s e. on. t h es i s. a n a t omy ,. A synop s i s of th e pr es ent know l edg e. p a t ho l ogy. a nd. s ugg es t ed. pr es ent ed and c r i t i c a l l y d i s cu s s ed .. a et i o l o g i es. is.

(34) (. 3. ANATOMY Th e. l ef t. t h ei r f rom. a nd. r i ght. a n a t om i c a l th e. a round. vagus. n euron es in. the. Both. the. l a rynx .. d i stal. to. c a v i ty. ( Co l e,. 1 946 ) .. a pprox ima t el y hor s e,. w i th. the. bra nch i ng. n erv es. f rom. of. than. 1 9 7 3) .. the. t o t h e l a rynx. t h ey. m ea s ur e u p. to. a ny. in. its. to. motor. motor. 1 00. cm ,. thora c i c i n c l ud ed ,. a nd. r i gh t. of. i n n erva t e. is. cm ,. oth er. of. are. th e. cours e 250. p a s s es. as. s uch. n er v e. in. count erpa rt. B eca u s e o f th e d i f f er ent l ev el s. l ef t. ( Co l e,. mus c l es. b e up. and. c en t r a l. t h e vagu s. ex c ept i on. th e vagus ,. than th e r i ght. the. in. branch es. n erv es. the. t h e v a ga l. l ong er. ( Duncan & G r i f f i th s , of. Wh en. l ength may. 1 00%. f rom. f rom. d i f f er. n erv e. th e n eck. n erv e can. s eparat i on. l eft. laryng ea l. cou r s i ng to. n erv es. th e r i ght ,. a s c end s. m i dbra i n. a xona l. t han. r ecurr en t. Th e l ef t. its. th e tota l th e. b ef o r e i t. l ength ,. in. Th e. mor e d i s ta l l y. 1 975 ) .. cons i d era b l e. l a ryng ea l. a rrang em en t .. t h e ao r t a. ( G etty ,. r ecurr en t. and. r i ght. th e l ef t. r ecurr en t. can b e up to. 31. l a ryng ea l c m long er. 1 946 ) .. PATHOLOGY Th e th e. und er l y i ng. i n n erva t i n g. n erv es. h em i p l eg i a ,. i nv o l v em ent. has. b een. B ou l ey. c entury . roar er ,. of. n erv e by i n l et .. In. roa r i ng. s ou nd. l a ryng ea l. the. ( 1 825 ) l ymph. mu s c l es ,. a. s i nc e. r eport ed of. th e. nod es. y ear ,. ho r s e,. by. l a ryng ea l. mu s c l es ,. appr ec i a t ed. same. in. the. t h es e. compr es s ion. en l a rg ed. of. l ef t. in. a nd. d iv i s i on. r ecurr en t. ( 1 825) ,. wa s t ing or. in. of. and. l a ryng ea l th e. ob s erv a t i on. th e a r ea. Dupuy. in. ea r l y. the. mu s c l es. 1 9th in. a. l a ryng ea l. o f t h e thora c i c r eprodu c ed th e. compr es s ion o f. the. a s soc i a t ed th e vaga l. or r ecurr en t l a ryng ea l n erv es .. D eta i l ed p o � t m o �t e m i n s p ec t ­. i on. of. of. th e. h em i pl eg i a th e. l ef t. l a ryng ea l wa s. mu s c l es. p er form ed. by. h a lf. its. u sua l. hor s e. P er c i va l l. c �i c o a�y t e n o ideu� d o � � a l i �. approx ima t el y. a. s i z e.. to. with. ( 1 840 ) , be. Th e. v ery. l a ryng ea l who. f ound. pal e. and. c�i c o a � y ten o i d e u �.

(35) 4. t h e vent�i c u La�i � ,. Late�aLi�,. e u� t�a n � ve�� u� m u s c l es c o l ou r l es s th e. a nd. mu s c l es. w er e. s carc ely. of. th e. th e vo c aLi� and t h e a�yte n o id­ r eport ed. r ec og n i s ab l e. r i gh t. s id e. w er e. to. be. as. " a l tog eth er. mu s c l es " ,. " u nusua l l y. wh i l e. r ed. and. s tron g " . Th e. p a t ho l o g i c a l. l a ryng ea l. n erv es. i n v es t i ga t ed. l i m i t ed. l a ryng ea l. of. cm. n erv e the. in. f rom. n erv e,. l es s. n erv e. Th i s. a dvanc ed. l ef t. r ecurr ent. h em i p l eg i a. not ed. a. w er e. distally. f ibr es ,. A l though. w i th. th e. th e l es ions w er e. ex tr em i t y. of. th e. l ef t. ch a n g es w er e found a t a d i s ta n c e. t h e l arynx .. In. Cad ea c. ·. who. th e d i stal. th e f a s c i c l es. f i br es .. of. the. l a ryng ea l. c el l s .. to. (vide int�a ) ,. f i nd i ng s. w ith. in. ( 1 897 ) ,. S c hwann. r ecurr en t. mark ed. hors es. Cad eac. of. be. 30-40. pr es ent. d eg en era t i on. pro l i f er a t i on to. of. by. d i s t r i but ed f ound. chang es. con tra st. f ound. to. mor e r ec ent. th e cha ng es. to b e mos t. compo s ed o f ma i n l y sma l l my el i na t ed. wa s. p erhaps. t echn i q u es. m er el y. a. r ef l ec t i o n. a va i l abl e a t. thi s. t im e,. of f or. th e s tudy o f n ervou s t i s s u e. In. Argy l e. 1 933 ,. c erv i ca l. l ef t. f ound. a. 5. r ecurr ent. h emi p l eg i a ,. an. work er s .. A t rophy. the. not ed .. An. a t t empt. n erv e. f i br es. of. the. that. th e. l ef t. l oc a t e. r ec u r r en t a l so. nuc l eu s. of. not. in. c entral by. t h e v ag a l. of. s i d e.. c el l It. ex ami n ed of. is wa s. th e motor. bod i es. of. u nc l ear. thi s. wh eth er. a ctua l l y f i b r es. nuc l eu s. the. of. th e d or s a l vaga l nuc l eu s .. the. th e. the. n erv es ,. in. th e. n erv e. ( 1 93 4 ) . wa s. He. ex ami n ed. and d eg en er a t ­. obs erv ed ,. on. th e l ef t. i d ent i f i ed. n u cf..e u � amRi guu� , r ecurr ent. a l so. of. Argy l e. nu c l eus. wa s. nu c l eu s. i n hor s es a f f ec t ed wi th l a ry n g ea l h em i p l egia , ion. hors e w i th. mu s c l es. l a ryng ea l. mad e. a. mid ­. v er i f i ed by o t h er. l a ryng ea l the. s egm ent . o f. n erv e,. o b s ervation. wa s. meduLLa o �L o n ga t a, s t a t ed. to. con s t r i c t ed. l a ryng ea l. l a ryng ea l. of. cm. th e. l aryng ea l. and. nu c l eu s. n er v e ,. or.

(36) 5. Th e f i r s t. d et a i l ed. h em i p l eg i a s ev er a l. wa s. und ertak en. r es ea r ch er s. m i c ro s cop i c f rom. patho log i ca l. Gr i f f i th s ,. 1 97 3 ;. Duncan �t a l ,. istic. of. th e. ion i n f i br e s i z e , f i b r es ,. the. f a s c i cu l a r wi t h i n. l i ght. and. el ec t ron. 1 972 ;. Duncan. 1 974 ;. �t a l ,. n erv e &. Duncan ,. Pa tho l o g i c a l f ea tu r es cha r a c t er ­ w er e. by. f ound. th e. i nc l ud ed. l ef t. in. t ho s e mu s c l es. r ecur r ent. l a ryng ea l. f ib r e typ e group i ng , v a r i a t ­. th e pr es enc e of a t roph i c and hyp er t r oph i c. d emon st rat ion. a t rophy ,. a nd. l a r y ng ea l. Mo r e r ec ent l y ,. (Gunn ,. Duncan. a t rophy. Th es e chang es. of. a f f ec t ed mu s c l e a nd. hor s es. 1 97 3 ;. i n n ervat ed. (1 9 4 6 ) .. mod ern. s t udy. 1 978 ) .. n eu r og en i c. l arynx. n er v e.. to. Gunn ,. Col e. u s ed. h em i p l eg i c. 1 975 ; of. hav e. t ec hn i q u es. l aryng ea l. by. i nv es t i ga t i on. b et w een. of. i ncr ea s ed. c en t ra l l y fat. f a s c i c l es ,. a nd. a nd. a. p l a c ed. nuc l ei ,. con n ec t i v e. t issue. loss. of. my el i na t ed. c l i n i ca l. or. end o s c o p i c. n erv e f i br es i n i n t ramu s c u l a r n erv es . A. large. numb er. ev i d en c e a t rophy. of of. r ec u r r ent. l a ryn g ea l c a s es 1 973 ;. wa s. but. s igns. of. of. hor s es ,. to wa s. Col e l es s. than. i n n ervat ed. hav e. b een. 1 946 ;. Duncan ,. 1 975 ) .. A t r ophy. in. of. no. Gunn ,. 27%. 26% of. (Duncan. &. c l inical. 5 0 % a trophy of. a. to. 1 972 ; of. the. l ef t. to. as &. Du n c a n. th e l aryng ea l exami n ed. by. show ed c l i n i c a l. mor e. r ec en t. s u r v ey. hav e th es e so. c a l l ed. Grif fiths , s igns. by. l a ryng es. In. w er e found. n eurog en i c. r ef err ed. th es e an ima l s. h em i p l eg i a .. (3 2% ) ,. l es i on s. (1 9 4 6 ) ,. and. shown. (Co l e ,. l a ryng ea l. subc l i n i c a l. have. mu s c l es. n erv es ,. only. 1 4. no. h em i p l eg i a. d emon s t ra t ed. (1 9 4 6 ) ,. 44. w i th. tho s e l a ryng ea l. G r i f f i th s , Col e. hor s es. l a ryn g ea l. subc l i n i c a l mu s c l es. of. 1 973 ) .. A c c o r d ing. w er e ob s erv ed. if. t h er e. th e c � i c o a�y t�n o id � u � d o� � a li �. mus c l e. I t app ea �ed. tha t th e· adductor mus c l e,. l at�� a li�,. wa s mor e. s ev er el y. a f f ec t ed. t h e c � i c o a � y t�n o id � u � d o � � ali� , c l i n i ca l ca s es & Gr i f f i th s , 1 975 ) . of. In. of. 1 97 3 ;. som e o f. n eu rog en i c. l aryng ea l Gunn ,. 1 973 ;. n. in. than. both. h em ip l eg i a. t hes e c a s es. a t rophy. th e c �i c o a�yt�n o id�u� the. c l inical. (Gunn ,. D u n c a n � t al ,. abduc tor , and. 1 972 ;. s ub ­. Dun c a n. 1 9 7 4 ; Dunc a n ,. th er e w as a l so ea r l y ev i d enc e. thos e. mu s c l es. suppl i ed. by. t he.

(37) 6. r ight. r ec ur r ent. l aryng ea l. f i b r e t y p e grouping f i b r es Gunn , In. (Co l e, 1 973 ;. a dd i t ion. ex a mi n ed n um b er. Gunn ,. Duncan ,. 1 975 ) .. to. s tudy i ng. took. 1 972 ;. and. vaga l. d eg en era t i on. of. not ed ,. r ec u r r ent in. par t i cu l a r l y l a ryng ea l. s ev er i ty. in. in a prox ima l. Th e. n er v es n er v e. part. r i ght. numb er. r ecu rr ent. of. n er v e f i br es. w er e a l so. l ary ng ea l n erv e.. f ou nd d eg en era t i on mor e o f t en. a. f i br es ,. of. th e. l ef t. d ec r ea s ed. and on l y ra r el y. a n y chang es i n th e r eg i on of th e aort i c arch . s ma l l. at. w i th on ly a f ew f i br es. a f f ec t ed a t th e l ev el o f th e thorac i c i n l et , a. C o l e (1 9 4 6 ). d eg en era t ion. d i r ect ion ,. 1 97 3 ;. endon eura l f ibro s i s. the distal. n erv e.. of. angu l a r. Dun c a n & Gr i f f i th s ,. l a ry ng ea l. Mark ed. f orm. atrophi ed ,. w i th pro l i f erat i on o f S c hwa nn c el l s and w er e. the. t h e l a ryng ea l mu s c l es ,. r ecur r en t. l ev el s .. Th i s. t h e pr es en c e o f. 1 9 46 ;. the. of. a nd. n er v e .. Col e ,. I n two c a s es ,. a f f ec t ed. in. th e. l i k e Argy l e (1 9 3 3 ) ,. i n tho s e f a s c i c l es con s i s t i ng. o f sma l l my el i nat ed f i br es . Emp l o y i ng. mor e. p er iph era l a nd. n erve,. pla s t i c. s co py ,. a. a nd. s hown. to. s ingl e. s ec t ions amount. cons i s t. a. of. p r epa r a t i on s. of. i n forma t i on. equ i n e. G l a s gow. obta i n ed. pr es en t. in. th e. h em i p l eg i a. (Duncan. Gr i f f i th s ,. r ecurr ent. variabl e. wa s. l a ryng ea l. Dun ca n ,. equ i n e of. s t udy. l i gh t and el ec tron m i c ro ­. 1 97 4 ;. Norm a l. •. f ib r e. th e. for. in. in. a t a l.. ,. n erv e. f or. a l t erat i o n s. n er v es. cowork er s. Du ncan 1 978 ). t echni qu es. pa t h o l og i c a l. l aryng ea l. Duncan. e. t al.. wa s. emb edd ed the. r ec u rr ent '1 9 7 3 i. nam el y. s ub s t an t i a l. r eg a r d i n g by. soph i s t i cat ed. &. 1 97 5 ;. Du n c a n. lary ng ea l. numb er. of. n erv e. f a s c i c l es. con t a i n i ng m edium s i z ed my el i na t ed f i br es , w i th a n occa s i on ­ al. s ma l l er. d i am et er. f ibre. p r es ent .. In. man ,. it. ha s. b een. d emon s t ra t ed t ha t . con s - id erabl e pl exus f o nna t ion of the fascicles occurs. a l ong. (S u th er l a nd. th e l ength. &. Swa n ey ,. of. 1 952 ) .. p erox i da s e t ra c er. t ec hn t�u es. th e. to. n er v e. l a rynx. are. f i b r es. d i f f u s el y. the. th e r ecurr ent U s ing. a r rang ed. in. n erv es. r etrograd e hor s er ad i s h. in the cat ,. a dductors. l a ryng ea l. a nd thi s. i t wa s. s hown. a bdu c t o r s n erv e. of. tha t th e. (Ma lmgr en '.

(38) 7. 1 977 ) .. i!.l al.,. f ib re s ,. Col le c t i on s. o f ten. present. of. in. sma l l. s eparat e. d i am e t e r. mye l i na ted. fascicles ,. were. s hown. to be s e n s ory f ibre s to the oesophagus and t r a chea (Duncan , 1 97 5 ) . and. The pre sence of unmye l i nated f i bres wa s demon s tr a t ed ,. c on f i rmed. with. ( vidi!. in/-11.a ). laryng e a l an ima l s. were. e l e c t ron a. m i c ro s c opy .. c ommon. nerve ,. but. were. a f fec ted. w i th. f i nd ing. of. and. the. l a rge. g i ra f fe. fast. recur r e n t. l a ryngea l. pos t u l a ted. that. left. nerve ,. the A. left. of. of. wh i c h. the. n e rve. l arynges. were. nine. we re. and. 40. f rom. a. the. to. be. were. f rom. l!.i � (1 97 8 ) .. c l i n i ca l. i n Thoroughbred s , 16. h a nd s. we re. r i gh t .. left. It. f i br e s. wa s. in. the. f a s ter on. grea ter length . Duncan. cases. of. f rom. number. ( 1 97 5 ) ,. l aryngea l. subc l i n i ca l. cases .. S i x o f the ca s e s ,. typ i c a l of the d i se a s e spectrum , w e r e d i s c u s s ed. in the report by Duncan three. in. numbe r. the. by. The 3 9 n o rma l a n i ma l s were ma inly pon ie s . said. in. to t rave l. exami ned. were. a. greater. conduc t i n g. c l i n i ca l. (4 5 . 5 % ). In. found. impu l s e s. were. recurrent. (Da l qv i s t i!.l a l. , 1 9 8 2 ) ,. in. fast. bod i e s. f requent l y. a nd thu s compens a t e for its. 88. hem i p l e g i a. than. l a rge. more. 1 981 ) ,. f i bres. nerve. the s e. a l low. s i de ,. tota l. (Harr i s on ,. condu c t i ng. norma l. hem ip l e g i a .. of other spec i e s , i n c l u d i n g the rat · man. in. observed. l a ryngeal. Renaut. (1 6 0. aged 5 ,. cm ). s ub c l i n i c a l. in. and. cases. Of the s e s i x a n i ma l s ,. of. l aryngea l. hemipl e g i a. 6 a n d 1 3 y e a r s a nd a l l we re ove r. h e i gh t . were. a l so. The. r ema i n i ng. three. Thoroughbr ed s .. ca s e s. They. were. aged 5 - 6 yea r s of age and each wa s over 1 5 . 2 hand s ( 1 5 5 5cm ) .•. in. h e i gh t .. The. at. a. of. number. arch . samp l e s. recurrent s i te s. laryngea l. be tween. the. nerv e s. l a rynx. were. a nd. s ampled. the. aor t i c. The vag a l ne rve s we r e a l s o co l l ec ted , a s we re d i s t a l of. other. pe r i ph e r a l. nerve s ,. i n c l ud i ng. the. u lnar ,. t i b i a l , d ig i ta l and phren i c . L i g h t m i c ros copy of the recurrent l a ryngea l nerves revea l ed pa tho log i ca l and. at. t he. cha nge. wa s. f ibre s. in. a l te r a t i o n s d i s ta l a. l ev e l. progre s s ive. the. left. at of. all the. d i stal. recurrent. leve l s. of. r i gh t . loss. of. l a ryngea l. the The. l e f t nerve , mo s t. l a rg e. obv i o u s. mye l i na ted. n e rve ,. w i th. no.

(39) 8. obs erva b l e decre a s e i n f i br e s i n the r ight nerve .. Clusters. o f regenera t i ng f i br e s and " on i on bu l b s " were s e e n frequent ­ ly. at. and. all. in. a t i on. l eve l s. of. the d i s t a l was. only. the. left. recurrent. r i ght nerve ,. r a re l y. wh i l e. obse rved .. l aryngea l. nerve. evidence o f degen e r ­. No. abnorma l i t i e s. we r e. detected i n a n y o f the other pe r iphera l nerves exami ned . U l t r a s tructura l ly , the. pre s ence. a xona l. organel l e s , on. the. i nc lud i ng. c on f i rmed ,. As. r emna n t s. obs erved. degene ra t i on. a ccumu l a t ion. mitochond r i a ,. the. wa s of. dense. and. by. not. a. in. a xon s. po s s e s s i ng. spl i t. of. l i gh t common. va r i ou s. a xona l. bod i e s ,. tubu l e-. a nd d i sorienta ted neuro f i l amen t s Wa$. s t ru c ture s , occ a s ions. we re. b a nd s ,. noted .. axona l. Howeve r ,. change s. Bungner. were. active. f i nding .. above. n umerous. degenerat i o n. m i c roscopy ,. l ik e. of. the. mye l in. seen. sheaths ,. i n ma s s i ve l y swol l e n axons and i n demye l i nated axon s . S i ng l e of the to. f i bre. chron i c form the. prepa r a t i on s demye l i na t i on. of. var i a t i on. presence. of. d emon s trated and. in. changes. remye l i nat ion .. i nternode. The se. l eng th ,. due. took. l ar g e l y. s egmen t s .. Howeve r ,. there wa s l i t t l e ev i dence o f a c t i ve demye l i na t i on .. A l t hough. a xona l. degene ra t i on. f ibres. were. paranoda l. s een. s h o r t i nterca l a ted. i nd i c a t i v e. wa s. to. obs e rved. show d i s t a l. demye l i n a t i o n .. hemipleg i a ,. d istal. In. t apering. of. only. occ a s iona l ly ,. s om e. degenera t i on a n d prox i ma l two. cases. of. con s e c u t ive. l a ry ng e a l. i nt e rnod e s. wa s. a f r equent f i nd i ng .. Few f i br e s w i th u n i formly short i n t e r ­. nod e s. S u ch. we re. s een .. regenerat i ng. f ibre s .. f i bres. the. f rom. c l i nical of. two. case , cont rol. Interca l a ted. t ib i a l and. changes. the. pon i e s. and. med ian. di stal revea led. s egment s f rom 1 0 0 t e a sed f i bres .. are. cha r a c t e r i s t i c. s e gment s. we r e. rare. p l antar. nerves. of. recurrent only. two. l a ryngea l. of in one. nerves. i nt erca l a ted.

(40) 9. F i bre. d i ameter. mye l i na ted to. f i bres ,. sma l l er. chang e s. h i s tograms and. d iameter. con f i rmed. i nd i ca t ed. f ibres. extended prox i m a l. in. the. a. marked. the. t o the. d i stal. of. of. a b s o l u te. s hi f t. nerve .. The s e. d i stal. l ev e l. loss. the a or t i c a r c h. i n one ca s e o f la ryng ea l hemipl e g i a . In. s ummary ,. mye l i na ted. there. f i bres. s e l e c t ively. wa s. in. a. the. left. af fecting. R egenerat ive. c lu s t e r s. all. l eve l s. of. the. d i stal. r ight. pa t ho l o g i c a l. the. subc l i n i c a l. a nd. In. d i a meter. were. l arynge a l. genera l ,. ob s e rved. hemipl e g i a ,. los s. l a ryngea l. bu l b s ". recurrent. were. l a ryngea l. larger. " on ion. nerve .. d istal. recurrent. the. left. chang e s. progr e s s i ve. in. f ibre s .. pre sent ,. of. both. bu t. nerve ,. nerve. all to · a. of. and. the. at in. above. c l i n i ca l l esser. a nd. degree. o f sever i ty i n the l a t t e r ca s e s . The. pred i l ec t i on. left. recurrent. Co l e. (1 9 4 6 ) ,. The. of. patholog i c a l. l aryng e a l. nerve wa s. Duncan e t a l. l a tt e r. (1 9 7 4 ). i nve s t i ga t ion. of. the s e. a l te ra t i on s. of. subc l i n i ca l. as. changes. a l so. in. we l l. the as. f or. t he. d i s ta l. noted by Cadeac. and. Dunca n. et al ( 1 97 8 ) .. demon s t rated recurrent. (1 8 97 ) ,. t he. pre sence. l aryngeal. c linical. cases. of. " on i on. bulbs ". nerve s. l aryngea l. hemipleg i a . Whi le. t he. recurrent. d emon s t r a t ion l a ryngea l. nerve h a s. years. (Duncan et a l. et al ,. 1 978 ) ,. in. earlier. f orma t i ons. for. that f i bre s. in. (Cadeac ,. the s e a nd. ,. remye l i na t i on. predom i na t e. Dunc a n ,. a. wa s. spec if i c i ty. proce s s noted . nerve. s i gns (Mad r id. 1 897 ;. " on i on bu l b s ". the. per iphera l w i th. a f f e cted. only been reported i n recent. 1 97 4 ;. s tud i e s. (1 9 7 8 ). in. 1 97 5 ;. Dun c a n. the �ro l i f erat i on of S chwann ce l l s wa s noted. s ig n i f i ca n c e o f e. t a l. of. of. of. Co l e , of. chron i c. l a rge. " on i on. demy e l i na t ion. Tea s ed. f ibre. s tu d i e s. wi th. " on i on. bu lb". 1 97 7 ) .. The. i s d i s c u s sed by Duncan. demy e l inat ion. et al ,. 1 946 ) .. Th i s. and. have. bu l b " and s hown. f orma t i on s , remy e l i na t ion. s i t ua t i on. e x i s te d. i n t h e recur rent la ryngea l n e r v e s from l aryngea l hem i p l e g i c a n i ma l s (Duncan e t al ,. 1 978 ) ..

(41) 10. Chang e s we re a l s o obs e rved i n the r i gh t recurrent laryng e a l nerve .. Howeve r ,. i nvo lvement. of. only. o f the r i ght nerve w a s demon s t rated , regene r a t i ng. clusters. and. the. d istal. por t i on. and even then a l t hough. " onion. b u lb s ". observed ,. were. there w a s no obv i ou s los s of mye l in a t ed f i bre s .. Th i s r i gh t. s ided nerve invo lvement substan t i a t e s the f i nd ing o f neuro­ genic. a trophy. in. t h e right s i ded l aryngeal mu s c l e s of. a f fec ted anima l s 1 97 5 ) As. both. left. d i sea s e in. 1 97 3 ;. Duncan. �t a£,. 1 97 4 ;. Dun c a n ,. •. i nd i cated. the. (Gu nn ,. some. by. Duncan. and. r ight. proce s s. mu s t. pathogene s i s horses .. Duncan. i nterpretat ion s ugge s t ive. of. obv i o u s. a xonal. losses. f i bre. results. form t he. the. the. be. in. approached. a nd. nerves. a l s o empha s i sed of in. the. ev idenced. author s. felt. the. chron i c. n a t ure. of. the on. only. that. a bnorma l i t i e s. r emy e l ina t i on. as. in. of. l a ryngea l hemipl eg i a. caut iou s l y. pre sence. i nvo l vemen t. any hypothe s i s. The. con f i rmed the. of. inc i dence. degenera t i on ,. pre s en t .. ba s i s. coworke r s. h i gh. t he. l a ryngeal. cond i t ion o f. demy e l i na t i on. mus t. f i bre. recurrent. a nd h i s. of. f ibre s ,. e spec i a l l y. of. � t a£ ( 1 97 8 ) ,. in. t e a s ed. pre sence. of. by. the. m a rked. that. the. tea sed. of. the. l e s i on ,. occ a s i ona l. act ive. demye l i na t i on . The. s i gn i f i cance. in. two c a s e s wa s. of. s imi lar. recurrent 1 968 ) . been. l aryngea l in. the. tape r i ng. d i s cu s sed with. f ind i n g s. They s een. of. as. a. nerve. s ta ted. that. of. rabb i t s. tape r i ng. a s s oc i a t i on. w i th. i nternod e s. r e s pe c t. f eature in. of. of. recu rrent. l a ryngea l. n erve s. ( W i l l i am s. a s c e nd i ng &. i nternod e s. c ompr e s s i ve the. the occurrence. the norm a l. i n gu i nea p i g s (Oc h oa & Marotte , 1 97 3 ) . ed. to. obs e rved. Kashef , ha s. nerve. a l so. l e s i on s. However , i n a f f e c t ­. tapered. i nternode s. were. not found in t h e r e g i on o f t h e aort i c a r c h where compre s s i on of. the. nerve. ( v..id� ..in/-/W ) .. has. been. s ugge s ted. as. a. pa thogen i c. f a c to r.

(42) 11. AETIOLOGY La ryng e a l known the. hem i p l e g ia. for. many. c o nd i t ion. been. a. g reat. hypot he s i s. is. year s , and. d isease. a nd. i ts. many. a. unknown. the. hor ses. becau s e. theor i e s. regard i ng. of. of. that. the. as. a e t i o logy. of. to. been. i mportance. pa t hogene s i s ,. o f fered. has. t here. have. cause .. Any. d i sease. mu s t. its. th i s. of. s a t i s f a c tor i ly expl a i n the va r i ou s c l i n i c a l and patho l og i c a l chara c t e r i s t i c s o f the cond i t i on . In a. l im i ted numbe r of. cause. is. produc e. read i l y. l e s ion s. cases. of. l a ryng ea l hemipleg i a ,. determ i ned .. Causal. et a l. per i v a s c u l a r. ,. 1 9 70a ). guttu r a l. myco s i s. 1 91 5 ;. Cook ,. 1 978 ;. Ro s e et a l ,. v i tam i n and. 1 95 1 ;. 1 976 ) ,. to. the. (Cook ,. 1 976 ) ,. l ead. (Loew , ( Hoa re ,. 1 964 ;. 1 91 5 ; &. Nea l. i nc r i m i na ted. s ugge s ted it. wa s. that. u n l ikely. in. that. N ew any. 1 972 ) ,. Cymbaluk. the s e. (Hoare , (Ro s e ,. (Hoare ,. 1 91 5 ) ,. et al ,. 1 977 ) ,. W i l l iam s ,. Ramsey ,. Z ea l a nd. of. � G i l bert ,. i ntox i c a t i on. the above f a ctors. the. (Mar k s. poi son ing. 1 97 3 ;. The s e i n c l ud e. neop l a s i a. o f 1 2 7 hor s e s w i t h laryngea l hemi p l e gi a , (1 981 b). can. inj e c t i on s. neck. organophosph a t e. po i s on i ng. S chebi t z ,. ( 1 9 8 1 u) .. perineural. 1 98 1 ) ,. de f i c i ency. plant. or. a c c i dent s. pou ch. wh i c h. o f t h e r e c urrent l aryngeal or vaga l nerves. we re out l i ned by Gou lden & Ander son irritant. factors. the. 1 945 ;. 1 972 ) .. In a. Kral , s tudy. Gou lden & And e r son in. only. env ironmen t f a c tors. were. 1 1 %. at. They least ,. important. i n the aet i o l ogy of mo s t ca s e s of t h i s d i sea s e . The. common ly. cons idered. c a u s e s o f the so ca l l ed i d i opa th i c. l arynge a l hem i p l e g i a can b e d iv ided into four ma i n group s : i ). Mechan i c a l cau s e s. ii ). Bact e r i a l or v i r a l agents. i. (ii i ). P l ant and chemi c a l i ntox i c a t i on s. ( iv ). V i ta m i n de f i c i en c i e s ..

(43) 12. In. add i t ion •i. c on s idered The s e. there to. are. a. number. pred i spose. i nc lude. breed ,. an. of. factors. i nd i v i d u a l. hered i ty ,. to. s i ze ,. w h i ch. t he. s ex ,. are. disease .. management ,. con f orma t ion , c l imate a nd geography . Each of. the pos s ib l e. cau s e s. i s d i sc u s s ed. i n the. f o l l ow i n g. page s .. Mechan i c a l c au s e s B IOMECHAN I CAL. THEORY. OF. STRETCH. TO. THE. LEFT. RECURRENT. LARYNGEAL NERVE Ten s i on. a nd. s tr e t c h o f the. recurrent. l a ryng e a l. nerve · have. l ong been cons idered r e levant to the a e t io logy of l a ryng e a l h em ip l e g i a of. thi s. (Ma rt i n ,. 1 8 87 ) .. s tretch i n g. heart. at. head. (Frank ,. s i t u a t i on s. exerc i s e. Hypothe s e s. i ncluded ; (Argy l e ,. 1 953 ) ;. (Cook ,. a. ba ckwa rd. 1 934 ) ;. a nd. the. dur ing growth (Ma r t i n ,. 1 8 87 ) .. In. De laney. 1 97 0 ,. t heory , b e i ng. Rooney. of. s tr e t ch. the. hypothesi s. a nd. cause was. to. the. of. equ ine. ba s ed. on. overext en s i on. of. the. of. of. the s e. i nc r e a s e o f neck. l en g t h. laryng e a l. c ou r s e as. tha t. and. due. l ength. to of. the the. left. c on s iderable. t en s i on. a. b i omecha n i c a l. l aryngea l. r e ga rd ing. nerve. the. Th i s nature ,. Rooney and De l aney. a natom i c a l. compared w i th the r ight ,. both. hem i p l e g i a .. i n c i dence and pa thol ogy of the d i s ea s e . concluded. cause the. recurrent. prem i s e s. the. of. po s t u l a t ed. left. to. movemen t. comb inat i on. 1 97 6 ) ;. as. d i f ferences. recurrent. in. l a ryngea l. the. nerve ,. the l e f t nerve i s p l a ced unde r. dur i n g. movement. of. the. neck .. They. cons ide red th i s ten s i on to be exacerba ted in the i nd iv idua l with a. l ong neck o r. l a rge. body ,. thu s. prov i d ing a n exp l a n ­. a t i on f o r t h e s i z e pred i spo s i t i on o f the d i s e a s e . to. Rooney. " ne ck i n g " b lood. and of. D e l aney. the. vessels ,. nerve. thi s and. r e s u l t ing. ten s i l e. f orce. c ompre s s i on in. va s c u l a r. of. Accord i ng. cou l d the. prod u c e. a s s oc i a t e d. i n s u f f i c i ency. and.

(44) 1 3. s ub s equ en� wou l d wa s. nerve. occur. in. node s ,. so. It. the m i dd l e. d i s cu s s ed. t en s i on. d amage .. by. exce s s ive. s t a ted that. th i rd of. could. the " ne ck i ng ". the ne rve .. R-i af.. ( 1 9 7 0 b ) ,. Mark s. produced. wa s. who. Th i s. theory. s ugge s ted. be exa cerba ted by e n l a r ge d. p e r i c a rd i a l. fat. or. backwa rd. that l ymph. d i s p l a cement. o f the hea r t . One. of. the. incorrect. present. a nd. p r i ma ry. s i te. of. to. a ctua l l y. occurred nerve" ,. in. De l a ne y. i n terpreted Cole. prem i s e s. i nterpre t a t i on. patho logy Rooney. ba s i c. the. not. the. to. middle. patho logy. prox i ma l ly ,. at. t h e d i s t r i bu t i on o f is. not. that. nerve theory. of. left. wou ld. in. m i dpo i n t. s tretch. to the. of. of. this. the. the. the. n e r ve s .. Co l e ,. the. nerve. nerve . ". is. Wha t. f i bro s i s. left. recurrent. both. d i sorder. of. Co l e ,. and. the left. can. e x t end. the ao r t i c arch .. Thus. l a r y ngea l nerve pa tho l o g y. expected. wa s. of. an. have shown that the d i s t a l. area. be. work. Moreover ,. ( 1 978 ). on. degenera t ion a nd. t h i rd .. to the. ( 1 946 ) ,. recurrent. t h i rd. t h e r ecurrent. wh i ch. at � i t s. the. i nv o l ve d. l a ryngea l. the. port i o n. o b se rved. l ea s t. on. " Ma rked. p e r i ph e r a l. work. r e c u r rent. i n the m idd le wa s ,. hypothe s i s. Co l e ' s. " Ba s ed. mor e recent l y Dun c a n R.i a f.. nerve. thi s. d i s ea s ed. s ta te ,. f ound. in. of. d amage. be. of. if. " ne c k i n g ". cause .. of. F u r thermore ,. r e c u rrent. l a ryng ea l. the thi s. n e rve. prov i d e s no exp l a na t i on for the patho l o g i c a l changes pre s en t in. the. R. i af.. ,. d i st a l. a. tha t. tens ion. pur e l y. m idpo i n t , way. r e c u r rent. l a ryngea l. nerve. ( Du n c a n. 1 978) .. From. at. r ight. two. is. on. the. mater i a l. the. a lso. po i nt s ,. at. mechan i ca l. &. nerve. s hou ld. b e i ng. the . l a rynx. " ne c k i n g " of. the. " n eck". of. p r e c i se. ( Al ex a nde r ,. wou ld. produce. i ncorre c t . p o i nt s , in. and. occur. Any. as. u n i f orm i t y. a. be. 1 974 ) .. the. " ne c k i n g ". m a t e r ia l middle. hypothe s i s. w h i ch. of. the. w i th. result. a r ch .. two. to g ive. l en g t h. beca u s e. l ength. of. of a ny. of. l a ryngea l. f i xed the. the. f i xed. po i n t s. •N everthe l e s s ,. o f · s t retch ,. pred i c t ed , the. the. at. is. tend. T h e recurrent. ao r t i c. a long. v i ew ,. ten s ion w i l l. the. th i s wa y , the. c annot. 1 98 1 ) .. not. K e r s haw ,. behave. does. of. w he n subj e c ted to. f i xed. ( S oden. nerve. point. when. locat ion the. lack. mater i a l.

(45) 1 4. Per iphera l. n erve s. s trength and and. characte r i s t i c a l ly. e l a s t i c i ty ,. prope r t ie s. of. the. 1 965 ) .. lea s t. mech a n i sms. c o n s iderable. t o the anatom i ca l a r rangement. componen t s. (Sunde r l a nd , t h re e. due. pos s e s s. Moreov e r ,. w i th i n. the. per i phera l. wh i c h. a l low. nerve. nerves. trunk. have. con s i de ra b l e. at. s t retch. to cccur. be fore d e form i t y o r patholog i c a l chang e s resul t .i .. F i r s t ly ,. the. the. who l e. surround i ng. descr ibe nerve. a. mechani s m s certain. c ourse. und u l ate. do. damage. c ro s s - s e c t i on a l. a rea. to. of. compr e s s i on. supply nerve. and. of. f i br e s. the. pe r i neur i um ,. The. site. of. i nterva l s. the. undu l a t i ng. f rom. cont en t s. nerve. is. and. t h i rd l y , the. the. the. th i s. to. h appe n s of. fascicle s ,. (Sunder land ,. ma y. at. the. b l ood. t e n s i on ,. a nd. l a ter. be. torn .. widely. 1 965 ) ,. a. l e a d i ng. incre a s i n g. be. these. beyond. decre a s e d ,. f a s c i c le s. t e nd s. W hi l e. impa i rment. W i th. w i th i n. ruptures. and. in. fascicles. stretch ,. When. ne rve. c ou r s e. nerve. f a s c i c le s .. o c c ur .. hence. the. nerve ,. the. condu c t i o n .. and the. the. nerve. the. r upture. t he s e. a long. the will. ne rve may. a l on g. of. an. S e cond l �. a l ong. protect. l im i t. pur s u e s. t i s sues .. wa vy. f i br e s. nerve. not. spaced at. the. l owe r i ng. the. midpo int a s wa s sugge s ted by Rooney & De laney ( 1 9 7 0 ) . Fac tors. whi ch. may j eopa rd i s e. nerve. f i bres. by. threshold at wh i c h s t re t ch beg i n s inc l ude adhe s i on s , changes in. the. conn e c t i ve. e l a s t i c i ty ,. ti s sues. of. the. nerve. that. decrea s e. and a n y deform i t y wh i ch impo ses a longer cou r s e. o n the nerve (Sunde r l and , 1 9 6 5 ) .. COMPRES S ION OF THE RECURRENT LARYNGEAL NERVE I N THE AREA OF THE AORTI C ARCH Mechan i c a l. d amage. to compr e s s i on ,. to. the. r e c u r rent. l aryngea l. nerve ,. has been men t i oned a s a cau s e o f. hemipl e g i a by a number of authors 1 838 ;. H a s l am , 1 8 9 3 ;. Ve rme u l e n ,. 1 93 4 ;. Hutyra e t a l , 1 9 3 8 ) .. (Bou ley , 1 8 2 5 ; 1 91 3 ;. due. l a ryngea l Fergu s s on ,. Hoa re , 1 9 1 5 ;. Argy l e ,.

Figure

TABLE 1 Experimental animal s

TABLE 1

Experimental animal s p.13
FIGURE 1

FIGURE 1

p.17
FIGURE 8

FIGURE 8

p.18
TABLE 1 :

TABLE 1 :

p.101
TABLE 2 :

TABLE 2 :

p.112
TABLE 3 :

TABLE 3 :

p.113
TABLE 5 :

TABLE 5 :

p.117
TABLE 6 :

TABLE 6 :

p.119
TABLE 7 :

TABLE 7 :

p.120
TABLE 8 :

TABLE 8 :

p.122
TABLE 9 :

TABLE 9 :

p.124
TABLE 1 0 : MUSCLE PATHOLOGY IN CONTROL HORSES ·

TABLE 1

0 : MUSCLE PATHOLOGY IN CONTROL HORSES · p.153
TABLE 1 1 :  MUSCLE . PATHOLOGY IN SUBC!JINICAL. tARYNGEAL HEHI'PLEGIC

TABLE 1

1 : MUSCLE . PATHOLOGY IN SUBC!JINICAL. tARYNGEAL HEHI'PLEGIC p.154
TABLE 1 2 :  MUSCLE PATHOLOGY IN CLINICAL LArtYNGEAI. HET-1IPI.EGIC·

TABLE 1

2 : MUSCLE PATHOLOGY IN CLINICAL LArtYNGEAI. HET-1IPI.EGIC· p.155
TABLE 1 3 :

TABLE 1

3 : p.169
Fig . 8 9 ,

Fig .

8 9 , p.176
TABLE 1 4 :

TABLE 1

4 : p.176
TABLE 1 5 :

TABLE 1

5 : p.177
TABLE 1 6 :

TABLE 1

6 : p.180
Table 1 7 .

Table 1

7 . p.182
Table 5 ) .

Table 5 )

. p.183
TABLE 1 8 :

TABLE 1

8 : p.184

References

Outline : NAL D I SCUSS I ON