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

(1)Copyright is owned by the Author of the thesis. Permission is given for a copy to be downloaded by an individual for the purpose of research and private study only. The thesis may not be reproduced elsewhere without the permission of the Author..

(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 ,.