Middle Ear Function in Learning-Disabled Children

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Middle

Ear

Function

in Learning-Disabled

Children

Forrest

C. Bennett,

MD, Susan H. Ruuska, MA,

and Roberta Sherman

From the Department of Pediatrics and the Child Development and Mental Retardation Center, University of Washington, Seattle

ABSTRACT. To investigate the possible association of

chronic otitis media and school learning problems, past and current middle ear status in 53 learning-disabled (LD) children was compared to that of56 control children without learning problems. A history of recurrent otitis

media was obtained in 23% of the U) children and in 9%

of the control children. Thirty-eight percent of LD chil-then and 16% of control children had hearing abnormal-ities on pure tone audiometry; 49% of LD children and 21% ofcontrol children had abnormal tympanometry. LD children had significantly more middle ear malfunction than control children. Chronic, undetected middle ear

problems may play a role in the etiology of some school

learning disabilities. Pediatrics 66:254-260, 1980; chronic

otitis media, learning disabilities,pure tone audiometry,

tynipanometry.

The etiology of school learning problems is often multifactorial and difficult to identify precisely. Central nervous system processing dysfunction, of-ten involving specific perceptual problems, is felt by many physicians and educators to be the major underlying determinant in learning disabilities.” However, a variety of constitutional and environ-mental factors have received attention as possibly contributing to the expression ofthis common prob-lem: family history, delayed neurologic maturation, temperament, pre-, peri-, or postnatal brain insult, chronic illness, anemia, undernutrition, food addi-tives, allergy, lack of parental stimulation, poverty, poor schools, and poor teachers.

A number of

reports

have appeared suggesting a relationship between chronic otitis media with mild, fluctuating hearing loss and disordered language development during childhood. That chronic mid-die ear disease may be an important factor in the

Received for publication March 13, 1979; accepted Nov 17, 1979. Reprint requests to (F.C.B) Department of Pediatrics, Univer-sity of Washington School of Medicine, Seattle, WA 98195.

American Academy of Pediatrics.

evolution of school learning disabilities also is cur-rently suggested but undocumented. We undertook this study to evaluate this proposed association between middle ear dysfunction and learning disa-bilities.

MATERIALS AND METHODS

All children participating in this study attended elementary school in the Shoreline school district, a suburban district adjacent to Seattle, with a total enrollment of about 11,000 students. The district has a homogeneous population ranging from middle to upper-middle class and is predominantly white. The senior author (F.B.) is the school physician for this district, and the second author (S.R.) is the district audiologist.

A total of 73 students in this school district, ranging in age from 7 to 12 years, attended full-time language and learning disability classes in one of four elementary schools during the 1977-1978 school year. To qualify for this special educational placement, these children had (1) demonstrated early school learning problems and (2) performed on psychological testing in the normal range on an inteffigence measure, but significantly below expec-tations on achievement, perceptual, and language measures. Utilizing class enrollment lists, all 73 learning-disabled (LD) children in the district were randomly matched on the basis of age, sex, and race with 73 control children who had no history of school learning difficulties and attended regular classes in the same elementary schools. Any child

with a known sensorineural hearing loss was

ex-cluded from the study. No child with a cleft palate or other craniofacial malformation predisposing to middle ear disease was included.

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question-hi

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sr. 5/511

21.4% 112/511

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(5/513 naire concerning the frequency of past ear

infec-tions in their child. Parents who did not respond to this letter were contacted by telephone as a re-minder to return the consent form. The families of 53 learning disabled children (37 boys, 16 girls; mean age 10 years 5 months) and 56 control children (41 boys, 15 girls; mean age 10 years 3 months) agreed to participate in the study. The greater than 2:1 ratio of boys to girls is typical of learning disa-bility classes and clinics evaluating children with language and learning problems.

These 109 children were evaluated audiologically by one of the authors (S.R.) during the months of February, March, and April 1978. All were individ-ually evaluated at their own school in sound-treated rooms suitable for pure tone testing.

Learning-dis-abled and control children were examined in ran-dom order at all schools so that the audiologist was unaware of the academic status of the individual child. If, for any reason, a study child was absent from school on the day of testing or presented for testing with an upper respiratory infection, he or she was then evaluated at a later makeup time.

Each child was initially examined with an oto-scope to document patency of the ear canals. Any child found to have sufficient cerumen in the exter-nal auditory canal to potentially interfere with op-timal testing was evaluated after resolution of the problem. Because several observers performed this preliminary examination and because of the known interobserver variabifity in evaluating the presence or absence of subtle middle ear pathology, clinical assessments of middle ear function were not stan-dardized or compared in this study.

Following this quick screen, the child was given a five-frequency (250, 500, 1,000, 2,000, 4,000 Hz or cps) pure tone audiometric screen at an intensity of

20 dB (American National Standards Institute cal-ibration, 1969). Any student failing this screen, ie, missing any frequency at 20 dB, was given a com-plete bilateral threshold examination with results recorded on an audiogram. Finally, each child re-ceived bilateral tympanometry with the Madsen impedance audiometer (model ZS76-I) with results recorded on a tympanogram. Tympanograms were plotted manually on the basis of readings obtained at intervals of 50 mm H20 over a pressure range of +200 to -400 mm H20. Peak locations that fell between the 50-mm demarcations were ascertained within 20 mm.

RESULTS #{149}

Otitis Media History

Since parental recollection of the exact number of acute ear infections sustained by their child may well be inaccurate, we were primarily interested in concentrating on children who clearly had a history

of recurrent otitis media. Howie et al3 in 1975 de-scribed the “otitis-prone” condition and included children who had six or more episodes of acute otitis media before age 6 This frequency of disease was used to define our recurrent otitis rnelia group. In fact, six infections was a logical dividing point, because the majority ofour children fitting into this group had many more than six infections with

pa-rental comments such as “all the time,” “every

month,” and “always on antibiotics?’

A history of recurrent otitis media during child-hood was obtained for significantly more learning-disabled children than control children. Twelve of 53 learning-disabled children (23%) and five of 56 control children (9%) had recurrent infection by history

(P

< .05).

Pure Tone Audiometry

For the purposes of this study, an audiogram was considered abnormal when a unilateral or bilateral

hearing loss of greater than 20 dB was

demon-strated. Some pediatric audiologists active in the investigation of language development would ac-tually lower the threshold of concern to 10 or 15 dB, but this remains an issue of controversy.4 We chose the 20-dB threshold because it is a more conserva-tive level and is the widely accepted level for audi-ologic screening Of school age children. All abnor-mal audiograms in this study were most likely in-dicative of a conductive hearing loss, since children in

this

school district have annual audiologic eval-uations, and those demonstrating a selective,

high

frequency hearing loss were excluded from this investigation.

The result of threshold audiometry is shown in the first histogram of Fig 1. Significantly more

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Aidusgias Tyausas ad Tyaia.s

Fig 1 . Prevalence of abnormal audiometry, abnormal

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learning-disabled than control children demon- control) had functioning tympanostomy tubes in strated an abnormal audiogram (20/53 or 38% as place and were not included in the abnormal tym-opposed to 9/56 or 16%;

P

< .05). Fig 2 shows that panogram data. Thus, slightly more than 50% of the of the 20 learning-disabled children with abnormal learning-disabled children evidenced some type of audiograms, 13 were unilateral and seven were bi- middle ear dysfunction.

lateral. Of the nine control children with abnormal- Fig 3 ifiustrates the frequency ofthe four different ities, five were unilateral and four were bilateral. types of tympanogram obtained in this study. The Ten of these learning-disabled children’s hearing tympanogram data are based on the number of losses were equal to or greater than 30 dB in one or children demonstrating each type of curve and not both ears compared to five of the control children’s on the total number of ears. A child with one normal

losses. and one abnormal curve was classified according to

the type of abnormal tympanogram. Only four

chil-Tympanometry dren had mixed results with two different types of

Utilizing Jerger’s classification,5 tympanograms abnormal tympanogram; these children were clas-sified according to the more abnormal type. In fact, were divided into four types Type A was considered

the configuration of Fig 3, when considering the a normal tympanogram, and all other types were

total number of ears, is virtually identical to the interpreted as abnormal. Type A,, (decreased

com-displayed figure. pliance) is generally associated with a heavily

thick-Of special interest is the striking predilection for ened or scarred tympanic membrane; type B

(non-mobile tympanic membrane) with middle ear effu- negative pressure tympanogram (type C) in the learning-disabled children. Furthermore, of the 19 sion or tympanic membrane perforation; type C

children with type C tympanograms (16 learning-(negative pressure) with eustachian tube

dysfunc-disabled vs three control), 15 demonstrated signifi-tion and possible middle ear effusion. The presence

cant abnormality with a negative pressure of 2#{174} of effusion in type C tympanograms has been

re-mm H20 and/or a compliance of6 units (arbitrary lated to the degree of abnormal middle ear pressure

Madsen compliance units based on a 0 to 10 scale and the magnitude of decreased compliance.

Ac-cording to Paradise et al,6 low-peaked, negative with higher numbers indicating reduced

compli-ance) and thus were most likely to be associated pressure tympanograms are much more likely to with middle ear effusion.6 Of these 15 children 13 indicate chronic serous or secretory otitis media were in the learning-disabled group

(P

< .01). Seven than high-peaked, negative tympanograms. of these 13 learning-disabled children had type C

As can be seen in Fig 1, acoustic impedance

measurement revealed 26 learning disabled children tympanograms with both high negative pressure and reduced compliance, five had high negative (49%) as compared to 12 control children (21%) with

pressure with average compliance, and one had

an abnormal tympanogram in one or both ears (P

reduced compliance with moderate negative pres-< .01). Four children in this study (three LD, one

sure. Of the two control children with significantly abnormal type C tympanograms, one had both high negative pressure and reduced compliance and the

LeaIoi.f Sisabled other had high negative pressure with average com-Cd* a 531 pliance.

n

Centisi ChiIdeu

Fig

1 shows that 16 learning-disabled children

L____JI’ 511

(30%) as compared to five control children (9%) had both an abnormal audiogram and an abnormal tym-panogram

(P

< .01). Thus, of the 26 learning-dis-abled children with abnormal tympanometry, 62%

. (16/26) also demonstrated a hearing loss compared

to 42% (5/12) of the control children with abnormal tympanometry. Examining the data in another way, 18

hO 53) of the 20 learning-disabled children with abnormal

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. withnostomyaudiometry,abnormaltubes)19 showedtympanometry,compared middleto five earthreeof thedysfunctionwithnine tympa-control(16 CIIlreu .db 3111

I,” m sit i bith children with abnormal audiometry.

“Is It should be noted that ofthe 16 learning-disabled children with type C tympanograms, 12 also had a hearing loss; of the five with type B tympanograms, two had a hearing loss; of the five with type A,

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Fig 3. Frequency of different types of tympanogram in

learning-disabled and control schoolchildren. Four chil-dren (three LD, one control) are not included because of

tympanostomy tubes.

tympanograms, two had a hearing loss. In compar-ison, none of the three control children with type C tympanograms also had a hearing loss; four of the five with type B tympanograms and one of the four with type A8 tympanograms had a concurrent hear-ing loss.

Ofthe 12 learning-disabled children with histories of numerous, recurrent middle ear infections, nine demonstrated decreased hearing on their audi-ograms, eight had abnormal tympanometry, and three (not included in the tympanometry data) had

tympanostomy tubes in place. Thus, only one of

these 12 children had normal middle ear function as measured by tympanometry at the time of this study. In contrast, of the five control children with

past histories of recurrent otitis media, none dem-onstrated a current hearing loss, and only two had abnormal tympanograms. Of children in this study with early, recurrent otitis media, those who devel-oped learning disabilities were much more likely to also show evidence of persistent middle ear dys-function than were those children who had no spe-cial learning problems.

DISCUSSION

Does the common childhood malady of middle ear dysfunction, as manifested by chronic and re-current otitis media with middle ear effusion, pre-dispose children to the later development of lan-guage and/or learning problems? This important question is not new in the pediatric or otologic literature, but is currently receiving increased at-tention because of the marked prevalence of, and the controversies regarding the treatment of, both conditions, ie, chronic otitis media and school

learn-ing problems. With the provocative hypothesis that early, chronic otitis media with mild, fluctuating

hearing loss can have deleterious, irreversible

aca-demic sequelae-an hypothesis receiving wide-spread dissemination in the popular press

(News-week, June 14, 1976, p 97)-some otologists and audiologists presently advocate a very early, vigor-ous medical, surgical, and educational approach to this problem including liberal hearing aid

place-ment and home stimulation programs for young

children with recurring middle ear disease With the coincident development ofimpedance audiome-try technology and thus the potential for early identification of middle ear dysfunction comes the possibility of large-scale screening programs for young children, which would lead to early interven-tion in this disease process and would hopefully prevent the presumably associated developmental and psychoeducational disabilities. With all of this current activity, it is probably not surprising that a cause and effect relationship is automatically as-sumed by many today. Northern8 states in a recent review advocating broader use of impedance audi-ometry: “the best way to avoid these educational problems (ie, learning disabilities) is to utilize better techniques to identify children with middle ear effusions as early as possible so that treatment can be initiated.” Downs7 would grant syndrome status to this entire problem and has coined the label irreversible auditory learning disaster (lAID) for children suffering the presumed educational com-plications of early otitis media.

What is the accumulated research evidence for a significant association between chronic otitis media and school learning problems? Initial scattered re-ports, principally in the audiologic literature, failed to attract much widespread interest. As early as

1935, Bond9 reported on a sample of 128 children in New York City schools and noted that hearing loss

was about 15 times more common among children who were having reading problems than among

those whose reading skills were normal. The

con-troversial British psychologist, Cyril Burt,’#{176}re-ported a similar study from England in 1950. In groups of children with normal educational attain-ments 4% demonstrated a mild hearing loss, whereas among groups of children failing in school, 12% to 18% showed a similar hearing loss. In 1956 the Scottish Council for Research in Education made an analysis of the results of school transfer examinations on 310 children aged 11 to 12 years, all ofwhom had a history ofotitis media.” Children in this group were significantly educationally re-tarded relative to children with a history of normal hearing. Moreover, achievement declined in rela-tion to the severity and duration of hearing loss.

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widely divergent social backgrounds and since both chronic otitis media and school problems occur more commonly in lower socioeconomic status chil-dren, Ling’2 controlled for social class and home environment in a 1959 unpublished research thesis comparing two groups of English school children attending regular classes, one group with histories of otitis media and a mean 25-dB hearing loss and the other without such problems. In this

well-de-signed, small study he found the hearing-impaired

group to be more than one year behind the control group on several academic achievement measures by 10 years of age.

A decade passed before a resurgence of interest in the possible developmental consequences of chronic otitis media occurred. A group of studies then appeared involving various unique populations of children and focusing primarily on language de-velopment. Holm and Kunze’3 studied retrospec-tively a small group of children with chronic otitis media and fluctuating hearing loss who were cared for at a hospital-based ear-nose-throat clinic and compared them to children attending other hospital clinics. The study group was significantly delayed in all language skills requiring the receiving or pro-cessing of auditory stimuli or the production of verbal responses. No analysis was made of these children’s actual school functioning. Paradise’4 compared language function in two groups of

chil-then with cleft palate, one vigorously managed from early infancy to control middle ear effusion and the other more conservatively handled with long pe-riods of untreated effusion. The group with

nonef-fusion (and thus presumedly normal hearing) had

significantly better language development; school achievement was not reported. Lewis’5 studied Aus-tralian aboriginal schoolchildren, a culturally dis-advantaged group with a high prevalence of otitis

media, and found a subgroup with chronic otitis

media to be deficient in a variety of auditory pro-cessing skifis as compared to a subgroup with nor-mal middle ear function. Again, no differences in school performance were reported.

Three recent investigations have addressed the specific issue of real school learning problems, as opposed to statistical deficiencies on complex speech and language tests, following chronic otitis media. Kaplan et al,’6 reported a ten-year follow-up study on a large cohort of Alaskan Eskimo children, another group with a high prevalence of otitis me-dia. Children with a history of otitis media prior to 2 years of age and a hearing loss of 26 dB or greater had significant deficits in both language skifis and school achievement (reading and math) and were more likely to have experienced grade retention in

school. The number of otitis media episodes was

related to tympanic membrane abnormalities,

hear-ing loss, and low verbal and achievement scores. Zinkus et al’7 investigated a group of children re-ferred to a university child development clinic be-cause of school underachievement. He identified two subgroups, one with a history of early, chronic otitis media and the other without middle ear prob-lems. Children with chronic otitis media showed substantial delays in speech and language, auditory processing, and reading and spelling skills. The authors recommend early medical and educational intervention for children with chronic otitis media and language delay as a possible strategy for pre-venting the development of a specific learning dis-ability. Finally, Masters and Marsh’8 described a significantly higher incidence of middle ear pathol-ogy as determined by tympanometry in learning-disabled school children than in their regular class peers. This study did not assess current hearing status nor historical evidence of chronic otitis me-dia.

The present study confirms and expands upon Bond’s original 1935 report. We found in a white, middle-class, elementary school population (1) a significantly increased incidence of recurrent otitis media among children with documented language

and learning disabilities; (2) significantly more

on-going middle ear dysfunction as evidenced by mild hearing loss and abnormal tympanometry among

learning-disabled children; and (3) a disturbingly

high proportion of young learning-disabled children with evidence of active, unrecognized middle ear problems.

More than 50% of the learning-disabled children in this study manifested abnormal tympanometry, pure tone audiometry, or both. In evaluating this high prevalence, it should be emphasized that this study was conducted in early spring (well after the

Seattle peak of midwinter respiratory disease);

chil-dren with evidence of acute respiratory infection of any type were not tested while ifi, and the 20 learning-disabled children whose families did not agree to their participating in the study might be assumed to be at even greater risk for undetected medical problems.

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amount of lumping together of abnormal

audi-ograms and abnormal tympanograms occurred in

the data analysis. It should not be concluded that all audiograms and tympanograms designated ab-normal were equally so or have equal clinical sig-nificance. Type B and type C tympanograms imply different degrees of middle ear dysfunction as does a unilateral 25-dR hearing loss vs a bilateral 40-dB loss. Nevertheless, our primary purpose was to com-pare learning-disabled and regular class children,

and

on all measures we found significant differ-ences.

A causal relationship between chronic otitis me-dia and schoollearning problems cannot be inferred from our retrospective data. However, the evidence certainly suggests an association between these two disorders and supports the recent observations of Masters and Marsh.’8 Moreover, an additional chin-ical implication of this investigation is the identifi-cation of a high risk group, ie, language- and learn-ing-disabled children, for long-term

vigilant

moni-turing and management of chronic middle ear

dis-ease. Despite the appropriately conservative posi-tion of the Task Force on Impedance Screening for Children on mass tympanometry screening in pub-lic schools,’9 learning-disabled children may well

comprise an especially vulnerable subgroup, in

whom serial tympanometry, performed in school, could provide early recognition of such chronic middle ear dysfunction which may be further com-pounding these children’s learning difficulties.

Finally, it should be emphasized that this study in no way implicates the periodic bouts of acute otitis media with transient hearing loss experienced by many children during the early years of rapid language development as important in the patho-genesis of later school learning problems. Rather, this study should serve to reinforce the clinical observation that children with chronic middle ear dysfunction and associated fluctuating hearing loss are at increased, but not inevitable,

risk

for chronic

language

and learning disabilities. This important

distinction is best made by the marked difference in current middle ear function between learning disabled and control children with histories of re-current otitis media. These learning-disabled chil-dren demonstrated continuing, persistent middle

ear problems and hearing loss, while children with

similar past histories but without learning problems had no ongoing hearing loss and very little middle ear dysfunction.

IMPLICATION

Does chronic otitis media, with fluctuating hear-ing loss during infancy and childhood, frequently cause language and learning problems in

neurolog-ically intact children of average inteffigence reared in supportive and stimulating home environments? The present study does not answer this key ques-tion, nor is it definitively answered by the reviewed previous research efforts. As pediatricians, we can all anecdotally cite many children with chronic otitis media who talked early and are thriving in school. A search of the literature reveals no long-term, rigorously controlled (ideally with siblings) prospective study of a middle-class pediatric popu-lation in which emerging language and learning function of children with chronic and recurrent otitis media is compared to that of their nonotitis controls. Paradise’4 has recently called for this type of investigation, and we are in the early phase of such an effort within a health maintenance organi-zation. In the meantime, what seems to be clear from our study and the combined work of others is that chronic middle ear dysfunction may be a sig-nificant additional factor in the etiology of language

and learning disabilities, particularly in children

already at constitutional and environmental risk for development of these multifactorial problems.

ACKNOWLEDGMENT

This investigation was supported in part by Maternal and Child Health Services, Bureau ofCommunity Health Services, Health Services Administration, Department of Health, Education and Welfare, Project No. 913.

REFERENCES

1. Chalfant JC, Scheffelin MA: Central Processing

Dysfunc-tion in Children: A Review ofResearch. MINDS Monograph

No. 9, Bethesda, Maryland: US Dept of Health, Education, and Welfare, 1969

2. Silver LB: Acceptable and controversial approaches to treat-ing the child with learning disabilities Pediatrics 55:406,

1975

3. Howie VM, Ploussard JH, Sloyer J: The “otitis-prone” con-dition. Am J Dis Child 129:676, 1975

4. Downs MP: Hearing loss: Definition, epidemiology and pre-vention. Public Health Rep 4:255, 1975

5. Jerger JF: Clinical experience with impedance audiometry.

Arch Otolaryngol 92:311, 1970

6. Paradise JL, Smith CG, Blueatone CD: Tympanometric detection of middle ear effusion in infants and young chil-dren. Pediatrics 58:198, 1976

7. Downs MP: The expanding imperatives of early identifies-tion, in Bess PH (ed): Childhood Deafness. New York, Grune & Stratton, Inc, 1977, pp 95-106

8. Northern JL: Advanced techniques for measuring middle ear function. Pediatrics 61:761, 1978

9. Bond GL: Auditory and Speech Characteristics of Poor

Readers, Teachers contribution to education No. 657. New

York, Teachers College, Columbia University, 1935 10. Burt C: The Backward Child. London, University Press,

1950

11. Scottish Council for Research in Education: Hearing Defects

in School Children. London, University London Press, 1956

12. Ling D: Rehabilitation of cases with deafness secondary to otitis media, in Glorig A, Gerwin KS (eds): Otitis media:

Proceedings of the National Conference, Callier Hearing

and Speech Center, Dallas, Texas. Springfield, IL, Charles

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13. HoIm VA, Kunze LH: Effect of chronic otitis media on language and speech development. Pediatrics 43:833, 1969 14. Paradise JL: Pediatrician’s view of middle ear effusions: More questions than answers. Ann Otol Rhinol Laryngol 85 (suppl 25):20, 1976

15. Lewis N: Otitis media and linguistic incompetence. Arch

Otolaryngol 102:387, 1976

16. Kaplan GJ, Fleshman JK, Bender TR, et al Long-term effects of otitis media: A ten-year cohort study of Alaskan

Eskimo children. Pediatrics 52:577, 1973

17. Zinkus PW, Gottlieb MI, Schapiro M: Developmental and psychoeducational sequelae of chronic otitis media. Am J

Dis Child 132:1100, 1978

18. Masters L, Marsh GE: Middle ear pathology as a factor in learning disabilities. J Learning Disabilities 11:103, 1978 19. Task Force of the Symposium on Impedance Screening for

Children: Use of acoustic impedance measurement in screen-ing for middle ear disease in children. Pediatrics 62:570, 1978

OBSTETRIC RADIOGRAPHY AND CHILDHOOD MALIGNANCY

A much improved reanalysis of data from the Oxford Survey of Childhood Cancer reveals once again that after obstetric radiography, the estimate for the child’s relative risk of cancer is 1.47 overall, and does not vary significantly between different tumor groups, for different ages at death, or between the sexes

(Blithell JF, Stewart AM: Br J Cancer 31:271, 1975). The most interesting new information is that the

risk

declined over time comparably for: (a) hematopoietic tumors and (b) solid tumors, as the number and dose of x-ray exposures diminished. The effect persisted when various possible confounding epidemio-logic factors were taken into account, particularly the number of illnesses suffered by the mothers of the 8,513 cases as compared with matched controls.

(There is nothing wrong with the logic, as reasoned from the data. Some

investigators will still wonder, however, on the basis of what is known about the

dissimilar epidemiologic characteristics of various childhood cancers, why each

of them has the same increase in relative risk after diagnostic exposures to x-ray

during intrauterine life. The authors do not mention that in a study by S.

Graham et al, the same effect was found when irradiation occurred before conception [Graham 5, et al: NCI Monogr 19:347, 1966], and in another study, when obstetric radiation was administered, there was a similar increase in the relative risk for nonmalignant causes of death, including accidents and

respira-tory disorders [Diamond EL, Schmerler H, Lilienfeld AM: Am J Epidemiol 97:

283, 1973]. Is it possible that the method ofstudy somehow increases the relative risk, regardless of the disorder studied?)

Robert W. Mifier, MD

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1980;66;254

Pediatrics

Forrest C. Bennett, Susan H. Ruuska and Roberta Sherman