International Journal of Pediatric Otorhinolaryngology, 3 (1981) 129-135 @ ElsevierlNorth-HoIIand Biomedical Press

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AUDIOLOGICAL FINDINGS OF PATIENTS WITH ACHONDROPLASIA

LILLIAN GLASS *, IRVING SHAPIRO, SUSAN E. HODGE, LAVONNE BERGSTROM and DAVID L. RIMOIN

Los Angeles County-University of Southern California Medical Center, Genetics Division, Los Angeles, Calif,; (S.E.H.) Neuropsychiatn’c Institute and (L.B.) Division of Head and Neck Surgery, Center for Health Sciences, UCLA Medicat Center, Los Angeles, Calif.; (IS.) Center for Communication Disorders and (D.L.R.) Division of Medical Genetics, Harbor-UCLA Medical Center, Torrance, Calif. (U.S.A.)

(Received June 2nd, 1980) (Accepted September 22nd, 1980)

INTRODUCTION

Skeletal dysplasias are a heterogeneous group of disorders which result in short stature and skeletal deformities. To date there are over 70 distinct recognizable conditions [15]. With the exception of two recent studies on patients with osteogenesis imperfecta [2,14] and Morquio syndrome [ 131, audiological evaluation on skeletal dysplasia patients have not been system- atically obtained. In most cases data consist of casual observations, which were done on small numbers of patients where types of hearing loss and ranges or variability in hearing levels were not differentiated.

This is particularly evident in discussion of audiologic status of patients with achondroplasia. Achondroplasia is an autosomal dominant skeletal dys- plasia characterized by short stature, short limbs, and a variety of cranio- facial abnormalities including a shortened cranial base, frontal bossing of the skull, and numerous dentofacial abnormalities. Gorlin et al. [ 6 ] and Cohen [3] reported a high incidence of otitis media in patient with achondroplasia. Hall 171, in a survey of 150 achondroplasts over the age of 18 years found that 75% reported having had ear infections and 11% reported that they ended up with a significant hearing loss. Glass et al. [5] in a study of 88 achondroplasts, found that 97% of the subjects reported having a history of ear infection and/or hearing loss. On pure-tone audiometric screening, 72% of the achondroplasts were found to have a hearing loss of 22 dB (ANSI- 1968) or greater.

Based on these data the following questions arose. (1) Do achondroplasts have a higher incidence of hearing loss than other skeletal dysplasias? (2) What type of hearing loss is characteristic in achondroplasia? (3) What are

* Address for reprints: IG-24 Genetics Division, LAC-USC Medical Center, 1129 N. State St., Los Angeles, Calif. 90033, U.S.A.

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the middle ear electroacoustic impedance function characteristics of achon- droplasia?

This investigation systematically describes audiologic characteristics and middle ear function in achondroplasia.

METHODS

Subjects Twenty-eight subjects (15 male, 13 female) with a clinical diagnosis of

achondroplasia and 10 subjects with clinical diagnoses of some other skeletal dysplasias (OSD) who did not have craniofacial abnormalities (2 pseudo- achondroplasia, 3 hypoachondroplasia, 1 spondylometaphyseal dysplasia, 3 cartilage hair hypoplasia, and 1 hypopituitary dwarf), were randomly selected from the patient caseload at the Harbor-UCLA Short Stature Clinic. Subjects ranged in age from 20 months to 63 years with a mean age of 19 years, 7 months. The age distribution of these short statures is shown in Table I.

Procedure Air-conduction, bone-conduction, speech reception thresholds and speech

discrimination scores were obtained on all subjects. Pure-tone air- and bone- conduction thresholds were obtained in accordance with the guidelines that manual pure-tone air-conduction thresholds of 20 dB HL or greater at two or more frequencies in the frequency range of 250-8000 Hz in one or both ears were considered to have hearing loss. If the difference between air-con- duction and bone-conduction thresholds in the frequency range of 500- 4000 Hz exceeded 10 dB, a conductive involvement was considered to be present.

In addition, middle ear electroacoustic impedance function studies con- sisting of dynamic and static compliance and contralateral acoustic reflex were obtained on all 38 subjects. The 6 youngest subjects (age range 20-36 months) were evaluated using sound field COR audiometry [ 161.

TABLE I

DISTRIBUTION OF AGES BY CLINICAL DIAGNOSIS

Age range in years Achondroplasia Other skeletal dysplasias

O-10 7 11-20 12 21-30 4 31-40 3 41-50 0 51-60 0 61-70 2

Total 28

3 5 1 0 1 0 0

10

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Equipment All hearing tests were performed by one of the investigators in one of two

audiometric test suites (IAC 1400 series). Pure-tone and speech audiometry were conducted on either a Maico MA-24 or a Beltone 200C audiometer both of which were calibrated to ANSI-1969 reference levels. Middle ear electroacoustic impedance function studies (dynamic and static compliance and acoustic reflex thresholds) were obtained with either a Madsen 20-73 or 20-70 Electra-Acoustic Impedance Bridge. A Zenith ZA 1lOT portable audiometer, calibrated to ANSI-1969 reference levels, produced the auditory stimuli for determination of the acoustic reflex threshold when the 20-70 impedance bridge was used. The output and response characteristics of the equipment were monitored on a regular basis and were stable throughout the course of the study.

Speech audiometry material included the CID W-l list and the NU 6 Audi- tory Test Lists B, C, and D recorded on reel-to-reel tape by Auditec of St. Louis (402 Pasadena Avenue, St. Louis, MO., 63119). Speech tests were presented via the tape playbacks associated with the two clinical audiometers. For three children speech audiometry was performed using selected spondees and PBK word lists presented via monitored live voice.

RESULTS

Table II shows the distribution of hearing loss in the 28 achondroplasts and in the 10 OSDs. A x2 test of independence was performed with x2 = 4.89, significant at P < 0.05. Thus, it appears that achondroplasts had a greater incidence of hearing loss than other skeletal dysplasias in this sample.

The types of hearing loss characteristic in achondroplasia are shown in this table. It appears that achondroplasts commonly had conductive hearing loss. Thirteen subjects had conductive loss in at least one ear. Seven had sensori-

TABLE II

TYPES OF HEARING LOSS IN ACHONDROPLASTS AND IN OTHER SKELETAL DYSPLASIS

Affected ears of subjects and type of loss

Achondroplasia (n = 28)

Other skeletal dysplasias (n = 10)

Both ears, sensorineural 1 1 sensorineural, 1 conductive 4 1 sensorineural, 1 normal 2 Both ears, conductive 6 1 conductive, 1 normal 3 Both ears normal 11 Both ears mixed 1

Total no. patients showing hearing loss 17

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133

neural loss in at least one ear and one subject had a mixed loss in at least one ear. The number of OSDs examined was too small to draw statistical con- clusions regarding the type of hearing loss.

Table III shows the mean air-conduction and bone-conduction thresholds for the right and the left ears for achondroplasts and OSDs for both air- and bone-conduction, respectively. This table suggests that achondroplasts tend to have poorer hearing abilities than the OSDs. However, a t-test on the dif- ferences of the means cannot be performed, due to the large differences between the variances of the achondroplasts and the OSDs. Further inspec- tion of the table indicates that achondroplasts have poorer air- and bone-con- duction thresholds in the right ear than in the left ear.

Table IV shows the results of middle ear electroacoustic impedance func- tion studies of achondroplasts and OSDs according to the tympanogram types described by Jerger et al. [ll]. Dynamic compliance describes the changes in eardrum compliance as air pressure in the external ear canal is varied. The results of these changes are plotted on a graph (tympanogram) as compliance versus air pressure. Jerger [lo] described the major types of tym- panograms. In type A, the compliance peak is observed at or near ambient air pressure (0 mm Hz0 equivalent pressure). This type is found in normal and otosclerotic middle ears. Type B, where there is no significant observable change in compliance over the range of air pressure changes, is most com- monly seen in ears with otitis media. Type C describes the tympanogram which shows normal eardrum compliance, but the compliance peak is more negative than 100 mm Hz0 pressure, and describes negative pressure in the middle ear. Two sub-categories of type A tympanograms were noted by Jerger et al. [ll]. The type As tympanogram is where the peak compliance is at normal air pressures but at lower than normal compliance values; type An describes the finding where the peak compliance is at normal air pressure but the compliance is greater than normal It is important to note that these

TABLE IV

PERCENTAGE OF TYMPANOGRAM TYPES AND ACOUSTIC REFLEX RESPONSE

Tympanogram type Achondroplasia Other skeletal dysplasias (n = 46 ears) (n = 20 ears)

A

As AD B C

Acoustic reflex Normal Elevated Absent

48% 6% 4%

24% 17%

22% 17% 61%

70% 10%

0% 10% 10%

80% 5%

15%

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are the types of pathology that are described, but the tympanogram is not the proof of the pathology.

Static compliance refers to the compliance of the middle ear in the plane of the eardrum and is computed by subtracting the air volume of the exter- nal ear canal from the combined equivalent volumes of the external ear canal and middle ear. This is expressed in cubic centimeters (ml) [ 111.

The acoustic reflex threshold is the lowest intensity level of an auditory signal that produces an observable change in the compliance when the tone is presented to one ear and the probe tip of the impedance bridge is inserted into the opposite ear [ 111.

Approximately 51% of achondroplast ears had abnormal middle ear func- tion, while 30% of the OSDs did. It is interesting to note that 24% of the achondroplasts had a type B tympanogram, which describes an immobile tympanic membrane, and 17% had a type C tympanogram, which is indica- tive of Eustachian tube dysfunction. Table III also describes the acoustic reflex thresholds in achondroplasts and OSDs. For the purposes of this study, normal acoustic reflex thresholds are those less than or equal to 100 dB HL. Elevated thresholds are greater than 100 dB HL. If no acoustic reflex is observed at 125 dB HL, it is considered to be absent. Abnormal acoustic reflex findings were evident in 78% of achondroplasts as opposed to 20% of the OSDs. The static compliance which describes the contribution of the middle ear to the overall acoustic impedance was found to be within normal limits for both groups (achondroplasts = 0.58 f 0.48 ml, OSD = 0.58 f 0.31 ml).

The mean speech receptor thresholds (SRT) for achondroplasts and OSDs were in good agreement with the pure-tone averages for both ears. The mean speech discrimination scores (SDS) for both groups were within normal limits.

All 4 achondroplasts tested using COR audiometry were found to have normal hearing. On electroacoustic impedence function studies, one had abnormal tympanometry and one could not be evaluated due to the presence of PE tubes. Two had normal tympanometry.

DISCUSSION

The high incidence of hearing loss among the achondroplasts might be attributed to altered craniofacial morphology. Of the 5 patients with sensori- neural hearing loss, one patient, a 63-year-old female, had an acoustic tumor. One 61-year-old female had a tympanoplasty and subsequently a mastoi- dectomy in the right ear. Two l&year-olds had unexplained low frequency sensorineural hearing losses.

Six of the 24 achondroplasts had normal hearing as determined by pure- tone threshold audiometry and abnormal electroacoustic impedance func- tion studies. This supports the impression that middle ear impedance studies

135

may be a more sensitive measure of middle ear status than pure tone thres- hold audiometry.

Thorough and comprehensive examination of hearing abilities of children with achondroplasia may help forestall subsequent problems in speech and language development as there is evidence in the literature which suggests that fluctuating conductive hearing loss contributes to a delay in speech and language development [4,9,12].

Inasmuch as the causes for the greater incidence of hearing loss among the achondroplasts are not yet clearly understood, further detailed clinical investigation, including otologic and radiographic evaluation, appears to be warranted.

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12 13

14

15

16

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