IMPEDANCE MEASUREMENTS IN THE DIAGNOSIS OF MENIERE'S DISEASE LINDA LLOYD, B . A . ( S p . & H . T H E R A P Y ) ( W I T W A T E R S R A N D ) Speech Therapy Department, Groote Schuur Hospital Cape Town SUMMAR Y Meniere's disease is discussed in terms of diagnostic difficulties, histological findings and treatments pointing to the use of impedance techniques with this condition. Ten subjects were given a questionnaire, regarding the symptoms experienced at the time of testing and impedance measures were conducted. Acoustic impedance values were higher in 80% of the affected ears when compared to the unaffected ears. Four of these values were more than double those in the unaffected ears and three were above normal limits. Therefore, increased endolymphatic pressure appears to be reflected in the test results. It is felt that impedance techniques should be.included in the test battery for the diagnosis of Meniere's disease. OPSOMMING Meniere se sindroom word behandel in terme van diagnostiese probleme, histologiese bevindings en behandeling en dui.op die gebruik van impedans- tegnieke vir hierdie toestand. Aan tien proefpersone is daar 'n vraelys uit- gedeel aangaandedie simptome wat ervaar is tydens toetsing en 'n opname van impedansmetings is gemaak. Akoestiese-impedans waardes was hoer in 80% van die aangetaste ore in vergelyking met die onaangetaste ore. Vier van hier- die waardes was meer as dubbel vergelyk met die van die onaangetaste ore, en drie was hoer as die normale perke. Derhalwe, blyk dit dat verhoogde endo- limfatiese druk weerspieel word in hierdie toetsresultate. Die skrywer is van mening dat impedansmeting-tegnieke in die toekoms, moontlik in die toets- batterei vir diagnose van Meniere se sindroom ingesluit sal word. The difficulties in diagnosing Meniere's disease have been mentioned through- out the literature, b o t h from the point of view of the audiologist and that of the ear, nose and throat specialist. Little research has apparently been con- ducted into the possible application of the recently developed impedance techniques in the diagnosis of this disease. Tydskrif van die Suid-Afrikaans Vereniging vir Spraak- en Gehoorheelkunde, Vol. 22, Deseber 1975 R ep ro du ce d by S ab in et G at ew ay u nd er li ce nc e gr an te d by th e P ub lis he r (d at ed 2 01 2) 50 Linda Lloyd MENIERE'S DISEASE Meniere's disease, an inner ear condition, usually manifests itself as verti- ginous "attacks" with nausea, accompanied by tinnitus and hearing loss. Following the appearance of these symptoms, which may be severe, remission periods occur 2 2 . Prosper Meniere first described this disease in 1861 8 , 3 3 and considered the hearing loss as its cardinal symptom 3 2 . However today, there is confusion in the minds of many, as to the symptoms and pathological changes which should be ascribed to the disease, due mainly to the fluctuation of symptoms. Meniere's disease is thus difficult to diagnose. 7,25,26,32 important factor in diagnosis appears to be that all symptoms vary simultan- eously i.e. they appear to be directly related to one another, 3 2 , 3 3 but even this is in dispute 2 · 2 5 . While some authors consider the symptom triad ne- cessary for diagnosis 6 , 2 6 others do not feel it is necessary 2 7 · 3 2 while yet a third group of authors have added the symptom of 'fullness in the ear' to those mentioned by Meniere. 2 4 , 3 0 Diagnosis is complicated by the fact that while the symptom triad may be present when the disease is fully developed18, any one of the symptoms may preceed the others by months or. years2. The term 'Meniere's disease' has undoubtedly been applied to many other condi- tions, 3 2 a n d the writer feels that new diagnostic procedures should be in- vestigated to assist in diagnosis. It has been hypothesised that the symptoms found in Meniere's disease may be related to increases in edolymphatic pressure. Recruitment and hearing loss are believed to result from hair cell distortion due to pressure increases in the scala media 3 2 . Feldman 3 0 , 2 6 f e e l s that the symptom of fullness in the ear is the subjective impression of saccule dilation, while vertigo occurs when the pressure in the endolymph has built up to its height. The remaining symptom, tinnitus, has not yet been explained8. Originally, endolymphatic hydrops (an accumulation of liquid in the endolymphatic spaces7) was felt to be an essential finding in Meniere's disease 1 0 . This condition was found to have produced dilation of the saccule which occupied the whole vestibule and came into contact with the stapes footplate. Dilation of the scala media was also found. However, some authors have had negative findings in this respect 3 2 . Gen- erally there is agreement that fluctuations in edolymphatic hydrops occur, linked to symptom f l u c t u a t i o n . 1 0 , 3 0 . Many treatments, either medical or surgical, have been developed around the relief of increased endolymphatic pressure 7 , among these are attempts to control the formation and absorption of endolymph 21,31,30 o u e to symptom fluctuations, the success of these treatments is difficult to ascertain 7 , although generally, they have failed to give lasting relief 2 4 . The writer feels that pressure changes within the / endolymph may be detectable in the impedancei characteristics of the middel ear, via the oval window. IMPEDANCE AUDIOMETRY Impedance audiometry was first introduced by Metz, twenty five years ago. It is widely used in Europe and the United States, as an important part of the battery of special audiometric t e s t s 1 4 . The techniques are used and designed to diagnose and distinguish between middle ear pathologies 4 . Determination Journal of the South African Speech and Hearing Association, Vol. 22, December 1975 R ep ro du ce d by S ab in et G at ew ay u nd er li ce nc e gr an te d by th e P ub lis he r (d at ed 2 01 2) Impedance Measurements in Meniere's Disease 51 of the ear canal volume, under various air pressure conditions, is the basis for all measures with the Electroacoustic Impedance Balancing Bridge28. Sensori-neural pathologies, when tested using impedance techniques, appear as normal ears, providing the middle ear is normal. There has thus far been no real distinction between these, using impedance techniques, other than the detection of recruitment in the more severly impaired e a r s 1 2 . Three basic impedance tests are generally used in order to gain a complete pic- ture of the middle ear function:- Tympanometry — "The measurement of eardrum compliance" and mobility "under artificially induced air pressure changes in the ear canal" 1 6 . The mea- surement of the middle ear pressure is included in the test. Acoustic Impedance Measurement - the measurement of the amount of re- sistance to sound waves at the plane of the tympanic membrane5. Acoustic Reflex Measurements — detection of impedance changes as a result of contraction of one or both middle ear muscles5. The absence of this reflex may have several pathological causes9·1 2 while Jerger notes that a small per- centage of normal ears do not exhibit this reflex12. The acoustic reflex is defined as "that level above the threshold of hearing, at which a sound is just capable of eliciting a reflex contraction of the stapedius muscle" 1 6 , this is usually at between 70 - lOOdB SL 1 2 . The reflex test is considered by J e r g e r 1 2 to be the most objective test of recruitment so far constructed. In interpreting the results of these tests, normative data should be known, however this is not yet available excepting in the case of gross middle ear anomalies13. In Metz's study in 1945 wide variation in impedance values were found28 and Jerger reports an overlap between normal and disordered ears 1 2 . There would be great advantages to be gained if impedance techniques could be added to the diagnostic test battery for Meniere's disease to confirm im- pressions already gained by the clinician12. This is especially true in cases of mental retardation or gross physical handicaps where other tests would not be suitable. When considering surgery, which may be unnecessary or dangerous, confirmation of diagnosis is important 2 1 . Variables such as stress, anxiety, fatigue (all exaggerated in sufferers of Meniere's disease), and intell- igence factors could be eliminated due to the nature of impedance t e s t s 8 , 1 6 > 2 4 . These tests have been successfully used in the diagnosis of psychogenic deaf- ness, retro-cochlear pathologies and sensorineural hearing loss with recruit- m e n t 9 , 1 2 · 1 9 · 2 9 which according to Fowler1 6 is a sign of cochlear pathology and therefore to be expected in Meniere's disease. In Subjects with Meniere's disease, Jerger 1 2 found type A tympanograms with normal acoustic impedance. The acoustic reflex was noted to occur at normal intensity levels i.e. 70 - lOOdB but at reduced sensation levels, indica- ting recruitment. However, Zwislocki 3 5 , Feldman 5and Friedman 6 feel that impedance is influenced by the inner ear, notably the compliance of the coch- lear windows and the acoustic impedance at the cochlear entrance 3 5 , which in turn is controlled by conditions existing in the inner ear 3 4 . Pathology of the inner ear that may in turn effect the middle ear via the cochlear windows Tydskrif van die Suid-Afrikanse Vereniging vir Spraak- en Gehoorheelkude, Vol. 22, Desember 1975 R ep ro du ce d by S ab in et G at ew ay u nd er li ce nc e gr an te d by th e P ub lis he r (d at ed 2 01 2) 52 Linda Lloyd may show some anomaly in impedance testing as suggested by Macrae19. According to histological findings, Meniere's disease would qualify as such a disease. METHOD SUBJECTS Ten subjects were obtained by contact with ENT specialists - 6 males be- tween the ages of 27 and 68 years with a mean age of 50 years, and 4 females between the ages of 35 and 62 years with a mean of 48 years 3 months. Due to difficulty in obtaining subjects, it was necessary to include subjects in whom presbycusis could have influenced test results. All subjects were White South Africans from various income groups as noted by their addresses of residence. The subjects were examined by ENT special- ists within 10 months of taking part in the study and a diagnosis of unilateral Meniere's disease was made, based on the symptom triad and case history data. Otoscopic examination, no longer than 4 months prior to the study, con- firmed that no middle ear pathologies existed. Control for the experiment was supplied by the unaffected ear of each subject which was expected to show the normal impedance values for that individual. PROCEDURE Subjects were seen individually and took part in the following: Completion of a questionnaire Pure tone audiometry (air and bone conduction) Impedance audiometry (tympanometry, acoustic impedance test and acoustic reflex measurements) Questionnaire The questionnaire was given to ascertain a possible correlation between the symptoms experienced and the test results. Questions were asked as to which of four symptoms were present, in which ear, with a description of the symp- tom where appropriate. The date of the last attack was also noted. Pure Tone Audiometry Bilateral tests in the ascending order, for air and bone conduction were carried out, using a Maico MA 24 Audiometer, calibrated to the ISO 1964 reference standard and situated in an acoustically treated booth (IAC Series 1604-Act). Bone conduction was carried out for the speech frequencies and narrowband masking was used where appropriate, in air and bone conduction. Impedance Audiometry The Madsen ZO 70 Electro-acoustic Impedance Balancing Bridge was used to obtain the following three measures bilaterally: A tympanogram with readings taken for every pressure change of 50 mm of water. Middle ear pressure was also measured. Acoustic impedance was mea- sured in acoustic ohms and calculated according to the mathematical formula. Journal of the South African Speech and Hearing Association, Vol. 22, December 1975 R ep ro du ce d by S ab in et G at ew ay u nd er li ce nc e gr an te d by th e P ub lis he r (d at ed 2 01 2) Impedance Measurements in Meniere'sDisease 53 Thresholds for the acoustic reflex were obtained for 1000 Hz, 2000 Hz, 4000 Hz, 500 Hz, and 250 Hz in that order, using the ascending method. Auditory signals were provided by an Amplivox 51 audiometer calibrated to the ISO 1964 standard, the limits of the audiometer being as follows:- 250 Hz — 75dB 2000 Hz - 95dB 500 Hz — 85dB 4 0 0 0 H z - 9 5 d B 1000 Hz - 95dB The reflex elicited was recorded for the stimulated ear. RESULTS AND DISCUSSION Q U E S T I O N N A I R E The symptoms included in the questionnaire were Meniere's traid plus 'full- ness in the ear' which is increasingly being thought of as symptomatic of Meniere's disease 7 . 2 4 . 3 o , 3 3 Although each subject had previously exper- ienced all four symptoms, Table I shows that at the time of testing, five felt free of symptoms and five reported symptoms. Of these five subjects, all had tinnitus, four reported hearing losses, one had fullness in the ear and none experienced vertigo. The time that had elapsed since the last attack ranged from 1 to 11 months. SYMPTOMS EXPERIENCED AT THE TIME OF TESTING SUB-SUB- JECTS TINNITUS HEARING LOSS FULLNESS IN THE EAR VERTIGO NONE 1 X X 2 X X -3 X 4 X 5 X 6 X X 7 8 9 X X X X X 10 X TOTAL 5 4 1 0 5 TABLE I. Distribution of Subjects according to number and type of symptoms experienced when tested. Tydskrif van die Suid-Afrikaanse Vereniging vir Spraak- en Gehoorheelkude, Vol. 22, Desember 1975 R ep ro du ce d by S ab in et G at ew ay u nd er li ce nc e gr an te d by th e P ub lis he r (d at ed 2 01 2) 54 Linda Lloyd It could be anticipated that not all symptoms would be experienced by each subject as symptoms are known to fluctuate,2·8 and only the active stage of the disease is characterised by v e r t i g o 2 6 · 3 2 . Of the subjects later found to have hearing losses (seven in all), only four re- ported noticing such a loss. This may be due to compensation for the loss, by the good ear 2 3 · 3 2 for example in the case of Subjects 5 and 7. Tinnitus may also prove so disturbing that the hearing loss goes unnoticed 2 6 . Increased endolymphatic pressure cannot be presumed because of the presence of a hearing loss and/or tinnitus as these are reported to become independent of pressure changes in the later stages of the disease 2 · 2 1 · 3 3 . Only Subject 8 experienced fullness in the ear which Lindsay7 and F i c k 3 0 regard as an indication of increased endolymphatic pressure. It is felt that this Subject could therefore show high acoustic impedance values. In the earlier stages of the disease, Sataloff 2 6 r e p o r t s the occurrence of un- predictable remissions for a few days or years with an unpredictable number of symptoms remaining, although the later stages of the disease are character- ised by the symptom t r i a d 8 · 2 6 . PURE TONE AUDIOMETRY Table II shows that 7 Subjects had hearing losses in the affected ear. Bone conduction thresholds confirmed these losses to be sensori-neural. The only hearing losses seen in the unaffected ears were recorded for Subjects 1 , 5 , 6 , and 8, all over 60 years of age who had falling sensori-neural losses. It is possible that presbycusic hearing losses may have been superimposed on the losses due to Meniere's disease, thus giving the audiograms falling configura- tions wnich may not otherwise have occurred. Sataloff states that with presbycusic losses, both ears will be affected at the same r a t e 2 6 . Three shapes of audiograms were recorded for the effected ears:- Flat - Subject 5 Rising - Subjects 2, 4 and 7 Falling - Subjects 1, 6 and 8 Controversy exists about expected audiometric configurations in Meniere's disease. The report of the Subcommittee on Equilibrium and Its Management25 states that, in the early stages, audiograms may show flat or rising configura- tions. Golding-Wood8 feels that diagnosis may not be made unless the config- uration is falling, as in the later stages of the disease. He also quotes Wright (1942) and Opheim and Flottorp (1957) who found no typical audiogram for Meniere's disease. 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