neurophysiological profile of auditory...

Egypt Rheumatol Rehab Vol. 28, No. 4, October 2001

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NEUROPHYSIOLOGICAL PROFILE OF AUDITORY NEUROPATHY

EIMAN M. S. AL-DINASOURY AND MONA MANSOUR HASAB AL-NABY*

Audiology Unit of ENT Department and Rheumatology & Rehabilitation* Department, Ain Shams University Faculty of

Medicine

KEY WORDS: (TEOAES), AUDITORY NEUROPATHY, ABR, NERVE CONDUCTION, SEPS

ABSTRACT Fifteen patients with auditory neuropathy were

investigated for central and/ or peripheral nerve affection. Diagnosis of auditory neuropathy was based on the presence of hearing loss with disproportionate speech discrimination, normal transient otoacoustic emissions (TEOAEs) and absent or abnormal auditory brainstem response (ABR). Neurological examination and electrophysiological testing of the median, ulnar, tibial, peroneal and sural nerves were performed for all patients. Ten normal subjects, matched in age and gender, served as a control group. The results revealed that all patients showed electrophysiological abnormalities either peripheral, central or combined. We conclude that auditory neuropathy is not an isolated disorder but rather part of generalized neuropathy.

INTRODUCTION Auditory neuropathy is a recently described disorder in which

patients demonstrate hearing loss for pure-tones, poor speech discrimination out of proportion to this loss, absent or abnormal auditory brainstem responses and normal outer hair cell function as measured by otoacoustic emissions and cochlear microphonics ( Soliman, 1987; Starr et al., 1991; Doyle et al., 1998 and Deltenre et al., 1999). Few reports denoted that auditory neuropathy is not an extremely pure auditory disorder but it may be a part of a syndrome involving peripheral, vestibular as well as auditory nerves. Cases of auditory neuropathy may be asymptomatic regarding motor

Neurophysiological Profile Of Auditory Neuropathy Dinasoury & Hasab Al-Naby

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or sensory affection (Sheykholeslami et al., 2000) but it may present with severe and progressive motor disability with deafness delayed until the second decade (Butinar et al., 1999). Our study aimed at studying cases of auditory neuropathy for the presence of clinical and or electrophysiological neurological abnormalities in order to identify the features of this clinical disorder in Egyptian patients.

Methodology: Audiological work-up:

Over a period of 18 months, from January 2000 till June 2001, 6235 adult patients were referred to the Audiology unit, Ain Shams University for audiological assessment. Twenty-seven patients were found to have poor speech discrimination disproportionate to the degree and configuration of hearing loss. A diagnosis of auditory neuropathy was achieved in 18 patients. Fifteen of them agreed to be enrolled in the present study.

The battery used for diagnosis included: Pure-tone and speech audiometry using two-channel audiometer Madsen, Model Orbiter 922. Speech material used comprised Arabic spondee (Soliman et al., 1985) and Arabic monosyllabic word tests (Soliman, 1976). Immittancemetry, using acoustic impedancemeter Interacoustics, model AZ7, was done prior to otoacoustic emissions testing to ensure normal middle ear pressure and to detect acoustic reflex thresholds. Transient Evoked Otoacoustic Emissions (TEOAEs) test was performed using non-filtered click stimuli of 80usec. At a rate of 50/sec. and an intensity of 80dBSPL.The test was performed with and without contralateral acoustic stimulation with broadband noise at 70dBSPL. The presence of normal TEOAEs was determined by response amplitude (noise subtracted) of at least 3dB and waveform reproducibility in at least three octave bands of >50%. The presence of normal of normal contralateral suppression was defined by a reduction of TEOAEs of >1dB. Auditory Brainstem Response (ABR) was recorded using Biologic Navigator system. Clicks of 250msec. Duration were presented ipsilaterally at 90dBHL using a repetition rate of 21pulses/sec. Averages were made from 2000 trials using Cz, M1 & M2 electrode montage.

All patients and controls were subjected to full medical history, thorough neurological assessment to exclude any possible known diseases or drug intake that can affect the auditory system, the peripheral or the central nervous system functions. Special inquiry for familial neurological


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disorder was questioned for all patients. Laboratory investigations, in the form of CBC, fasting and post prandial blood sugar, were done.

Nerve conduction studies: Motor conduction studies were done for median, ulnar, peroneal &

tibial nerves. Sensory conduction studies were done for the median, ulnar and sural nerves sides using Evomatic 8000 (Dantic, Denmark) (Dumitru, 1995).

Somatosensory evoked potentials (SEPs): SEPs were done by stimulation of the median and tibial nerves on

both sides using Evomatic 8000 (Dantic, Denmark). The intensity of the stimulus was adjusted to produce visible muscle twitch of the appropriate muscle analysis time for median and tibial nerves were 40 & 80 msec respectively. Electrical stimuli were square pulse wave of 0.2 msec duration delivered at 3 Hz. Potentials were recorded by needle electrodes placed at the somatosensory hand area on the scalp contralateral to the stimulated site (C3\ or C4\). The reference electrode was placed at Fz position for cortical recording electrode. For tibial SEPs recording electrodes were placed at Cz\ and reference electrode at Fz position. Five hundred responses were averaged. Each study was performed at least twice to confirm the reproducibility of the wave forms the absolute latency of the cortical (N19) wave forms were recorded for both median nerves and the absolute latency for the tibial nerve P40 was recorded. Amplitude of evoked responses was recorded base to peak. Amplitude and latency comparisons were made and SEPs were considered abnormal if values were beyond normal values by 2 standard deviations (Dumitru, 1995).

RESULTS The study group consisted of 15 patients fulfilling the criteria of

auditory neuropathy. Their age ranged from 16 to 51years with a mean of 26.7 years + 9.6 Difficulty in understanding speech was the main complaint in 13 patients, while the remaining two patients had a complaint of hearing loss. Duration of the complaint ranged from 2 to 33 years, with a mean of 12.4 years + 8.7. The audiological profile of patients is shown in table (1).

All our patients were neurologically asymptomatic and they had negative family history for neurological disorders. On examination all patients had intact motor and sensory examination except one patient who gave history of frequent falls. On assessment, she had mild form of sensory


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ataxia, positive Rombergism and unsteadiness when standing heel to toe with closed eyes or on tandem walking with mild gait ataxia. This patient had bilateral lost ankle jerks, glove and stocking hypoesthesia with absent vibration sense at the ankles to a 128 Hz tuning fork. Table (1): Audilogical profile of the study group. Auditory abnormality N %

-Mild 4 13.3 -Moderate 15 50 Degree of hearing loss -Severe 11 36.7 -Low frequency HL 26 86.7 Pure tone configuration -Flat frequency HL 4 13.3 -0% 2 6.7 -0 > 20 % 11 36.7 -20 > 40 % 7 23.3 Word discrimination score

-40 % 10 33.3 -Absent 28 93.3 Acoustic reflex -Elevated 2 6.7 -TEOAEs preserved 30 100

Otoacoustic emissions -Absent TEOAEs suppression

30 100

N= number of ears

Neurophysiological results showed abnormal conduction and / or SEPs studies in all patients. The frequency of affection of each of the studied parameters and the level of statistical significance are presented in tables (2 & 3). The affection of peripheral and central pathways was not always combined table (4) shows the distribution of such finding in the nerves examined for both central and peripheral affection.

Figure (1) shows absent right N19 in a male patient 19 years old with intact left N19. This patient had also absent Left tibial evoked potentials. Figure (2) shows tibial SEPs of another patient with delayed latency of P40. This patient had also right delayed latency of median nerve and tibial nerve; bilateral diminished amplitude of M (motor) response of peroneal nerve and absent right sural response.


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Table (2): Distribution of patients according to the frequency of affection of neurophysiological parameters.

Total Bilateral Unilateral Neurophysiological

abnormalities: N (%) N N

Median 4 (26.6 %) 1 3

Ulnar 2 (13.3 %) - 2

Tibial 8 (55.2 %) 3 5 Motor latency prolongation:

peroneal 1 (6.65 %) - 1

Median 1 (6.65 %) 1 -

Ulnar 1 (6.65 %) - 1

Tibial 1 (6.65 %) - 1 Motor amplitude diminution

peroneal 11 (73.3 %) 8 8

Median 0 (0%) 0 0

Ulnar 0 (0%) 0 0

Tibial 4 (26.6%) 2 2

Motor Conduction velocity slowness:

peroneal 3 (20.0 %) 1 2

Median 1 (6.65 %) 1 -

Ulnar 1 (6.65 %) - 1 Sensory latency prolongation:

Tibial 5 (33.3 %) 5 Median (N 19)

6 (40.0 %) 2 4 SEPs Latency prolongation: Tibial

(P40 ) 6 (40.0 %) 4 2

Median (N19 )

11 9 2 SEPs amplitude diminution: Tibial

(P40 ) 1 absent

in 1 -

N = number of patients.


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Table (3): Comparison of neurophysiological parameters between the study and the control groups. Variables Study Control t p Rt median motor latency 4.2 + 0.5 3.1 + 0.3 2.1 < 0.05 Lt median motor latency 4.3 + 0.4 3.2 + 0.3 2.0 < 0.05 Rt tibial amplitude 4.9 + 0.3 8.1 + 3.2 3.7 < 0.01 Lt tibial amplitude 4.9 + 0. 2 8.8 + 2.1 6.7 < 0.001 Rt tibial motor conduction velocity

43.2 + 5.0

57.1 + 7.4 5.8

<0.001

Lt tibial motor conduction velocity

42.9 + 5.1 65.8 + 6.9 6.0 <0.001

Rt peroneal motor amplitude 4.0 + 1.7 6.2 + 1.1 4.3 < 0.001 Lt peroneal motor amplitude 3.2 + 1.7 6.3 + 1.1 5.8 < 0.001 Rt peroneal motor conduction velocity

49.8 + 8.1

63.7 + 8.5 4.7 < 0.001

Lt peroneal motor conduction velocity

48.4 + 8.9 63.9 + 8.4 4.5 < 0.001

Rt SEPs median N19 amplitude 18.8 + 5.6 19.9 + 1.1 3.8 <0.05 NB: only the statistically significant results are displayed. P <0.05: Statistically significant P <0.01: Highly statistically significant p <0.001: Very highlysStatistically significant Table (4): Distribution of the peripheral and central affection of the median and tibial nerves.

Nerves Peripheral affection Central affection Combined Total

Median 8 17 5 30

Tibial 19 9 2 30

Correlation studies were performed between the duration of AN, the

degree of hearing loss, word discrimination scores and different parameters of the neurophysiological test results. Positive correlation was only found between pure-tone thresholds and the median nerve (r= 0.63), ulnar nerve (r= 0.59) and sural nerve (r= 0.56) sensory latencies. Pure-tone thresholds were negatively correlated to SEP tibial amplitude (r= -0.58).


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DISCUSSION All patients with auditory neuropathy examined in this study showed

positive electrophysiological test results in one or more of the examined nerves in spite of the fact that they were clinically asymptomatic regarding neuropathic affection. Our data revealed that nerves of the lower limbs had higher degree of affection compared to those of the upper limbs (table 2 & 3). The pattern encountered was that of mixed sensorimotor polyneuropathy.

The peripheral nerve abnormalities found in our patients were in the form of slowed conductive velocities, increased latency and decreased amplitude. With a neuropathy, and in particular a demyelinating neuropathy, nerve impulses slow when a demyelinated segment of the axon is encountered and then regain normal speed when that segment is passed (Mc Donald, 1980). This type of conduction results in a slowing of nerve conduction velocity. On the other hand, one of the classical signs of axonal neuropathy is a decrease in the amplitude of the whole nerve action potential. Therefore, we can conclude that the type of peripheral nerve affection in our patients is both demyelinating and axonal.

The abnormal SEPs of the median and tibial nerves in the present study indicated a central affection of the pathway. This central affection was either an isolated finding in the nerves examined or combined with peripheral abnormalities (table 4). To the authors’ best knowledge; (Starr et al., 1996) conducted the only available study that examined the possibility of neurophysiological abnormalities in auditory neuropathy. They evaluated the electrodiagnostic evidence of neuropathic affection in seven patients presenting with auditory neuropathy. Cases were evaluated by sural and peroneal nerve conduction studies; five of them were additionally tested for SEPs. Three cases showed absent evoked motor or sensory responses, and only one case had abnormal SEPs. In the present research, none of the tested patients was free from neurophysiological affection. Hence, the use of a wide battery of electrodiagnostic tests was capable of detecting such generalized affection, whether peripheral, central or combined.

A close individual-based inspection of the auditory and neurophysiological data revealed a dual affection at both the peripheral and the central levels. Just as the AN patients are well-known to demonstrate a peripheral and a central auditory deficit (Soliman, 1987 and Starr et al., 1991). They also exhibit the same pattern in the somatosensory system. Stated differently, at least one peripheral abnormality diagnosed by nerve conduction studies, and one central abnormality diagnosed by SEPs test,


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was encountered in every patient in the study group. This implies that auditory neuropathy can be considered as part of a generalized neuropathy rather than being an isolated entity. The significant correlation encountered between pure-tone thresholds and both nerve conduction and SEP studies also implies that a single neuropathalogical basis should be posed to explain the abnormalities in this disorder. The previously suggested hypothesis of auditory dys-synchrony as a cause of AN (Berlin, 1998) seems reasonable to apply on the whole nervous system. This is proved by the intense affection of both ABR and SEP potentials that depend heavily on temporal synchronization. Accordingly, the terminology of neural dys-synchrony would better describe the condition rather than auditory dys-synchrony.

Sensorineural hearing loss have been reported in patients with hereditary and other peripheral neuropathies (Cassandro et al., 1986; Hallpike et al., 1980; Musiek et al., 1982; Raglan et al., 1987; Perez et al., 1988 and Wright & Dyck, 1995). However, the differentiation of the site of hearing loss as cochlear or retrocochlear in origin was hampered by the lack of objective evidence of receptor cochlear function. The work of (Starr et al., 1996) directed the attention to investigate the prevalence of auditory neuropathy in well-documented cases of hereditary motor and sensory peripheral neuropathy (HMSN). Three patients in their AN series had such hereditary disorder.

Butinar et al. (1999) examined three members of a Slovenian Roma (Gypsy) family with hereditary auditory, vestibular, motor and sensory neuropathy. Deafness began in childhood with a severe progressive motor disability and was delayed until the second decade. SEP responses of the median nerve were absent in the three examined cases. They attributed this abnormality to a genetically linked disorder located on chromosome 8q24. Contrary to the above notion, a negative family history of neurological affection in our patients denotes that this form of auditory neuropathy is not necessarily a familial disorder; hence, its etiology should be thoroughly investigated. Whether a genetic cause is incriminated in such disorder or not is subject to future research.


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REFERENCES Berlin CI, Bordelon JSt, John P, Wilensky D, Hurley A, Kluka E and Hood

LJ (1998): Reversing Click Polarity May Uncover Auditory Neuropathy in Infants. Ear and Hearing, 19 (1): 37-47.

Butinar D, Zidar J and Leonardis L (1999): Hereditary, auditory, vestibular, motor, sensory neuropathy in a Slovenian Roma (Gypsy) Kindered. Ann Neurol, 46: 36- 44.

Cassandro E, Mosca F, Sequino L, De Falco FA and Campanella G (2000): Otoneurological findings in Friedreich’s ataxia and other inherited neuropathies. Audiology, 25: 84.

Dumitru D (1995): Electrodiagnostic medicine, Hanley & Belfus, Inc. Philadelphia

Hallpike CS, Harriman DGF, Wells CEC (1980): A case of afferent neuropathy and deafness. J Laryngol Otol 94: 945-64

MacDonald WI (1980): Physiological consequences of demyelination. In: Sumaer AJ, ed. The physiology of peripheral nerve disease. Philadelphia, W.B. Saunders, 265-86.

Musiek FE, Weider DJ and Muller RJ (1982): Audiologic findings in Charcot- Marie- Tooth disease. Acta Otolaryngol, 108: 595- 9.

Perez H, Vilche J, Sevilla T and Martinez L (1988): Audiologic evaluation in Charcot- Marie- Tooth disease. Scand Audiol Suppl, 30: 211-13.

Raglan E, Brasher DK, Trinder E and Rudge P (1987): Auditory function in hereditary motor and sensory neuropathy (Charcot – Marie- Tooth disease). Acta Otolaryngol (Stockh), 103: 50-5.

Sheykholeslami K, Kaga K, Murofushi T and Hughes DW (2000): Vestibular function in auditory neuropathy. Acta Otolaryngol Oct, 120 (7): 849-54

Soliman S (1976): Speech discrimination audiometry using Arabic Phonetically-Balanced words. Ain Shams Medical Journal, 27: 27-30.

Soliman S (1987): Low frequency sensorineural hearing loss: A syndrome. Audiology, 26: 332-338.

Soliman, S, Fathallah, A and Shehata W (1985): Development of the Arabic Staggered Spondaic Words (SSW) test. Proceedings of the 8th Ain Shams Medical Congress, 2: 1220-1246.

Starr A, Mc Pherson D and Patterson J (1991): Absence of both auditory evoked potentials and auditory percepts dependent on timing cues. Brain, 114: 1157-1180.

Starr A, Picton TW, Sininger Y, Hood LJ and Berlin CI (1996): Auditory neuropathy, Brain, 119, 741- 753.


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Wright A and Dyck PJ (1995): Hereditary sensory neuropathy with sensory neuropathy with sensorineural deafness and early onset dementia. Neurology 45: 560-2.

عيالعتالل العصبي السمدراسة آهروفسيولوجية ل النبي حسب منصور منى و صوريالدينا صادق إيمان

جامعة -وحدة السمعيات بقسم األذن و األنف و الحنجرة و قسم الروماتزم و التأهيل، آلية الطب عين شمس

. مريضا يعانون من االعتالل العصبي السمعي15تضمنت الدراسـة

. عصاب طرفيا أو مرآزياصابة األإ تم اجراء اختبارات لهم لبيان مدى يص االعتالل العصبي السمعي بناء على وجود ضعف في تمييز الكلمات غير متوافق مع تشختم

عدم وجود استجابة الختبار جذع المخ أو استجابات مغايرة لدرجة السمع مع وجود أو درجة السمع، . ، أو االثنين معااستجابة طبيعية الختبار االنبعاث الصوتي المثار لألذن

عصاب آلينيكي للجهاز العصبي و دراسة توصيل األلي الفحص اإلإو قد خضعت مجموعة الدراسة وسط و و الشظوي و الربلي و الجهود المثارة للعصبين األيوسط و الزندي و القصبللعصب األ

جراء نفس االختبارات على عشرة أفراد طبيعيين يضاهون مجموعة الدراسة من إ آما تم يالقصب . و الجنسحيث السن

أثبتت نتائج االختبارات العصبية للمرضي تأثر وظيفة العصب سواء طرفيا أو مرآزيا أو بصورة بذاته بل جزء من ا قائمامختلطة و قد أثبتت النتائج أيضا أن االعتالل العصبي السمعي ليس مرض

.عصاباعتالل عام في األ

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