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Irreversible cochlear damage in myasthenia gravis -- otoacoustic emission analysis
S A Hamed1, A M Elattar, E A Hamed
1Department of Neurology, Assiut University Hospital, Assiut, Egypt. hamed_sherifa@yahoo.com
Objective:
Acetyl choline (ACh) is the main neurotransmitter of the efferent auditory system. This study is aimed to evaluate cochlear function in myasthenia gravis (MG), a neuromuscular transmission disorder caused by ACh receptor autoantibodies.
Methods:
This prospective study included 16 myasthenic patients, tested audiologically twice, first after improvement from myasthenic crisis or acute oropharyngeal dysfunction (1 week from admission) and then 2 months later. We detected the effect of contralateral acoustic stimulation (CAS) on patients' transient and distortion product otoacoustic emissions (TEOAE and DPOAE).
Results:
Compared with controls, patients reported significant reduction in overall echo response and amplitude of TEOAEs at 1-2 kHz and at 1-6 kHz of DPOAE with marked reduction at 5 kHz. In the control group, CAS produced amplitude reduction in TEOAEs and DPOAEs at 1-4 kHz. Utilizing masking effect, patients reported amplitude reduction in TEOAEs at 1.5-4 kHz while DPOAEs did not reach significant level except at 1.5 and 5 kHz. After 2 months, no changes were observed compared with early assessment.
Conclusions:
It is clear that disease progression is associated with irreversible cochlear damage. Lack of improvement in patients' emissions despite partial non-audiometric improvement in relation to receptors needs to be considered.
