Irreversible cochlear damage in myasthenia gravis - otoacoustic emission analysis

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.