Otoacoustic emission in myasthenia gravis patients and the role of efferent activation

We performed transient evoked otoacoustic emission (TEOAE) measurements on 29 ears of myasthenia gravis (MG) patients. The purpose of the study was to support the role of acetylcholine (ACh) in the efferent innervation of coc hlear outer hair cells (OHCs). Another aim was to establish additional diag nostic tools for the early determination of MG. Initially, threshold audiom etry and impedance measurements showed normal values on the ears examined. The main finding was that TEOAE values were significantly lower in MG patie nts than in healthy controls. Mestinon, a reversible cholinesterase inhibit or, resulted in a significant increase in mean values of TEOAEs, although t hese values were still lower than normal. The results suggest that in MG, a cetylcholine receptor (AChR) autoantibodies inhibit the function of OHC ACh Rs. Thus, the TEOAE generated by the active movements of OHCs is decreased in MG. Mestinon prevents the degradation of ACh, and thus stimulates effere nt function and increases TEOAE values. The results obtained in this study support the role of ACh in the efferent function of OHC, as well as the imp aired function of hair cell AChRs in MG patients. Consequently, measuring T EOAEs may be useful in the early diagnosis of some forms of MG. These resul ts reinforce the importance of collaboration between neurologists and otola ryngologists in the management of diseases with pathological neurotransmiss ion. (C) 1998 Elsevier Science B.V. All rights reserved.