蝸電図よりみた突発性難聴の病態

ELECTRO-COCHLEOGRAPHIC STUDY OF SUDDEN DEAFNESS

　I．緒言

　突発性難聴は厚生省特定疾患に指定され，疫学，病因および治療面にわたり種々検討され，またメニエール病との類似点，相違点に関してもメニエール病調査研究班との合同会議において多くの研究報告がなされている。

　すでにわれわれは突発性難聴に蝸電図検査を行ない，蝸電図法により突発性難聴の予後を早期に判定し得ることを報告した^1）。今回は突発性難聴症例から得られた蝸電図の聴神経活動電位（AP），蝸牛マイクロフォン電位（CM），Summating Potential（SP）の各種反応から本疾患の病態について検討したので報告する。

　Pathophysiology of the sudden deafness is studied by means of electrocochleography. The patterns of the wave-forms of electrocochleograms (AP, SP) obtained from 34 cases of sudden deafness were divided into the following types: 1. AP high response; 2. decreased AP high response; 3. AP low response; 4. Dominant -SP; 5. +SP or -SP; 6. AP, SP no response. Satisfactory prognosis was seen in cases that showed dominant -SP and high response AP.

　In these cases the sensory epithelium and the cochlear nerve which appeared to have been affected by temporary functional block showed a reversible condition. On the other hand, it appeared that the neural region related to the source of AP, N₁ response were impaired in cases in which CM were recorded at normal response threshold in spite of the absence of AP N₁ response. Furthermore, in cases of unsatisfactory prognosis the following types appeared to be outstanding, i.e. with decreased AP high response, those with AP low response and AP, SP no response in which CM response had also disappeared. In these cases it seemed that the sensory epithelium and the cochlear nerve were affected organically although the degree of impairment may be varied.

　In cases of Ménière's disease, the types showing AP high response and dominant -SP with normal response threshold of CM was also recorded. But, hearing acuity was scarcely recovered among these cases.

　Upon the basis of these observations, the authors conclude, that the difference between the loss of hearing in Ménière's disease and that of the sudden deafness having satisfactory prognosis may be traced to the difference between the physical and chemical alteration of the endolymphatic space such as endolymphatic hydrops in the former and a temporary alteration of the neurosensory structure in the latter.