The stapedius reflex tests in retrocochlear hearing disorders.

The commonly used parameters of the stapedius reflex responses in the diagnosis of sensorineural hearing disorders are the reflex threshold level and the persistence of the reflex response on prolonged stimulation, i.e., the reflex decay test. With the object of establishing the sensitivity of these reflex parameters to identify tumours affecting the eighth nerve in the early stages, a series of 97 such cases were examined. The mean hearing loss of the affected ears was 32 dB; 28 of the cases still had normal thresholds of hearing; 95 of the ears demonstrated elevated reflex thresholds and/or pathologic reflex decay. To check the specificity of the test, a control series with sensorineural hearing loss and reflex threshold elevation or pathologic reflex decay was analysed with respect to clinical diagnoses. In every third case of reflex threshold elevation and in every second case of reflex decay, the medical diagnosis confirmed a disease known to be associated with retrocochlear dysfunction. It was also noted that none of the cases with brain stem lesion demonstrated reflex decay--an observation which supports the idea of the reflex decay phenomenon as specifically associated with eighth-nerve lesions.