Decay and recovery of the stapedial reflex by prolonged stimulation in the diagnosis of myasthenia gravis.

The decay and recovery of stapedial reflex amplitude was investigated in 19 patients with myasthenia gravis and 30 control subjects. In 9 untreated patients the amplitude was reduced to less than 10% of the initial amplitude following continuous stimulation for 120 s, whereas the maximum decay in the control subjects was only 50%. In the group of treated patients the reflex decay showed individual variations. The rate of recovery after prolonged stimulation (5 min) was slower in the patient group, especially within the first 30 s of recovery. With increasing age, the rate of decay rose in the patient group as well as in the control group. The technical parameters necessary for obtaining information of clear diagnostic value are indicated, with which it was shown that the continuous prolonged stimulation of the stapedial muscle is a practical and valid method for the evaluation of patients with myasthenia gravis.