The relaxation time of the stapedius reflex in dystrophia myotonica (Steinert)

Eight patients with dystrophia myotonica (Steinert) were studied. They all had myotonia and pathological EMG and in some cases other signs of the disease. The 50% relaxation times of the stapedius reflex were significantly prolonged compared with a control group of 40 healthy, young subjects with normal hearing and normal stapedius reflex thresholds. The relaxation times could be well quantified and had a low standard deviation from the mean in the control group. In the patient group as well as in the control group only slight differences in the relaxation times were found between the frequencies 500 and 2000 Hz and between the simultaneously measured ipsilateral and contralateral reflexes. It was concluded that measurement of the relaxation time of the stapedius reflex increases the diagnostic possibilities in patients with myotonia.