KIMURA, I., AYYAR, D.R., SATO, G. and KOGURE, K.
Electromyographic Assessment of Fatiguability and Recovery of Orbicularis Oculi in Myasthenia Gravis. Tohoku J. exp. Med., 1983,
141 (3), 351-358 - Orbicularis oculi fatiguability following maximal voluntary contraction and its recovery after administration of Tensilon (edrophonium chloride) were studied in 13 patients with myasthenia gravis (MG) and 8 normal controls. The number of EMG pulses per sec (
C) was calculated using an experimentally manufactured EMG pulse counting system and the mean amplitude of the motor unit potentials per sec (
A) was measured using the action potential analysis module (Medelec APA-6 MK-1) during maximal voluntary contraction of the orbicularis oculi muscle. Fatiguability was estimated as percentage change of
C, the pre-exercise value being taken as 100%. It was 74.4±18.2% (mean±S.D.) in patients and was significantly different from 110.8±8.4% found in the controls (
p<0.01). Recovery following intravenous injection of Tensilon was estimated as percentage change in
C and
A, the values before Tensilon injection being taken as 100%. The change in EMG pulse per sec (
C) was 360.0±90.0% in MG and 113.0+21.2% in controls (
p<0.005). The mean amplitude of the motor unit potential per sec (
A) increased by 180.0±95.0% in MG and 120.0±42.0% in controls (
p<0.01). This technique is thought to be valuable to confirm the diagnosis of MG when routine electrophysiological tests fail to demonstrate abnormalities in neuromuscular transmission.
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