Sympathetic skin response in monomelic amyotrophy

Objectives-Monomelic amyotrophy (MMA) a variant of motor neuron disease, ha s the characteristic features of wasting and weakness usually confined to a single upper or lower limb occurring predominantly in young males and a be nign outcome. Symptoms of increased sweating, coldness and cyanosis have be en observed in a few patients. The objective was to evaluate the involvemen t of the sympathetic nervous system in MMA by measuring sympathetic skin re sponse. Methods Electromyography, motor and sensory nerve conduction studie s were done in all the four limbs of 9 patients with atrophy of one upper l imb. Stimulation at Erb's point, and above and below elbow was done to look for evidence of conduction block. The sympathetic skin response (SSR) was recorded in all the limbs of these patients. Wasting and weakness of right upper limb in 7 patients and left upper limb in 2 patients was seen. The me an age was 28.3 +/- 10.1 years. Twenty-five age matched (24.8 +/-4.8 years) healthy subjects served as controls. Results-The mean SSR latency in the a ffected upper limbs of 9 patients was prolonged compared to the 25 control subjects (1.51 +/-0.07 s vs 1.42 +/-0.19 s, P=0.03). The mean value of SSR latency in 18 upper limbs of the 9 patients which included atrophied and un atrophied limbs was also prolonged compared to the controls (1.50 +/-0.08 s vs 1.42 +/-0.19 s, P=0.05). There was no significant difference of the mea n latency of SSR between the atrophied upper limbs and the clinically norma l upper limbs (1.51 +/-0.07 s vs 1.49 +/-0.09 s, P=0.51). The mean SSR late ncy in the lower limbs of the patients (2.09 +/-0.09 s) did not significant ly differ from the control subjects (1.97 +/-0.28 s, P=0.09). Motor and sen sory nerve conduction was normal and there was no evidence of conduction bl ock. Conclusion In MMA the sympathetic nervous system is involved in the at rophic upper limb and also in the clinically unaffected upper limb but not in the lower limbs.