Comparison of electrophysiological manifestations in Kennedy's disease and progressive muscular atrophy

Abstract

Objective To assess the utility of electrophysiological studies in differential diagnosis of Kennedy's disease(KD)and progressive muscular atrophy(PMA).Methods Thirteen patients with KD and 12 patients with PMA were recruited.The characteristic of onset and duration of disease,motor nerve conduction studies,sensory nerve conduction studies,electromyography and single fiber electromyography were compared between KD and PMA.Results Eleven patients with KD and 1 patient with PMA presented weakness in both lower limbs at onset.The mean compound muscle action potential(CMAP)amplitude ratio of abductor pollicis brevis/abductor digiti minimi in the same side were 1.11±0.40 in KD and 0.57±0.29in PMA(t=4.760,P=0.000).Decreased amplitude of sensory nerve action potential was detected in 6 patients with KD,with bilateral median and ulnar nerve involved in 3 patients,unilateral ulnar nerve involved in 1 patient,bilateral median,ulnar,tibial and peroneal nerve involved in 2 patients.The sensory nerve conduction studies were normal in all patients with PMA.Single fiber electromyography showed that mean jitter was(56.3±24.2)μs in KD and(97.1±35.3)μs in PMA(t=2.696,P=0.015),M_(50) of the percentage of block wag 0 in KD and 32.5% in PMA(Z=3.168,P=0.002).All patients with KD and PMA had extensive neumgenic changes in electromyography study.Conclusions When patient presents symmetric proximal weakness in bilateral lower limbs at onset,nerve conduction studies show CMAP amplitude ratio of abductor pollicis brevis/abductor digiti minimi in the same side is more than 1,and decreased amplitude of sensory nerve action potential with normal conduction velocity.single fiber electromyography shows normal or mild increased mean jitter,the diagnosis of KD but not PMA should be considered. Key words: Muscular atrophy,spinal; Electromyography; Neural conduction; Diagnosis,differential