STIMULATION FREQUENCY-DEPENDENT NEUROMUSCULAR-JUNCTION TRANSMISSION DEFECTS IN PATIENTS WITH PRIOR POLIOMYELITIS

Generalized fatigue and muscle fatiguability are major symptoms of pos t-poliomyelitis syndrome (PPS), and may be due to neuromuscular juncti on transmission defects, as suggested by increased jitter on single fi ber electromyography (SFEMG). To determine the etiology of this defect , we studied jitter at low (1, 5 Hz) and high (10, 15, 20 Hz) frequenc y stimulation with stimulation SFEMG in 17 post-polio patients with mu scle fatiguability, and in 9 normal controls. In 5 of 17 PPS patients and in 1 of 9 controls, jitter was significantly higher (unpaired t-te st, P < 0.05) at high frequency stimulation (HFS). In the remaining PP S patients and controls there was no significant difference in jitter at high and low stimulation frequencies. PPS patients with increased j itter at HFS had a significantly longer time interval since acute poli o (mean 48.5 years) than PPS patients without increased jitter at HFS (mean 40 years; P < 0.05), but were not distinguished by other histori cal or clinical criteria. We conclude that the neuromuscular junction defect in post-polio patients is similar to that observed in amyotroph ic lateral sclerosis, and is probably due to ineffective conduction al ong immature nerve sprouts and exhaustion of acetylcholine stores. The appearance of an increase in jitter with HFS in post-polio patients m ay be dependent upon time after acute polio.