Motor unit potentials in a mildly affected muscle in amyotrophic lateral sclerosis

Quantitative analysis of motor unit potentials (MUPs) with spike triggering and averaging was performed from the mildly affected brachial biceps muscle of 18 patients with amyotrophic lateral sclerosis (ALS) and of 18 age-matched controls. The total MUP duration was only 6% higher in ALS patients than in controls (P less than 0.05) while the durations of the main MUP and fast components were prolonged by 63% and 194% (P less than 0.001), respectively. The number of satellites, number of fast components and amplitude were also significantly increased in the ALS group. It is concluded that determination of the duration and number of fast components and the MUP amplitude will sensitively pick up mild neurogenic affection of the brachial biceps muscle.