[Relation between the clinical manifestations and electromyographic findings in motor neurone disease]

343 cases of motor neurone disease (MND) were examined with electromyography. The result showed EMG examination was of much vale in helping to ascertain an accurate diagnosis which clinically could be made in only about 1/4 of the series of cases. The ages of onset ranged from 4 months to 10 years with an average of 36.8 years. 56.8% under 40 years. There was a higher male preponderance, the male/female ratio being 3.2:1. It was 1.6:1 in a report from a western country. 123 cases showed only one limb involvement clinically while the EMG findings were also abnormal in the other three limbs. Fibrillation potentials were found to be at more than two sites in one muscle in 84.5% in this series, where as they occurred in 95-100% of the infantile and juvenile cases. Abundant fibrillation potentials were found in 37.1% of the cases within 3 years after the onset and in 13.6% in those with a longer duration. The increment of the mean duration of motor unit potential was 94.5% and that of the mean amplitude 91%. It seemed not necessary to emphasize giant potentials. The motor nerve conduction velocities (NCV) were normal in 95% while the sensory NCV were almost always normal (98%). All of the 3 cases tested with single fiber EMG showed an increment of jitter of 95-100% and a muscle fiber density of 2.95-3.65.