Fasciculations in motor neuron disease: discharge rate reflects extent and recency of collateral sprouting.

Single fibre EMG recordings were made from 152 fasciculating motor units in 17 patients with motor neuron disease. All recordings showed abnormal jitter, many (75%) displayed intermittent blocking, and most had abnormal fibre density (mean 4.3), demonstrating considerable degrees of collateral sprouting supported by the fasciculating motor units, and varying degrees of functional immaturity of the new axonal twigs and the motor end plates. The SFEMG abnormalities reflecting both the degree and the recency of collateral reinnervation correlated with the mean interdischarge interval, suggesting that the properties of the generator site depend on the functional state of the fasciculating motor unit as a whole.