Conduction velocity and refractory period of single motor nerve fibres in motor neuron disease.

Electromyographic single motor unit recordings were used to study the axonal conduction velocity and the axonal refractory period of 60 motor units in patients with severe motor neuron disease. Eighteen per cent of the motor units had abnormally low axonal conduction velocity probably due to secondary degenerative changes. Thirty-two per cent of the motor units had abnormally long axonal refractory period but normal conduction velocity. Whether this reflects a primary disease mechanism or secondary changes remains to be established.