Neurophysiologic evaluation of lower motor neuron damage in tetraplegia.

We quantitatively investigated the extent of damage to motor neurons in tetraplegic subjects. Numbers of motor units in the patients were significantly lower for thenar, wrist extensor, and biceps brachii as compared to controls. Reduction in counts occurred even when M-response amplitudes were normal. Standard electromyography suggested a surprising frequency of lower motor neuron dysfunction below the level of injury. These results confirm previous reports and add data on motor units in the biceps brachii.