X-linked recessive bulbospinal neuronopathy (Kennedy's syndrome): a neurophysiological study.

We examined 8 men with X-linked recessive bulbospinal neuronopathy. Quantitative electromyography showed large amplitude motor unit action potentials of prolonged duration and increased polyphasia. There was a pronounced loss of motor units in all but one muscle at maximal volition even in muscles with normal or only mildly decreased force. Denervation activity was present in 53% sampled limb muscles, and fasciculation was recorded in 33% of limb muscles. Nerve conduction studies showed small amplitude sensory action potentials in 6 out of 8 patients. The motor and sensory conduction velocity was normal or borderline slow. The electrophysiologic findings were consistent with chronic partial denervation (motor axonopathy) combined with large fibre sensory axonopathy.