Selective vulnerability of urinary Onuf motoneurons in Shy-Drager syndrome.

Electrophysiological investigations in a patient with progressive autonomic failure revealed selective damage to the somatic efferent innervation of the external urinary sphincter musculature, implying selective vulnerability of the motoneurons of Onuf's nucleus in the sacral cord. This vulnerability contrasts with the selective resistance of these motoneurons to degeneration in motor neuron disease.