A progressive neurodegenerative condition of the central and autonomic nervous systems characterized by atrophy of the preganglionic lateral horn neurons of the thoracic spinal cord, which differentiates this condition from other forms of idiopathic orthostatic hypotension (HYPOTENSION, ORTHOSTATIC). This disease is generally considered a clinical variant of MULTIPLE SYSTEM ATROPHY. Affected individuals present in the fifth or sixth decade with orthostasis and bladder dysfunction; and later develop FECAL INCONTINENCE; anhidrosis; ATAXIA; IMPOTENCE; and alterations of tone suggestive of basal ganglia dysfunction. (From Adams et al., Principles of Neurology, 6th ed, p536).