Classification of autonomic disorders.

Recent advances in our understanding of the pathophysiology of cardiovascular regulation and the metabolism of catecholamines have enabled us to develop an improved system of classification of autonomic disorders. Patients with autonomic impairment, clinically unassociated with other neurological abnormalities, are considered to have the Bradbury-Eggleston syndrome (idiopathic orthostatic hypotension, pure autonomic failure). Individuals whose autonomic failure is accompanied by degeneration in other neurological systems are classified as having the Shy-Drager syndrome (multiple system atrophy with autonomic failure). Patients in whom a deficiency of the enzyme dopamine-beta-hydroxylase is present from birth have many features suggestive of the Bradbury-Eggleston syndrome but manifest normal sweating and biochemically have an elevated plasma and urinary dopamine level. Recognition of these individuals is of particular importance because they are uniquely responsive to treatment with oral dihydroxyphenylserine (L-DOPS). A fourth disorder is baroreflex failure; this disorder is usually due to surgery, trauma, radiation or other injury to the ninth or tenth cranial nerves or the medullary nuclei which their fibers innervate. Patients with baroreflex failure have oscillations between hypertension and hypotension, but these alterations are poorly correlated with posture. Very high levels of plasma norepinephrine are found during the hypertensive phase of baroreflex failure. Baroreflex failure is generally responsive to treatment with clonidine. In conclusion, the diagnosis and therapy of autonomic disorders has improved due to the more precise taxonomy now current.