Evaluating dysfunction of the autonomic nervous system.

Simple bedside measurements of blood pressure and systolic pressure response to the Valsalva maneuver will confirm a clinical impression of orthostatic hypotension. Careful questioning of the patient usually elicits other symptoms of autonomic nervous system dysfunction, such as impotence, urinary and fecal incontinence, constipation or diarrhea, blurred vision, or sweating changes. Drugs are the most common cause of autonomic dysfunction, and their benefits should be weighed against the severity of the dysfunction. In addition, diabetes mellitus, uremia, amyloidosis, acute intermittent porphyria, myeloma, tabes dorsalis, and alcohol-nutritional problems may produce symptoms of autonomic dysfunction. Thus, patients who present with autonomic features but no history of dysfunction-producing drugs should undergo complete laboratory evaluation. A regimen of tyramine or L-dopa or a diet rich in cheese, processed meats, and wine (a monoamine), coupled with a monoamine oxidase inhibitor have beneficial effects in patients with orthostatic hypotension due to preganglionic autonomic dysfunction. Patients who do not respond to catecholamine precursors have stable, isolated orthostatic hypotension or a polyneuropathy such as that caused by diabetes.