Syndromes of autonomic insufficiency associated with orthostatic intolerance: classification, diagnostic and therapeutic approach

Stimulated by the widespread use of tilt table testing, disorders of autono mic function with orthostatic hypotension have recently gained attention by clinical cardiologists. At the same time, improved characterization of the underlying circulatory responses have led to a reclassification of these s yndromes. In particular, three subgroups of chronic primary dysautonomia ha ve been defined such as Pure Autonomic Dysfunction, Multiple System Atrophy , and the Postural Orthostatic Tachycardia Syndrome. On the other hand, acu te dysautonomias represent a rare yet clinically sometimes dramatic form of autonomic disorders. Several diseases as well as enzymatic disorders, and pharmacological drugs may cause secondary dysautonomia. The clinical correl ate of all these forms of dysautonomia is orthostatic hypotension and synco pe. Thus, a careful history forms the basis of a successful diagnostic work up of the underlying cause of syncope. This review summarizes the current k nowledge of autonomic disorders, their classification and diagnostic and th erapeutic strategies.