Autonomic neuropathies.

There is a spectrum of acute autonomic neuropathies. Acute panautonomic neuropathy (pandysautonomia), characterized by severe widespread sympathetic and parasympathetic failure, is at one extreme. Guillain-Barré syndrome is at the other end of the spectrum, where the brunt of the disorder falls on the somatic nervous system. Pure acute panautonomic neuropathies are relatively rare. The majority of acute autonomic neuropathies have some minor somatic features. Dysautonomia may be restricted to the cholinergic system (acute cholinergic neuropathy), adrenergic system, or other organ systems (eg, motility disorders). Recently, an important gap in the clinical description of idiopathic autonomic neuropathies and their course was filled, with neurologic and autonomic testing end-points. About one in four to one in three patients will improve substantially. Two other manifestations of autonomic neuropathy are the pseudoobstruction and postural tachycardia syndromes. Loss of the baroreceptors and consequent impairment of buffering of blood pressure results in wild swings in blood pressure that are treatable. Correcting anemia improves orthostatic tolerance, if necessary by hemopoietin. Improved evaluation of neural structure, in skin and in the laboratory, has led to better quantitation of autonomic failure and mechanisms of syncope. This understanding has been extended to the frequency domain and to a study of cerebral vasoregulation.