An acquired form of orthostatic intolerance, referred to as sympathotonic orthostatic hypotension (Polinsky et al), may represent another variant or partial form of autonomic paralysis. In this syndrome, unlike the common forms of orthostatic hypotension (see later), the fall in blood pressure is accompanied by tachycardia. Hoeldtke and colleagues, who described 4 such patients, found that the vasomotor reflexes and NE production were normal; these investigators were inclined to attribute the disorder to a process affecting lower thoracic and lumbar sympathetic neurons. Its relationship to the entity of postural orthostatic tachycardia syndrome (POTS) discussed in Chap. 17 and to the orthostatic intolerance associated with the chronic fatigue syndrome is uncertain. Individual cases of POTS have been associated with mutations or epigenetic alterations in the norepinephrine transporter gene (Shannon and colleagues, 2005). Some instances of orthostatic intolerance appear as part of the asthenia–anxiety disorders in which the autonomic changes may represent sympathetic overactivity in susceptible individuals.
There are several reports of improvement of pandysautonomia after intravenous gamma globulin infusion, but these are difficult to judge as many patients improve spontaneously over the same time frame, usually many months. In addition, plasma exchange has been used with apparent benefit in a patient with antibodies against the ganglionic acetylcholine receptor (Schroeder et al).
As more experience accumulated over years, it became apparent that acute autonomic neuropathies represent a spectrum of disorders and majority are likely immune-mediated. These disorders include acute autoimmune ganglionopathy—idiopathic or paraneoplastic, (previously called panautonomic neuropathy or pandysautonomia) characterized by severe and widespread sympathetic and parasympathetic failure. Other forms of acute autonomic neuropathies are acute cholinergic neuropathy, Guillain-Barré syndrome, botulism, porphyria, drug-induced or toxic. Restricted forms of acute autonomic neuropathies may results in postural tachycardia syndrome or motility disorders. Some patients with acute autonomic neuropathies have autoantibodies to the A3 acetylcholine receptor. Somatic involvement of variable severity is seen in majority of acute autonomic neuropathies.
Lambert-Eaton myasthenic syndrome One of the characteristic features of the fully developed Lambert-Eaton myasthenic syndrome, which is discussed in Chap. 46, is dysautonomia, characterized by dryness of the mouth, erectile dysfunction, difficulty in starting the urinary stream, and constipation. Presumably, circulating antibodies against the voltage-gated calcium channel interfere with the release of ACh at both muscarinic and nicotinic sites.
Multiple System Atrophy and Pure Autonomic Failure (See Also Chaps. 17 and 38)