DISORDERS OF THE AUTONOMIC NERVOUS SYSTEM
Autonomic disorders may occur with many disorders of the central and/or peripheral nervous systems (Table 189-2). Diseases of the CNS may cause ANS dysfunction at many levels, including hypothalamus, brainstem, or spinal cord.
|I. Autonomic Disorders with Brain Involvement|
|II. Autonomic Disorders with Spinal Cord Involvement|
|III. Autonomic Neuropathies|
Multiple system atrophy (MSA) is a progressive neurodegenerative disorder comprising autonomic failure (OH and/or a neurogenic bladder) combined with either parkinsonism (MSA-p) or cerebellar signs (MSA-c), often with progressive cognitive dysfunction. Dysautonomia is also common in advanced Parkinson’s disease and in dementia with Lewy bodies.
Spinal cord injury may produce autonomic hyperreflexia affecting bowel, bladder, sexual, temperature-regulation, or cardiovascular functions. With spinal cord lesions above T6, increased autonomic discharges (autonomic dysreflexia) can be elicited by irritation of bladder, skin, or muscles. Bladder distention from palpation, catheter insertion, catheter obstruction, or urinary infection is a common and correctable trigger of autonomic dysreflexia. Dangerous increases or decreases in body temperature can result from an inability to experience the sensory accompaniments of heat or cold exposure below the level of injury.
Peripheral neuropathies affecting small myelinated and unmyelinated fibers of the sympathetic and parasympathetic nerves are the most common cause of chronic autonomic insufficiency (Chap. 196: Peripheral Neuropathies, Including Guillain-Barré Syndrome). Autonomic involvement in diabetes mellitus typically begins ∼10 years after onset of diabetes and slowly progresses. Diabetic enteric neuropathy produces gastroparesis, nausea and vomiting, malnutrition, achlorhydria, and bowel incontinence. Impotence, urinary incontinence, pupillary abnormalities, and OH may occur as well. Prolongation of the QT interval increases risk of sudden death. Autonomic neuropathy occurs in sporadic and familial forms of amyloidosis. Pts typically present with distal, painful polyneuropathy. Alcoholic polyneuropathy produces symptoms of autonomic failure when the neuropathy is severe, and autonomic involvement contributes to the high mortality rates associated with alcoholism. Attacks of acute intermittent porphyria (AIP) are associated with tachycardia, sweating, urinary retention, and hypertension; other prominent symptoms include anxiety, abdominal pain, nausea, and vomiting. BP fluctuation and cardiac arrhythmias can be severe in Guillain-Barré syndrome. Autoimmune autonomic ganglionopathy presents as the subacute development of autonomic failure with OH, enteric neuropathy (gastroparesis, ileus, constipation/diarrhea), flaccid bladder, loss of sweating, sicca complex, and a tonic pupil. Onset may follow a viral infection; serum antibodies to the α3 subunit of the ganglionic ACh receptor (α3AChR) are diagnostic, and some pts appear to respond to immunotherapy. Rare pts develop dysautonomia as a paraneoplastic disorder (Chap. 79: Neurologic Paraneoplastic Syndromes). There are five known hereditary sensory and autonomic neuropathies (HSAN I–V).
Botulism is associated with blurred vision, dry mouth, nausea, unreactive or sluggishly reactive pupils, urinary retention, and constipation. Postural orthostatic tachycardia syndrome (POTS) presents with symptoms of orthostatic intolerance (not OH), including shortness of breath, light-headedness, and exercise intolerance accompanied by an increase in heart rate but no drop in bp. Primary hyperhidrosis affects 0.6–1.0% of the population; the usual symptoms are excessive sweating of the palms and soles. Onset is in adolescence, and symptoms tend to improve with age. Although not dangerous, this condition is socially embarrassing; treatment with sympathectomy or local injection of botulinum toxin is often effective.
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