Clinical Presentation of Autonomic Disorders

Autonomic disorders may be classified as peripheral or central and acute or chronic disorders.

ACUTE PERIPHERAL AUTONOMIC DISORDERS

Acute/subacute autonomic neuropathies are usually due to toxic, metabolic, autoimmune, or paraneoplastic causes. Primary autonomic polyneuropathies represent an uncommon subgroup. However, many length-dependent polyneuropathies have associated autonomic fiber involvement. Impotence is such an example in diabetic polyneuropathies.

Antecedent viral infections may occur in patients with autoimmune autonomic neuropathy, suggesting that it may be a variant of Guillain-Barré syndrome. They usually have severe generalized disorders, but restricted milder forms also occur. Orthostatic intolerance and gastrointestinal dysmotility are common presentations. Autonomic tests are abnormal. Recovery is slow and incomplete. High titers of ganglionic nicotinic acetylcholine receptor antibodies are reported, supporting an autoimmune basis.

Guillain-Barré syndrome preferentially involves somatic fibers but causes dysautonomia in two thirds of cases, especially affecting the cardiovascular and gastrointestinal systems. Bladder dysfunction is less common. Autonomic complications may be life-threatening; patients must be monitored in the intensive care unit.

Paraneoplastic autonomic neuropathy is indistinguishable from autoimmune autonomic neuropathy. Gastrointestinal dysmotility is a common manifestation. Antineuronal nuclear antibody type 1 is associated with small cell lung cancer. In the Lambert-Eaton myasthenic syndrome, which is associated with presynaptic voltage-gated calcium channel antibody (P/Q type), significant dysautonomia may occur.

Hereditary porphyria manifests with acute attacks of dysautonomic symptoms (abdominal pain, vomiting, constipation, hypertension, and tachycardia) in addition to motor polyneuropathies. Diagnosis requires demonstration of increased urinary excretion of porphobilinogen.

Toxins, including medications (particularly cisplatinum and vinca alkaloids) may cause peripheral neuropathies with autonomic features. Other autonomic nerve toxins include organophosphates, thallium, arsenic, hexacarbons, and acrylamide.

CHRONIC PERIPHERAL AUTONOMIC DISORDERS

Autonomic neuropathies are common accompaniments of diabetic peripheral neuropathies and correlate with duration and control of diabetes. Autonomic testing reveals evidence of cardiovagal dysfunction manifested by impairment of heart rate response to Valsalva maneuver or to deep breathing.

Postural orthostatic tachycardia syndrome (POTS) is seen predominantly in young women. It is characterized by orthostatic symptoms associated with significant rise in heart rate on standing, without orthostatic hypotension or other clinical or laboratory evidence of autonomic neuropathy, except for distal loss of sweating.

Amyloidosis is a multisystem disorder that may be sporadic or familial. Autonomic neuropathy often occurs and presents with symptoms of somatic small fiber dysfunction, orthostatic intolerance, and constipation alternating with diarrhea.

Pure autonomic failure is also known as idiopathic orthostatic hypotension. It is an insidious process with typical signs of disordered autonomic function. The absence of parkinsonian features helps differentiate this disorder from multiple systems atrophy. It results from postganglionic sympathetic neuron degeneration.

Hereditary autonomic neuropathies are rare disorders. Hereditary sensory and autonomic neuropathy type III, also known as Riley-Day syndrome, is an autosomal recessive disorder with defective control of blood pressure, sweating, temperature, and lacrimation in children. Dysautonomic manifestations are less pronounced in other hereditary sensory and autonomic neuropathies.

CENTRAL DISORDERS

Parkinson disease is associated with significant autonomic dysfunction, particularly in long-standing disease. There is loss of pigmented dopaminergic cells in substantia nigra; other pigmented nuclei, including locus ceruleus and dorsal vagal nucleus are affected; this may explain the dysautonomia. Peripheral sympathetic denervation of the heart is common, resulting in orthostatic hypotension in severe cases.

Multiple systems atrophy, a degenerative disorder, is characterized by parkinsonian features with autonomic, cerebellar, and corticospinal involvement. When autonomic symptoms predominate, the disorder is called Shy-Drager syndrome.

Spinal cord disorders may also cause autonomic symptoms. Common disorders include trauma, syringomyelia, and multiple sclerosis. They usually manifest with arrhythmias, blood pressure lability, and bladder atony.

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