The Most Common Causes of Autonomic Nervous System Dysfunction

Dysautonomia and Trouble with The Autonomic Nervous System

Nervous System
Nervous System. Handout / Handout / Getty Images

The autonomic nervous system controls important bodily functions like heart rate and blood pressure that keep us alive without our ever thinking of them. Almost any medical disorder can affect the autonomic nervous system in some way, though relatively few diseases attack the autonomic nervous system alone. Below are some of the most common forms of autonomic nervous system dysfunction, or dysautonomia:

Acute Autonomic Paralysis

Acute autonomic paralysis, first described in 1975, remains extremely rare but serves as a good example of what happens when all autonomic nervous functions are compromised. Symptoms come on over a week or a few weeks with complete loss of most autonomic functions and include dry eyes, orthostatic hypotension, lack of salivation, impotence, impaired bladder and bowel function, and abdominal pain and vomiting. Both parasympathetic and sympathetic fibers are impacted, though other nerves are spared. A lumbar puncture may demonstrate elevated protein in the CSF. The cause is rarely found, though it's likely an autoimmune disease similar to Guillain-Barre syndrome. The best treatment is unclear, though some have suggested improvement after plasma exchange, or IVIG administration.

Idiopathic Orthostatic Hypotension

A rare degenerative disease, idiopathic orthostatic hypotension comes on in mid to late life and involves lesions in the post-ganglionic sympathetic neurons, which prevent the heart from speeding up when needed.

This is very rare; a more common central preganglionic dysautonomia involves degeneration of part of the spinal cord through which autonomic nerve fibers travel in the lateral horn. In either case, treatment starts with noninvasive lifestyle changes, including wearing pressure stockings, and slowly transitioning from sitting to standing.

If this is insufficient, medications such as midrodine or florinef may be necessary.

Secondary Orthostatic Hypotension

In this very prevalent form of dysautonomia, a peripheral neuropathy, such as that found in diabetes, also impacts the peripheral autonomic nervous system. There is a wide variety of other causes, including heavy alcohol use, nutritional deficiencies, or toxic exposures.

The dysautonomia accompanying diabetic neuropathy is particularly common and may present with impotence, diarrhea, and constipation, in addition to orthostatic hypotension. These symptoms may or may not be as severe as the accompanying sensory changes caused by the diabetic peripheral neuropathy. It's also important to note that these peripheral neuropathies sometimes pre-date the diagnosis of diabetes, and some laboratory tests used to diagnose diabetes, such as the hemoglobin A1c level, may still be within normal range. In other words, the peripheral nerves can be more sensitive than the diagnostic tests used by physicians to detect diabetes.

Other forms of peripheral neuropathy, such as that caused by amyloidosis, have even stronger dysautonomias. The inherited neuropathy caused by Fabry disease (alpha galactosidase deficiency) can also cause a pronounced dysautonomia.

Riley-Day Syndrome

While about a quarter of people over the age of 65 have some kind of dysautonomia as indicated by orhtostatic hypotension, dysautonomia is much less common in the very young. One exception is the inherited dysautonomia called Riley-Day syndrome.

Riley-Day Syndrome is inherited in an autosomal recessive fashion, meaning that the parents may not be affected although the child has the disease. Symptoms include postural hypotension, labile blood pressures, poor temperature regulation, hyperhydrosis, cyclic vomiting, emotional lability, and decreased pain sensitivity. These symptoms are probably caused by a failure of normal cellular migration during development.

Trauma and the Autonomic Nervous System

The sympathetic nerves run through the spinal cord in what are called the intermediolateral cell columns. If these columns are interrupted due to trauma with hypotension, loss of sweating, bladder paralysis, and gastrointestinal immotility can result; this is known as spinal shock. Giving naloxone seems to mitigate some of the symptoms: sympathetic and parasympathetic functions will return after a while, but they will no longer be under the control of higher structures. For example, if blood pressure falls, the peripheral blood vessels will not constrict, since this relies on communication between the medulla in the brainstem and the rest of the body through the spinal cord. Other reflexes, however, will remain intact. If the skin is pinched on the arm, for example, the blood vessels in that arm will constrict, resulting in increased pressure in that limb.

People who are tetraplegic as the result of a spinal cord injury may also suffer from what is called autonomic dysreflexia. Blood pressure rises, the heart rate slows, and parts below the lesion may get flushed and perspire excessively, in addition to leg spasms and involuntary emptying of the bladder. Autonomic dysreflexia can be life-threatening if not treated immediately.

Severe head injuries or cerebral hemorrhages can also release adrenal catecholamines and increase sympathetic tone. Sometimes masses can press on the brainstem, leading to intense hypertension, irregular breathing, and heart slowing in what is known as the Cushing response, a grim indicator of increased intracranial pressure.

Dysautonomia Due to Drugs and Toxins

Spinal shock is similar to other autonomic crises called "sympathetic storms," which may be caused by the use of some drugs, such as cocaine. Many prescribed medications work by acting on the autonomic nervous system, and the same is unfortunately true of many toxins. Organophosphate insecticides and sarin, for example, cause parasympathetic overactivity.

Other Dysautonomias

Hyperhydrosis is a less life-threatening, but still potentially embarrassing dysautonomia that results in inappropriately heavy perspiration. In contrast, anhydrosis results in too little sweating, which can be dangerous if it leads to overheating.

Raynaud's phenomenon causes decreased blood flow to fingers in the cold, and is frequently associated with peripheral neuropathy or a connective tissue disease like scleroderma.

Bladder dysfunction is common and may result from many different kinds of problems, including dysautonomias. The innervation of the bladder is complex, and the seemingly simple act of urination actually relies on close cooperation between voluntary, sympathetic, and parasympathetic nerve functions. Perhaps because correct bladder function depends on so many different components, it isn't surprising that problems are common, and can include either incontinence or retention of urine.

It's impossible to address all of the facets of dysautonomia in one article. In addition to what we've covered, sometimes just parts of the body, such as an eye (as in Horner's syndrome) or limb (as in reflex sympathetic dystrophy) can be impacted. This article may serve as a general introduction, and spur further reading for those who want more information.

Sources:

Adams and Victor's Principles of Neurology, 9th ed: The McGraw-Hill Companies, Inc., 2009

Blumenfeld H, Neuroanatomy through Clinical Cases. Sunderland: Sinauer Associates Publishers 2002

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