Autonomic dysfunction

Definition

Dysfunction of the autonomic nervous system (ANS) is known as dysautonomia. The autonomic nervous system regulates unconscious body functions, including heart rate, blood pressure, temperature regulation, gastrointestinal secretion, and metabolic and endocrine responses to stress such as the "fight or flight" syndrome. As regulating these functions involves various and multiple organ systems, dysfunctions of the autonomic nervous systems encompass various and multiple disorders.

Description

The autonomic nervous system consists of three subsystems: the sympathetic nervous system, the parasympathetic nervous system and the enteric nervous system. The ANS regulates the activities of cardiac muscle, smooth muscle, endocrine glands, and exocrine glands. The autonomic nervous system functions involuntarily (reflexively) in an automatic manner without conscious control.

In contrast to the somatic nervous system that always acts to excite muscles groups, the autonomic nervous systems can act to excite or inhibit innervated tissue. The ANS achieves this ability to excite or inhibit activity via a dual innervation of target tissues and organs. Most target organs and tissues are innervated by neural fibers from both the parasympathetic and sympathetic systems. The systems can act to stimulate organs and tissues in opposite ways (antagonistic). For example, parasympathetic stimulation acts to decrease heart rate. In contrast, sympathetic stimulation results in increased heart rate. The systems can also act in concert to stimulate activity. The autonomic nervous system achieves this control via two divisions: the sympathetic nervous system and the parasympathetic nervous system. Dysfunctions of the autonomic nervous system are recognized by the symptoms that result from failure of the sympathetic or parasympathetic components of the ANS.

Primary dysautonomias include multiple system atrophy (MSA) and familial dysautonomia. The dysfunction can be extensive and manifest as a general autonomic failure or can be confined to a more localized reflex dysfunction.

With multiple system atrophy, a generalized autonomic failure, male patients experience urinary retention or incontinence and impotence (an inability to achieve or maintain a penile erection). Both males and females experience ataxia (lack of muscle coordination) and a dramatic decline in blood pressure when they attempt to stand (orthostatic hypotension ). Symptoms similar to Parkinson's disease may develop, such as slow movement, tremors , and stiff muscles. Visual disturbances , sleep disturbances, and decreased sweating may also occur.

Persons with autonomic dysfunction who do not exhibit the classical symptoms of orthostatic hypotension may exhibit a less dramatic dysfunction termed orthostatic intolerance. These patients experience a milder fall in blood pressure when attempting to stand. However, because the patients have an increased heart rate when standing, they are described as having postural tachycardia syndrome (POTS).

Although not as prevalent in the general population as hypertension, orthostatic intolerance is the second most common disorder of blood pressure regulation and is the most prevalent autonomic dysfunction. Orthostatic hypotension and orthostatic intolerance can result in a wide array of disabilities. Common orthostatic intolerance syndromes include: hyperadrenergic orthostatic hypotension (partial dysautonomia); orthostatic tachycardia syndrome (sympathicotonic orthostatic hypotension); postural orthostatic tachycardia syndrome (mitral valve prolapse syndrome); postural tachycardia syndrome (soldier's heart); hyperadrenergic postural hypotension (vasoregulatory asthenia); sympathotonic orthostatic hypotension (neurocirculatory asthenia); hyperdynamic beta-adrenergic state (irritable heart syndrome); and idiopathic hypovolemia (orthostatic anemia).

Demographics

Milder forms of autonomic dysfunction such as orthostatic intolerance affect an estimated 500,000 people in the United States. Orthostatic intolerance more frequently affects women; female-to-male ratio is at least 4:1. It is most common in people less than 35 years of age. More severe forms of dysautonomia such as multiple system atrophy often occur later in life (average age of onset 60 years) and affect men four times as often as women.

Causes and symptoms

Symptoms of the autonomic dysfunction of orthostatic intolerance include lightheadedness, palpitations, weakness, and tremors when attempting to assume an upright posture. Less frequently, patients experience visual disturbances, throbbing headaches, and often complain of fatigue and poor concentration. Some patients report fainting when attempting to stand.

The cause of lightheadedness, fainting, and similar symptoms is a lack of adequate blood pressure in the cerebral circulatory system.

In addition to orthostatic hypotension and Parkinson-type symptoms, persons with multiple systems atrophy may have difficulty articulating speech, sleep apnea and snoring, pain in the back of the neck, and fatigue. Eventually, cognitive (mental reasoning) ability declines in about 20% of cases. Multiple systems atrophy occurs sporadically and the cause is unknown.

Diagnosis

Diagnosis of orthostatic intolerance is made when a patient experiences a decrease of blood pressure (not exceeding 20/10 mm Hg) when attempting to stand and a heart rate increase of less than 30 beats per minute.

Diagnosis of other types of dysautonomia is difficult, as the disorders are varied and mimic other diseases of the nervous system. As Parkinsonism is the most frequent motor deficit seen in multiple systems atrophy, it is often misdiagnosed as Parkinson's disease. Magnetic resonance imaging (MRI) of the brain can sometimes detect abnormalities of striatum, cerebellum , and brainstem associated with multiple systems atrophy. But in up to 20% of MSA patients, MRI of the brain is normal. A test with the drug clonidine has also been used to differentiate Parkinson's disease from multiple systems atrophy, as certain hormone levels in the blood will increase in persons with Parkinson's disease after clonidine administration, but not in persons with multiple systems atrophy. Symptoms such as severe dysarthria (difficulty articulating speech) and stridor (noisy inspiration) alert the physician to the possibility of multiple systems atrophy, as they occur in the disorder, but are rare in Parkinson's disease.

Treatment team

Caring for a person with a disorder of the autonomic nervous system requires a network of health professionals, community resources, and friends or family members. A neurologist usually makes the diagnosis, and the neurologist and primary physician coordinate ongoing treatment and symptom relief. Physical, occupational, speech, and respiratory therapists provide specialized care, as do nurses. Social service and mental health consultants organize support services.

Treatment

At present there is no cure for severe autonomic dysfunction. Treatment is centered on the remediation of symptoms, patient support, and the treatment of underlying diseases and disorders in cases of secondary autonomic dysfunction. In many cases, cure or an improvement in the underlying disease or disorder improves the patient prognosis with regard to remediation of autonomic dysfunction symptoms.

With regard to orthostatic hypotension, drug treatment includes fludrocortisone, ephedrine, or midodrine. Medications are accompanied by postural relief such as elevation of the bed at the head and by dietary modifications to provide some relief for the symptoms of dizziness and tunnel vision.

In multiple systems atrophy, anti-Parkinson medications such as Sinemet often help with some of the symptoms of muscle rigidity and tremor, and create an overall feeling of well-being. Medications used in the treatment of orthostatic hypotension tend to not perform as well in this group; although they elevate the blood pressure while standing, they decrease the blood pressure while reclining.

Recovery and rehabilitation

Recovery from some dysautonomias can be complicated by secondary conditions such as alcoholism, diabetes, or Parkinson's disease. Some conditions improve with treatment of the underlying disease, while only halting of the progression of symptoms is accomplished in others. Some mild dysautonomias stabilize and, with treatment, cause few limitations to daily activities.

Overall, as there are no cures for most severe or progressive dysautonomias, the emphasis is instead placed upon maintaining mobility and function for as long as possible. Aids for walking and reaching, positioning devices, and strategies for maintaining posture, balance, and blood pressure while rising can be provided by physical and occupational therapists. Speech and nutritional therapists can devise diets and safe strategies for eating, and recommend tube feedings if necessary.

Clinical trials

As of mid-2004, the Mount Sinai Medical Center in New York was recruiting participants for a study related to a new drug for the treatment of multiple systems atrophy. Persons interested in participating in the study (Droxidopa in Treating Patients With Neurogenic Hypotension) should contact the study recruiting coordinator Horacio Kaufmann at telephone: (212) 241-7315. Additional trials for the study and treatment of multiple systems atrophy and other dysautonomias can be found at the National Institutes of Health website for clinical trials : <http://www.clinicaltrials.gov>.

Prognosis

The prognosis for persons suffering autonomic dysfunction is variable and depends on specific dysfunction and on the severity of the dysfunction. Autonomic dysfunctions can present as acute and reversible syndromes, or can present in more chronic and progressive forms. Persons with orthostatic intolerance can usually maintain a normal lifespan and active lifestyle with treatment and minimal coping measures, while persons with multiple systems atrophy usually have a lifespan of about 5–7 years after diagnosis.

Resources

BOOKS

Goldstein, David S., and Linda J. Smith. The NDRF Handbook for Patients with Dysautonomias. Malden, MA: Blackwell Futura Media, 2002.

OTHER

"Disorders of the Autonomic Nervous System." National Dysautonomia Research Foundation. May 16, 2004 (May 22, 2004). <http://www.ndrf.org/autonomic_disorders.htm>.

"NINDS Dysautonomia Information Page." National Institute of Neurological Disorders and Stroke. May 16, 2004 (May 22, 2004). <http://www.ninds.nih.gov/health_and_medical/disorders/dysauto_doc.htm>.

ORGANIZATIONS

Dysautonomia Foundation. 633 Third Avenue, 12th Floor, New York, NY 10017-6706. (212) 949-6644; Fax: (212) 682-7625. [email protected]. <http://www.familialdysautonomia.org>.

Familial Dysautonomia Hope Foundation, Inc. (FD Hope). 1170 Green Knolls Drive, Buffalo Grove, IL 60089. (828) 466-1678. [email protected]. <http://www.fdhope.org>.

National Dysautonomia Research Foundation. 1407 West 4th Street, Red Wing, MN 55066-2108. (651) 267-0525; Fax: (651) 267-0524. [email protected]. <http://www.ndrf.org>.

National Organization for Rare Disorders (NORD). P.O. Box 1968 (55 Kenosia Avenue), Danbury, CT 06813-1968. (203) 744-0100 or (800) 999-NORD; Fax: (203) 798-2291. [email protected]. <http://www.rarediseases.org>.

Shy-Drager/Multiple System Atrophy Support Group, Inc. 2004 Howard Lane, Austin, TX 78728. (866) 737-4999 or (800) 999-NORD; Fax: (512) 251-3315. [email protected]. <http://www.shy-drager.com>.

Paul Arthur