The autonomic nervous system (ANS) regulates physiologic processes.
Regulation occurs without conscious control, i.e., autonomously.
The 2 major divisions are the sympathetic and parasympathetic systems .
Disorders of the ANS can affect any system of the body.
They can originate in the peripheral or central nervous system and may be primary or secondary to other disorders.
The ANS controls
Fluid and electrolyte balance,
Sexual response, and
Many organs are controlled primarily by either the sympathetic or parasympathetic system, although they may receive input from both; occasionally, functions are reciprocal (eg, sympathetic input increases heart rate; parasympathetic decreases it).
The sympathetic nervous system is catabolic and activates fight-or-flight responses. Thus, sympathetic output increases heart rate and contractility, bronchodilation, hepatic glycogenolysis and glucose release, BMR, and muscular strength; it also causes sweaty palms. Less immediately life-preserving functions (eg, digestion, renal filtration) are decreased. Ejaculation is a sympathetic function.
The parasympathetic nervous system is anabolic; it conserves and restores. GI secretions and motility (including evacuation) are stimulated, heart rate is slowed, and BP decreases. Erection is a parasympathetic function.
Two major neurotransmitters in the ANS are acetylcholine and norepinephrine.
Symptoms suggesting autonomic dysfunction include orthostatic hypotension, heat intolerance, and loss of bladder and bowel control.
Erectile dysfunction is an early symptom.
Other possible symptoms include dry eyes and dry mouth, but they are nonspecific.
In a normally hydrated patient, a sustained decrease of > 20 mm Hg in systolic BP or a decrease of > 10 mm Hg in diastolic BP with standing suggests autonomic dysfunction.
Heart rate change with respiration and standing should be noted; absence of physiologic sinus arrhythmia and failure of heart rate to increase with standing indicate autonomic dysfunction.
Miosis and mild ptosis (Horner's syndrome) suggest a sympathetic lesion. A dilated, unreactive pupil (Adie's pupil) suggests a parasympathetic lesion.
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.
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.
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.
Hyperdynamic beta-adrenergic state (irritable heart syndrome); And
Idiopathic hypovolemia (orthostatic anemia).
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.
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.
CAUSES AND SYMPTOMS
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 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 (slowed movement, rigidity) 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.
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.
No test can diagnose multiple system atrophy.
A neurologist makes the diagnosis based on the history of symptoms, a physical examination and by ruling out other causes.
Tests that may help confirm the diagnosis include checking plasma norepinephrine levels and breakdown, and an MRI (magnetic resonance imaging) of the head to rule out other causes.
Parkinsonism (tremors, muscle rigidity)
Cerebellar or corticospinal signs (balance and movement difficulties)
Orthostatic hypotension (drops in blood pressure when body position changes, leading to dizziness, headache, clouding of vision, or fainting)
Urinary incontinence or retention, usually preceding or within two years after the onset of the motor symptoms
Reduced sweating, leading to heat intolerance
Double vision or other vision problems
At present there is no cure for severe autonomic dysfunction.
The goal of treatment is to make the patient more comfortable and preserve bodily functions as long as possible.
The fluctuating blood pressure that is a hallmark of the disorder can make the condition difficult to treat, but medications can be used to control some symptoms.
Dietary changes, such as increasing salt and fluid intake, may help elevate blood pressure.
A breathing or feeding tube may have to be surgically inserted to manage swallowing and breathing difficulties.
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 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.
RECOVERY AND REHABILITATION
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.
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 syndromcan 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.