Restless Legs Syndrome and Other Sleep-Related Leg Disorders

Description

Alternative Names

Causes

The primary cause of restless legs syndrome is not known. Researchers are investigating neurologic problems that may arise either in the spinal cord or the brain. One current theory on the cause of restless legs syndrome involves a deficiency in a brain chemical called dopamine. RLS probably has a genetic basis in many cases, particularly those that develop before age 40. When the onset of the condition occur in older adults, it most likely due to some neurologic problem.

The central nervous system is comprised of the brain and spinal cord. The peripheral nervous system includes all peripheral nerves.

Genetic Factors

People with restless legs syndrome often have a family history of the disorder. Researchers, however, have had little luck to date in detecting any specific genetic locations or factors that might be responsible for this condition. Of some promise are some studies of families with a strong history of RLS-related conditions. For example, research on Canadian and Italian families with RLS have led to identification of locations for genetically-based RLS on chromosomes 12 and 14.

Neurologic Abnormalities

Dopamine and Neurologic Abnormalities in the Brain. Other research suggests that neurologic abnormalities involved with RLS and PLMD originate in the brain. A variety of studies support the hypothesis that an imbalance in neurotransmitters (chemical messengers in the brain), notably dopamine and serotonin, may play a part in RLS.Dopamine and serotonin unleash an array of nerve impulses that affect muscle movement. A similar effect is seen in Parkinsons disease, and indeed, drugs that increase dopamine are used for both disorders. (It should be noted that Parkinsons disease itself does not seem to increase the risk for RLS. Nor does RLS early in life predispose to Parkinsons later on. The two diseases then do not appear to share the same mechanisms.)

Neurologic Abnormalities in the Spine. Some research suggests that restless legs syndrome may be due to nerve impairment in the spinal cord. It had been thought that such abnormalities were likely to originate from nerve pathways in the lower spine. However, some patients with RLS commonly have symptoms in the arms suggesting that the upper spine may be involved as well. One 2001 study suggested that in patients with RLS and PLMD there is an abnormal over-excitable response along the entire spinal cord, which is triggered by sleep-related factors.

Neuropathy. Some experts suggest that RLS, particularly if it occurs in older adults, may be a form of neuropathy, which is an abnormality in the nervous system outside the spine and brain. Nevertheless, there is no evidence of a causal relationship.

Deficiencies in Iron Metabolism

Iron deficiency, even at a level too mild to cause anemia, has been linked to RLS in some people.Studies suggest, in fact, that RLS in some people may be due to impaired iron acquisition in cells that regulate dopamine in the brain. (Dopamine abnormalities are known to play a role in RLS.) Some studies have reported RLS in between 25% and 30% of people with low iron levels. (In fact, the common connection between RLS and Parkinson's disease may derive from iron deficiencies in these patients.

Causes of Periodic Limb Movement Disorder (PLMD)

The cause or causes of PLMD are not clear. Some work suggests that it may be due to abnormalities in the autonomic nervous system (which regulates the involuntary actions of the smooth muscles, heart, and glands).