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Experts speculate that restless legs syndrome (RLS) may result from an imbalance of the brain chemical dopamine. This chemical transmits signals in parts of the brain that control muscle movement. Stress may also play a role in RLS, because symptoms often worsen during periods of stress.

When a cause for RLS is unknown (idiopathic), as it is in a majority of cases, a physician will diagnose the patient with primary RLS. This form of RLS tends to run in families, and people whose parents have the condition have a higher risk of developing RLS.

In a smaller number of cases, RLS can be traced to an underlying condition. This form of the disorder is diagnosed as secondary RLS. Pregnancy is one of the chief causes of secondary RLS, which is most likely to occur during the third trimester. Other conditions that may cause secondary RLS include:

• Diabetic neuropathy
  
  

  

• Other forms of nerve damage in the limbs (peripheral neuropathy)
  
• Iron deficiency and anemia
  
• Other mineral or vitamin deficiencies
  
• Fibromyalgia
  
• Kidney failure with resulting uremia (formation of urea and other wastes in the blood)
  
• Parkinson’s disease
  
• Rheumatoid arthritis

The use of certain medications can also trigger RLS. These include certain anti-seizure (anticonvulsant) and anti-nausea drugs, antidepressants, antipsychotics and some cold and allergy medications, notably antihistamines. Finally, lifestyle choices such as use of tobacco or excessive consumption of alcohol or caffeine may worsen symptoms of RLS.

Women appear to be affected more than men. In particular, women who are pregnant have increased rates of RLS. The disorder is diagnosed across all racial and ethnic groups but appears to be more common in people of northern European descent.

About two of every five cases of this disorder are diagnosed in people under the age of 20. Nonetheless, the incidence of RLS increases as people become older, with many diagnosed in middle age. When RLS first appears later in life, symptoms are usually more frequent and severe. In these cases, RLS is likely to be the result of a medical condition.