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Restless legs syndrome (RLS) is a condition in which patients feel compelled to move their legs during rest in response to feelings of discomfort in the legs. Most people with RLS describe a tingling, burning or crawling sensation that is relieved only by moving the legs. However, the relief is usually temporary, requiring patients to move their legs again and again. In some cases, RLS also affects a patient’s arms.

It is not precisely known how many people have RLS. According to the National Institutes of Health (NIH), as many as 12 million Americans may have the condition. Other experts believe that the disorder is underdiagnosed and that the number of people affected is likely to be much higher.

Though RLS does not pose any great danger to a person’s health, patients often find it very uncomfortable. In an attempt to prevent their symptoms, patients often pace the floor, constantly move their legs while sitting (e.g., jiggling or stretching them) or toss and turn in bed. Because symptoms are especially likely to occur at night, many patients report difficulty falling asleep or remaining asleep. Fatigue during the day is commonly associated with RLS because of sleep disturbance.

There are two major types of RLS:

• Primary restless legs syndrome. Also known as idiopathic RLS, it is the result of unknown factors. In most cases, primary RLS is a lifelong condition that can get worse over time. This is especially true when symptoms begin in childhood or early adulthood. Some patients have symptoms that fluctuate, whereas others experience symptoms that are more persistent. This is the more common form of RLS.
  
  
• Secondary restless legs syndrome. This form of RLS is the result of an underlying illness or a side effect of certain medications (e.g., antiseizure medications). It can also occur during pregnancy. Symptoms typically disappear once the patient’s illness subsides, medical condition returns to normal, or after the patient stops taking the inciting medication.  

More than 80 percent of people with RLS also have an associated condition known as periodic limb movement disorder, according to the NIH. In this condition, a person’s legs involuntarily twitch or jerk excessively for about 10 to 60 seconds. As with RLS, symptoms tend to strike at night and may occasionally involve the arms. The cause of this disorder is also unknown.