What is restless leg syndrome?
This disorder, which often appears in otherwise healthy people, is not related to emotional or psychological disorders. Although it affects mostly the legs, as the name suggests, it can also affect the arms. People experience restless legs in many different way, but all describe very unpleasant “creepy, crawly” sensations that occur in the legs when they are sitting or lying still, especially at bedtime. If you have RLS you know it is not like the pain of a leg cramp, or the numbness someone feels if a leg “falls asleep.” RLS sensations are also different from the “pins and needles” or burning feeling a person with diabetes may experience. The uncomfortable feeling of RLS appear most often in the calves of the legs and are temporarily relieved by stretching or moving the legs.

In more severe instances, restless legs syndrome can be painful, or disturbing enough to cause insomnia. The constant need to stretch or move the legs to get rid of the RLS sensations often prevents a person with RLS from falling asleep. As a result, the person may be extremely tired during the day and unable to perform well at work or take part in social activities.

The sleepiness that results from a restless night is not the only daytime problem you might experience if you have RLS. During the day, RLS can interfere with the length of time you can travel by car, airplane, or any other kind of transportation requiring you to sit still for long periods of time. RLS may disturb your ability to sit still at movies, concerts, and in business meetings. The sleep loss and disturbance of daytime activities can make you feel anxiety and depression.

What is periodic limb movement disorder?
Another disorder that affects the limbs as well as a person’s ability to sleep at night and function normally during the day, is periodic limb movement disorder (PLMD), also known as nocturnal myoclonus. While the movement of RLS are a voluntary response to uncomfortable feelings in the limbs when a person is awake, the movements of PLMD occur most often when a person is asleep and are involuntary (that is, not consciously controlled).

People with periodic limb movements are often not aware of these movements, although on rare occasions they may notice the involuntary movements of PLMD while they are still awake. Most people with RLS have periodic limb movements, but patients with PLMD often do not have RLS.

Periodic limb movements usually occur in the legs but may also affect the arms. As the name implies, the movements occur at periodic (regular) intervals, usually every 30 seconds. They typically consist of an extension of the big toe, together with an upward bending of the ankle, knee, or hip. The movements are sometimes similar to jerking or kicking. They usually do not occur continuously throughout the night, but instead cluster in the first half of the night.