Restless leg syndrome (RLS) is a metabolic sleep disorder that causes feelings in the legs that sufferers have described using words such as: tingling, numbness, pins and needles, tiredness, itching, uneasiness, pain, cramping, aching, burning, creeping, crawling, simply indescribable...

These feelings happen during rest or sleep, especially in the lower legs, and create an urge to move the legs about as a way of relieving or completely getting rid of these feelings. If a person with restless leg syndrome tries to hold the legs still and not move them, the feelings only seem to get worse. Restless leg syndrome does not cause any damage to one's health, but it very often leaves the sufferer feeling drowsy during the daytime from not getting a good night's sleep. People who have severe restless leg syndrome may feel a kind of spastic flexing of their hips, knees and ankles when they lie down, as well as leg pains in the morning after they get out of bed. While restless leg syndrome can be a problem at any age, it seems to be most serious in people who are middle-aged and older.

The exact cause of restless leg syndrome is unknown. There may be many different causes, including important underlying nutritional issues which will need to be resolved before symptoms improve. RLS tends to run in families. Although most cases of restless leg syndrome happen in healthy people, there is an increased chance of the syndrome occurring in people who have diabetes or chronic alcoholism, or who are pregnant. Cases of restless leg syndrome caused by pregnancy usually clear up after delivery of the baby.

According to a study, about half the cases of restless legs syndrome are caused by defects in a single gene. Researchers at the Max Planck Institute of Psychiatry in Munich, Germany, found that when restless legs syndrome (RLS) appears before the age of 30, it is likely caused by a single, yet-unidentified gene. In cases in which the syndrome appears after the age of 30, a combination of various genes and environmental causes is probably to blame.

The best treatment can often be arrived at only by active experimentation by the patient or in cooperation with a doctor who may wish to perform laboratory testing.

Periodic limb movement disorder (PLMD) and restless leg syndrome (RLS) are distinct disorders, but often occur simultaneously. Both PLMD and RLS are also called (nocturnal) myoclonus, which describes frequent or involuntary muscle spasms. Periodic limb movement was formally described first in the 1950s, and, by the 1970s, it was listed as a potential cause of insomnia. In addition to producing similar symptoms, PLMD and RLS are treated similarly.

Periodic limb movement disorder (PLMD) affects people only during sleep. The condition is characterized by behavior ranging from shallow, continual movement of the ankle or toes, to wild and strenuous kicking and flailing of the legs and arms. Furthermore, abdominal, oral, and nasal movement sometimes accompanies PLMD. Movement of the legs is more typical than movement of the arms in cases of PLMD. Movements typically occur for 0.5 to 10 seconds, in intervals separated by five to 90 seconds.

In 1979, the Association of Sleep Disorder Centers (ASDC) set the parameters for determining the presence of PLMD: A formal diagnosis of nocturnal myoclonus requires three periods during the night, lasting from a few minutes to an hour or more, each containing at least 30 movements followed by partial arousal or awakening. Today, these parameters are a bit more relaxed, and PLMD usually includes any repetitive, involuntary movement during the night.

The incidence of PLMD increases with age. It is estimated to occur in 5% of people age 30 to 50 and in 44% of people over the age of 65. As many as 12.2% of patients suffering from insomnia and 3.5% of patients suffering from excessive daytime sleepiness may experience PLMD.