context: Periodic limb movement disorder ( PLMD) is repetitive cramping or jerking of the legs during sleep. It is the only movement disorder that occurs only during sleep, and it is sometimes called periodic leg (or limb) movements during sleep. " Periodic" refers to the fact that the movements are repetitive and rhythmic, occurring about every 20-40 seconds. PLMD is also considered a sleep disorder, because the movements often disrupt sleep and lead to daytime sleepiness. PLMD may occur with other sleep disorders. It is often linked with restless legs syndrome, but they are not the same thing. Restless legs syndrome is a condition involving strange sensations in the legs (and sometimes arms) while awake and an irresistible urge to move the limbs to relieve the sensations. At least 80% of people with restless legs syndrome have PLMD, but the reverse is not true. When PLMD was first described in the 1950s, it was called nocturnal myoclonus. Nocturnal means night, and myoclonus is a rapid, rhythmic contraction of a group of muscles similar to that seen in seizures. PLMD movements are not myoclonus, however, and the original name is not used today. PLMD can occur at any age. Like many sleep disorders, PLMD is more common in middle-aged and older people. Persistent sleep disruption and daytime sleepiness are not part of normal aging. Periodic limb movement disorder can be primary or secondary. Secondary PLMD is caused by an underlying medical problem. Primary PLMD, on the other hand, has no known cause. It has been linked to abnormalities in regulation of nerves traveling from the brain to the limbs, but the exact nature of these abnormalities is not known. Secondary PLMD has many different causes, including the following. Many of these are also causes of restless legs syndrome. Diabetes mellitus Iron deficiency Spinal cord tumor Spinal cord injury Sleep apnea syndrome - Breathing difficulties that disrupt sleep, causing daytime sleepiness and a number of other problems Narcolepsy - A sleep disorder involving excessive sleepiness and overpowering urge to sleep during waking hours Uremia - Build-up of waste products in the blood because of poor kidney function Anemia - Low level of hemoglobin, the substance that carries oxygen in the blood Medication - Neuroleptics and other antidopaminergic agents such as Haldol, dopaminergic agents such as Sinemet (despite the fact that Sinemet is often a treatment for PLMD), or tricyclic antidepressants such as amitriptyline ( Elavil) Withdrawal from sedative medications such as barbiturates or benzodiazepines (such as Valium) The most common symptoms noted by people with PLMD are not leg movements but poor sleep and daytime sleepiness. Many people with PLMD are unaware of their leg movements unless their bed partner tells them. Leg movements involve one or both limbs. Typically the knee, ankle, and big toe joints all bend as part of the movements. The movements vary from slight to strenuous and wild kicking and thrashing. The movements last about 2 seconds (and thus are much slower than the leg jerks of myoclonus). The movements are rhythmic and repetitive and occur every 20-40 seconds. In most people with PLMD, poor sleep and daytime sleepiness are the most bothersome symptoms. Many people do not link their sleep problem with leg movements. Sleep disturbance has many different causes. Depending on how you describe your symptoms, your health care provider may ask you many detailed questions. These questions concern your medical problems now and in the past, family medical problems, medications you take, your work and travel history, and your habits and lifestyle. A detailed physical examination will look for signs of an underlying cause for your sleep problem. There is no lab test or imaging study that can prove that you have PLMD. However, certain tests can identify underlying medical causes such as anemia, other deficiencies, and metabolic disorders that could cause PLMD. You may have blood drawn to check your blood cell counts and hemoglobin, basic organ functions, chemistry, and thyroid hormone levels. You also may be checked for certain infections that could cause secondary PLMD. A urine sample may be collected to check for traces of drugs that can cause sleep problems. Polysomnography (sleep lab testing) is the only way to confirm that you have PLMD. As you sleep in the lab, your leg movements can be documented. At any time during your evaluation, your health care provider may refer you to a neurologist (a specialist in disorders of the nervous system). This specialist can help rule out other neurological problems and confirm the diagnosis of PLMD. Treatment does not cure the disorder but usually relieves symptoms. Treatment involves medication that either reduces the movements or helps the person sleep through the movements. Therapy does not cure PLMD but relieves symptoms. Note that many of the medications used to treat PLMD are the same as those used to treat restless legs syndrome. Benzodiazepines: These drugs suppress muscle contractions. They are also sedatives and help you sleep through the movements. Clonazepam ( Klonopin), in particular, has been shown to reduce the total number of periodic limb movements per hour. It is probably the most widely used drug to treat PLMD. Dopaminergic agents: These drugs increased the levels of an important neurotransmitter (brain chemical) called dopamine, which is important in regulating muscle movements. These medications seem to improve the condition in some people but not in others. Widely used examples are a levodopa/carbidopa combination ( Sinemet) and pergolide ( Permax). Anticonvulsant agents: These medications reduce muscle contractions in some people. The most widely used anticonvulsant in PLMD is gabapentin ( Neurontin). GABA agonists: These agents inhibit release of certain neurotransmitters that stimulate muscle contractions. The result is relaxation of contractions. The most widely used of these agents in PLMD is baclofen ( Lioresal). Your health care provider will ask you to return for one or more follow-up visits after trying his or her recommendations. It is very important that your bed partner understand the nature of PLMD and that you are not intending to injure him or her with your movements. See your health care provider regularly for proper care of any medical or mental problems. Primary PLMD may be chronic (permanent). Many people with primary PLMD have improved nighttime sleep (remission) but experience one or more relapses over time. Secondary PLMD may cease with treatment of the underlying cause. American Academy of Sleep Medicine 2510 North Frontage Avenue Darien, IL 60561 (630) 737-9770 National Sleep Foundation 1010 N. Glebe Rd, Suite 310 Arlington, VA 22201 (703) 243-1697 Restless Legs Syndrome Foundation, Inc. 1530 Greenview Dr SW, Suite 210 Rochester, MN 55902-2985 (507) 287-6465 leg jerking, nighttime kicking, nighttime leg movements, nocturnal myoclonus, periodic leg movements during sleep, PLMD, restless legs syndrome, sleep disorder, parasomnias, daytime sleepiness, myoclonus, periodic limb movement disorder, disorders that disrupt sleep, disrupted sleep, insomnia