• Definition and Prevalence
• Consequences of the Disorder
• Clinical Presentation
• Risk Factors
• Diagnosis and Differential Diagnosis
• Treatment and Management

Definition and Prevalence
Periodic limb movements in sleep (PLMS) is a disorder of unknown etiology, in which patients involuntarily kick their limbs (most often it is their legs) in short, clustered episodes lasting between 0.5 and 5 s and occurring about every 20 to 40 s. The kicks are often accompanied by arousals. These episodes occur repeatedly throughout the night. The myoclonus index (MI) represents the number of kicks with arousals per hour of sleep.

The prevalence of PLMS seems to increase with age. Ancoli-Israel et al. reported that 45% of randomly selected elderly adults aged 65 years and older had PLMS, compared to 5% to 6% of the younger adult population.

Consequences of the Disorder
As with SDB, the nighttime arousals are often too short to be recalled. However, patients with PLMS may complain of insomnia, as they may have difficulty falling asleep as well as settling back to sleep following these episodes. PLMS occur most often in the first half of the night, during sleep stages 1 and 2. Sleep is fragmented, with reduced amounts of stages 3 and 4 and REM.

Clinical Presentation
In addition to complaining of difficulty falling asleep, patients may also complain of excessive daytime sleepiness, as they suffer from sleep fragmentation throughout the night. They may also note that the bedding is disorganized or jumbled when they wake up in the morning. Bed partners often complain of the leg kicks disturbing their sleep as well, and often it is important to obtain information from the bed partner in diagnosing and assessing the disorder.

Risk Factors
A related disorder that occurs during the relaxed, awake state often just before sleep onset is restless leg syndrome (RLS). Patients report unpleasant sensations in their legs and irresistible movement of the legs. The disagreeable, sometimes painful leg sensations are alleviated by rubbing or squeezing the legs or simply by walking. The prevalence of RLS is not well defined. Most patients with RLS also suffer from PLMS, suggesting that these disorders may be related. Furthermore, many patients with PLMS also suffer from other sleep disorders, including SDB and REM sleep behavior disorder.

Diagnosis and Differential Diagnosis
PLMS is diagnosed in a full night sleep recording in the sleep clinic, which includes the recording of the anterior tibialis muscles to establish the MI. The muscular jerks are often accompanied by EEG signs of arousal, which may appear following the leg jerks. As with SDB, ambulatory equipment is available to record sleep in the comfort of one’s own home. PLMS is diagnosed with a MI greater than 5.

PLMS and RLS may be associated with some medical conditions, including uremia, anemia, chronic lung disease, myelopathies, and peripheral neuropathies. Use of medications, such as tricyclic antidepressants and lithium carbonate, and withdrawal from benzodiazepines and anticonvulsants may all induce these disorders. Other movement disorders that should be differentiated from PLMS include the hypnic myoclonus, nocturnal leg cramps, and jerks associated with long-term use of l-dopa.

Treatment and Management
PLMS is treated by medications aimed at reducing or eliminating the leg jerks or the arousals. Dopaminergic agents such as carbidopa/levodopa, pergolide, and a newer drug, pramipexol, are the treatment of choice for PLMS, as they decrease or eliminate both the leg jerks and the arousals. These medications are also successful for the treatment of RLS. In one study, carbidopa/ levodopa was superior to propoxyphene in decreasing the number of leg kicks and the number of arousals per hour of sleep. However, carbidopa/levodopa and, to a lesser extent, pergolide may shift the leg movements from the nighttime to the daytime.

Benzodiazepines, such as clonazepam and temazepam, are sometimes used to treat PLMS. These drugs do not eliminate the limb movements but do decrease the arousals, so that the patient sleeps more continuously throughout the night. Triazolam has been shown to be effective in older patients, although because of age-related changes in pharmacokinetics and the need to avoid daytime sedation, it is recommended that low doses of triazolam be prescribed in this population. Furthermore, caution should be used in prescribing a sedative hypnotic to elderly patients who might have SDB, because sedatives exacerbate the severity of the respiratory events. Some of the longer-acting medications, particularly clonazepam, may not be eliminated by morning, particularly in older adults, causing daytime sedation. Opiates such as propoxyphene or Tylenol with codeine are effective in decreasing the leg kicks; however, the arousals may continue to occur.