http://sleep.health.am/sleep/more/pe...ts-in-sleep/#5

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.

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.

Furthermore, many patients with PLMS also suffer from other sleep disorders, including SDB and REM sleep behavior disorder.