Definition of Periodic Limb Movements (PLM)

Periodic Limb Movementse (PLM) - or nocturnal myoclonus - is characterized by episodes of limb movements that typically recur at intervals of 15 to 40 seconds during Non-REM sleep. The movements usually involve the legs, but sometimes the arms as well. Episodes generally last from five minutes to two hours and alternate with periods of normal sleep. It is not the same as "hypnic jerks" which startle many of us as we fall asleep. The victim of myoclonus is usually unaware of leg movements, but complains of fragmented and unrefreshing sleep.