Periodic Limb Movement Disorder
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. "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.
PLMD can occur at any age. Like many sleep disorders, PLMD is more common in middle-aged and older people. For more information on Periodic Limb Movement Disorder, go to www.emedicinehealth.com