Periodic Limb Movement Disorder

Periodic Limb Movement Disorder Overview

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.

Periodic Limb Movement Disorder Causes

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)

Periodic Limb Movement Disorder Symptoms

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.