Periodic Limb Movements in Sleep (PLMs)

Periodic limb movement disorder (PLMD) or periodic leg movements is a sleep disorder characterised by repetitive cramping or jerking movements of the legs that often disturb sleep and cause daytime sleepiness. The condition usually develops after middle age and may coexist with other sleep disorders. Periodic leg movement disorder may be primary in origin without an identified cause or may be associated with medical conditions such as diabetes, sleep apnoea (periods of reduced or arrested breathing during sleep), conditions affecting the spinal cord, and intake or withdrawal of certain medications.

The leg movements are repetitive movements that occur every 20-40 seconds during sleep and usually involve the joints of the knee, ankle and big toe. The limb jerks last about 2 seconds and are often reported by bed partners. Individuals with periodic leg movement disorder experience day time lethargy/sleepiness and restless legs syndrome (a condition characterised by unpleasant sensations in the legs when at rest and an urge to move the legs).

PLMD should not be confused with restless leg syndrome (RLS). RLS occurs while awake as well as when asleep, and when awake, there is a voluntary response to an uncomfortable feeling in the legs. PLMD on the other hand is involuntary, and the patient is often unaware of these movements altogether.

Symptoms

Patients with PLMD will complain of excessive daytime sleepiness, falling asleep during the day, trouble falling asleep at night, and difficulty staying asleep throughout the night. Patients also display involuntary limb movements that occur at periodic intervals anywhere from 20–40 seconds apart. They often only last the first half of the night during non-REM sleep stages. Movements do not occur during REM because of muscle atonia.

To diagnose periodic limb movement, your medical and drug history is reviewed and a thorough physical examination is performed. Possible neurological disorders are ruled out. An overnight sleep study called a polysomnogram may be conducted to identify periodic leg movements or any other sleep disorders. The study measures breathing patterns, air flow, blood oxygen levels, electrical activity of the brain, heart rate, muscular activity, limb and eye movements. Blood and urine tests may also be performed to diagnose underlying medical conditions or identify the presence of drugs.

Periodic leg movements due to secondary causes may be treated by addressing the underlying medical condition. Primary periodic leg movements cannot be completely cured.Your doctor will prescribe medications to reduce the leg movements or help you sleep through the jerks. These medicines usually act on the nervous system by reducing muscle contractions regulating muscle movements, or intensifying sleep.

Talk with your doctor if you have any questions about your medications or notice any side effects.