Nocturnal myoclonus, or periodic limb movement disorder (PLMD), is a sleep disorder characterized by sudden muscle contractions or relaxation during sleep. PLMD can cause sleep disturbances and daytime sleepiness. Diagnosis is made through a sleep study and anecdotal evidence. Treatment includes dopaminergic drugs and low doses of Clonazepam®. Risk factors include age, gender, and other underlying health conditions.
Nocturnal myoclonus, also known as periodic limb movement disorder or PLMD, is a form of myoclonus in which symptoms of the disorder occur during sleep. Myoclonus is itself a symptom of disease, rather than a diagnosis, manifesting as sudden muscle contractions or muscle relaxation. Muscle contraction or relaxation can occur in response to a trigger or it can occur randomly. Occasional involuntary muscle contractions and hiccups are examples of nondisordered myoclonus.
Many people who experience nocturnal myoclonus have no accompanying negative side effects. They can simply move their limbs during sleep without being disturbed by the movement. In these cases the person is said to have periodic limb movements during sleep, or PLMS. This is not the same as PLMD, as PLMS is not a disorder in itself and does not always require treatment. PLMS is, however, a symptom of PLMD.
Nocturnal myoclonus is classified as a sleep disorder and can cause symptoms during the night and side effects during waking hours. The disorder can cause nighttime sleep disturbances, insomnia, and sleepiness during waking hours. People who experience multiple episodes of periodic limb movements during sleep over several nights, as well as sleep disturbances and side effects during waking hours, can be diagnosed with PLMD.
The diagnosis of PLMD is made based on anecdotal evidence from a patient’s partner or other close relatives or friends, as well as the results of a polysomnogram. Polysomnography, or a sleep study, is a test that records the biological and physiological changes that occur when a person sleeps. The test is performed during the patient’s normal sleeping hours and records brain function, eye movements, muscle activity and heart rhythm.
An estimated 4% of people have PLMS. The percentage increases with increasing age, and women are more likely to be affected than men. Up to 11% of older women can be affected. There is also evidence that PLMS is related to restless legs syndrome. One study found that up to 80 percent of people with restless legs syndrome also had PLMS.
Risk factors for nocturnal myoclonus, particularly in the absence of restless legs syndrome, are varied. These include drinking coffee, snoring, stress, using hypnotics, and shift work. Several risk factors are associated with restless legs syndrome and PLMD, including obstructive sleep apnea, musculoskeletal disease, heart disease, catalepsy, and mental disorders.
Treatments for nocturnal myoclonus are aimed at reducing the incidence of leg spasms caused by muscle contraction or relaxation and at reducing the incidence of awakening during sleep. Dopaminergic drugs, which are drugs that stimulate dopamine receptors, are helpful in treating both symptoms. Low doses of a drug called Clonazepam® can also help improve sleep quality.
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