Myoclonus is the sudden involuntary contraction or relaxation of a muscle or group of muscles. Myoclonus is not a disease but a sign of several diseases or conditions that affect the brain or spinal cord. It can be mild, affecting only a single muscle, or more severe, affecting groups of muscles throughout the body.

It can be caused by epilepsy, brain tumors, head or spinal cord injuries, stroke, infections, kidney or liver failure, lipid storage disease, loss of oxygen to the brain, and chemical poisoning.

Myoclonus is typically treated with barbiturates, which slow down the action of the central nervous system.