myoclonus

Myoclonus is a term for sudden, brief, involuntary muscle jerks or contractions. The movements can involve a single muscle or a muscle group, may occur in clusters, and can be positive (jerks caused by muscle contraction) or negative (brief interruptions in muscle activity). It is a symptom rather than a disease, and can arise from a wide range of disorders affecting the brain, spinal cord, nerves, muscles, or metabolic state, as well as from certain medications or withdrawal.

Classification of myoclonus is based on distribution (focal, segmental, or generalized), rhythm, and presumed anatomical origin. It is commonly grouped as cortical, subcortical, brainstem, or spinal myoclonus, with cortical myoclonus often linked to preceding EEG spikes. Clinical features, such as the context of sleep and response to treatment, aid in recognizing the underlying cause.

Causes are diverse. Physiological forms include sleep starts and hiccups. Pathological myoclonus may accompany epilepsy, neurodegenerative diseases (for example progressive myoclonus epilepsy, Alzheimer's disease, Creutzfeldt–Jakob disease), metabolic disturbances (hepatic or renal failure, electrolyte imbalances), autoimmune or infectious processes, stroke or brain injury, and various drug effects or withdrawal states (including certain antidepressants and opioids).

Diagnosis relies on a detailed history and observation, supported by diagnostic tests such as video-electroencephalography (video-EEG), electromyography (EMG), neuroimaging, and laboratory studies to identify metabolic or infectious etiologies. Treatment targets the underlying condition when possible; symptomatic options include anticonvulsants and sedatives such as valproate, levetiracetam, or clonazepam, as well as botulinum toxin for focal forms and physical therapy. Prognosis varies with cause and may range from self-limited to chronic and disabling.