Myoclonus is a sudden, short-lived, lightning-fast and involuntary movement. The incidence of myoclonus is estimated to be 1–3/100,000 people. It is classified in several ways: according to the cause (physiological, essential, epileptic, symptomatic), affected anatomical structures (cortical, subcortical, spinal, peripheral nerve or root), extension (focal, segmental, multifocal, generalized) and clinical features (rhythmic, irregular, repetitive) and in relation to activity (spontaneous, action, reflex).
Physiological myoclonus occurs in healthy people (for example: myoclonus during sleep and anxiety-induced myoclonus). Essential myoclonus is a hereditary (autosomal dominant inheritance) or sporadic disorder manifested by multifocal myoclonic jerks originating in the subcortical regions. It begins before the age of 20 and has a benign course with the absence of other neurological disorders. Epileptic myoclonus is characterized by the existence of epileptic seizures in addition to myoclonic jerks as part of numerous epilepsies. Symptomatic myoclonisms often with progressive encephalopathy, dementia, extrapyramidal signs and other symptoms are the result of a large number of different causes (neurodegenerative diseases, dementia, paraneoplastic syndromes, peripheral nerve lesions, viral, metabolic causes, structural brain lesions, the influence of toxins, drugs, drug). According to the frequency the most common is symptomatic or secondary myoclonus followed by epileptic myoclonus while essential primary myoclonus is relatively rare.