Negative myoclonus refers to an abrupt involuntary movement caused by sudden, brief interruptions of muscle activity. Recently, the Task Force on Classification and Terminology of the International League against Epilepsy recognized negative myoclonus as a seizure type, defining it as an “interruption of tonic muscle activity for less than 500 ms without evidence of preceding myoclonia.” Clinically, negative myoclonus is classified into four types: asterixis, postural lapses, epileptic negative myoclonus, and physiologic negative myoclonus. Asterixis, which usually occurs in metabolic or toxic encephalopathies, is considered to be subcortical in origin but the cerebral cortex may be involved in some cases.
Examination shows an irregular distal upper extremity tremor and sudden jerks involving the hands and fingers bilaterally. When he maintains his hands in an extended posture, the jerky involuntary movements worsen and resemble a flapping tremor. There is an action tremor during finger-nose testing.
Negative myoclonus.mp4 (MP4 20,491KB)