Epileptic negative myoclonus in herpes simplex virus encephalitis

Epileptic negative myoclonus (ENM) is a rarely reported clinical seizure semiology. It is defined as a brief interruption of tonic muscle activity in association with an epileptiform discharge on the EEG (spike or sharp wave) without preceding myoclonia. The diagnosis of ENM requires a polygraphic recording with EEG and surface EMG electrodes covering the affected body part(s), while the muscles have tonic activity. Historically, ENM has been reported in a variety of chronic epilepsy syndromes such as benign epilepsy with centrotemporal spikes, progressive myoclonic epilepsy syndromes, symptomatic partial epilepsy syndromes due to structural pathologies, cryptogenic epilepsies, etc. In this paper, we report a patient with herpes simplex virus encephalitis who presented with multiple different seizure types including ENM. The patient showed significant improvement after treatment with acyclovir.