Transient Myoclonic State with Asterixis: Primary Motor Cortex Hyperexcitability is Correlated with Myoclonus

Abstract

Objective To clarify the clinical features and mechanism of the transience of myoclonus in patients with a transient myoclonic state with asterixis (TMA). Methods We investigated the clinical and eletrophysiological profiles of 6 patients with TMA (age: 84±3 years). During an asymptomatic period, somatosensory evoked potentials (SEPs) were recorded in all 6 patients and motor evoked potentials (MEPs) were examined in 1 patient. SEPs were recorded and jerk-locked back averaging (JLA) was performed in 2 patients while symptomatic. SEPs were also recorded from 8 aged control subjects (age: 68±5 years). Results All TMA patients had mild chronic systemic diseases. During an asymptomatic period, SEP amplitudes were not significantly enlarged in comparison with control subjects, and MEPs were normal. Examination of 2 patients during symptomatic period indicated no enlargement of SEP amplitudes and JLA disclosed a positive spike preceding myoclonic jerks. In one of these patients, the amplitude of the positive spike decreased once myoclonus improved. Conclusion TMA occurred in aged patients with mild chronic systemic diseases. JLA findings and the absence of giant SEPs further support that TMA is a cortical non-reflex myoclonus. In addition, transient hyperexcitability at the primary motor cortex disclosed by JLA correlated well with its transient symptoms.

Transient myoclonic state with asterixis presenting as persistent hyperperfusion on single‐photon emission computed tomography: A case report

“…The clinical manifestations of the patient were consistent with TMA. In previous electrophysiological studies, myoclonus in patients with TMA correlated with cortical hyperexcitability selectively in the primary motor cortex during the symptomatic period . Also in the present case, similar etiology was supported by hyperperfusion of the precentral gyri on 123 I‐IMP SPECT.…”

“…The symptoms disappear within a few days by treatment with benzodiazepines, but they often recur . When symptoms appear, hyperexcitability in the motor cortex is suggested by electrophysiological findings; cortical spikes that precede myoclonic jerks using jerk‐locked back averaging . However, it is unclear whether the excitability remains after symptoms disappear.…”