Post-hypoxic Myoclonus: Current Concepts, Neurophysiology, and Treatment

Abstract

Background: Myoclonus may occur after hypoxia. In 1963, Lance and Adams described persistent myoclonus with other features after hypoxia. However, myoclonus occurring immediately after hypoxia may demonstrate different syndromic features from classic Lance-Adams syndrome (LAS). The aim of this review is to provide up-to-date information about the spectrum of myoclonus occurring after hypoxia with emphasis on neurophysiological features.

Methods: A literature search was performed on PubMed database from 1960 to 2015. The following search terms were used: "myoclonus," "post anoxic myoclonus," "post hypoxic myoclonus," and "Lance Adams syndrome." The articles describing clinical features, neurophysiology, management, and prognosis of post-hypoxic myoclonus cases were included for review.

Results: Several reports in the literature were separated clinically into "acute post-hypoxic myoclonus," which occurred within hours of severe hypoxia, and "chronic post-hypoxic myoclonus," which occurred with some recovery of mental status as the LAS. Acute post-hypoxic myoclonus was generalized in the setting of coma. Chronic post-hypoxic myoclonus presented as multifocal cortical action myoclonus that was significantly disabling. There was overlap of neurophysiological findings for these two syndromes but also different features. Treatment options for these two distinct clinical-neurophysiologic post-hypoxic myoclonus syndromes were approached differently.

Discussion: The review of clinical and neurophysiological findings suggests that myoclonus after hypoxia manifests in one or a combination of distinct syndromes: acute and/or chronic myoclonus. The mechanism of post-hypoxic myoclonus may arise either from cortical and/or subcortical structures. More research is needed to clarify mechanisms and treatment of post-hypoxic myoclonus.

Keywords: Lance–Adams syndrome; myoclonus; neurophysiology; post-anoxic myoclonus; post-hypoxic myoclonus.

Figure 1. Neurophysiological findings in acute PHM. More than one pattern of electroencephalography was seen in the same patient during the course of myoclonus. Burst suppression was the most common pattern while alpha coma was the least common pattern observed. The highest rate of survival was seen in the diffuse slowing group and the lowest rate was seen in the spike-wave group. Multiple studies were commonly performed in the same patient.

Figure 2. Neurophysiological findings in CHRONIC PHM (LAS). Electroencephalography is the most common neurophysiological study followed by jerk-locked back averaging in chronic post-hypoxic myoclonus. An overwhelming majority of myoclonus in chronic PHM was found to be of cortical origin with jerk-locked back averaging. Multiple studies were commonly performed in the same patient.