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

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.