Clinical classification of post anoxic myoclonic status

Despite decades of research into the prognostic significance of post anoxic myoclonic status (MS), no consistent definition has been used to describe its clinical appearance. We set out to characterize the clinical features of MS and hypothesized that there are distinct clinical subtypes that may have prognostic implications.

Video EEG reports from 2008 to 2016 were searched to identify adult patients with post anoxic MS defined as persistent myoclonus for >30min beginning within 3days of cardiac arrest in a comatose patient. Forty-three patients met inclusion and exclusion criteria. To generate definitions of the clinical features of MS, we reviewed videos of 23 cases and characterized 3 distinct clinical semiologies. An additional 20 cases were independently reviewed and categorized by 3 raters to evaluate inter-rater agreement (IRA). All 43 patients were assigned to a group based on consensus review for the first 23 patients and majority agreement for IRA patients. We also examined the relationship between semiology and outcome.

Three distinct clinical semiologies of MS were identified: Type 1: distal, asynchronous, variable; type 2: axial or axial and distal, asynchronous, variable; and type 3: axial, synchronous, stereotyped. For IRA, Gwet's kappa was 0.64 indicating substantial agreement. Two of 3 type 1 patients (66.6%) and 7.4% of type 2 followed commands whereas none of type 3 followed commands (p=0.03).

We defined and validated a classification system of post anoxic MS based on clinical semiology. This classification may be a useful bedside prognostication tool.