The interrelation between clinical presentation and neurophysiology of posthypoxic myoclonus

OBJECTIVE: Posthypoxic myoclonus (PHM) in the first few days after resuscitation can be divided clinically into generalized and focal (uni‐ and multifocal) subtypes. The former is associated with a subcortical origin and poor prognosis in patients with postanoxic encephalopathy (PAE), and the latter with a cortical origin and better prognosis. However, use of PHM as prognosticator in PAE is hampered by the modest objectivity in its clinical assessment. Therefore, we aimed to obtain the anatomical origin of PHM with use of neurophysiological investigations, and relate these to its clinical presentation. METHODS: This study included 20 patients (56 ± 18 y/o, 68% M, 2 survived, 1 excluded) with EEG‐EMG‐video recording. Three neurologists classified PHM into generalized or focal PHM. Anatomical origin (cortical/subcortical) was assessed with basic and advanced neurophysiology (Jerk‐Locked Back Averaging, coherence analysis). RESULTS: Clinically assessed origin of PHM did not match the result obtained with neurophysiology: cortical PHM was more likely present in generalized than in focal PHM. In addition, some cases demonstrated co‐occurrence of cortical and subcortical myoclonus. Patients that recovered from PAE had cortical myoclonus (1 generalized, 1 focal). INTERPRETATION: Hypoxic damage to variable cortical and subcortical areas in the brain may lead to mixed and varying clinical manifestations of myoclonus that differ of those patients with myoclonus generally encountered in the outpatient clinic. The current clinical classification of PHM is not adequately refined to play a pivotal role in guiding treatment decisions to withdraw care. Our neurophysiological characterization of PHM provides specific parameters to be used in designing future comprehensive studies addressing the potential role of PHM as prognosticator in PAE.