To investigate the neurophysiology of acute post-anoxic myoclonus and to localize the putative generator.

 Post-anoxic myoclonus(PAM) is a common complication of diffuse cerebral ischemia following cardiac arrest.Using a novel EEG-sEMG approach, we conducted a polygraphic neurophysiological analysis of acute PAM.

A cardiac arrest protocol was developed at our institution from 2022 to 2024. This included standard 18-channel scalp EEG placed according to the 10-20 international system. In addition, we placed sEMG electrodes over the masseter(CN V), orbicularis oris(CN VII), sternocleidomastoid(CN XI), and biceps brachii(C5,6). Each muscle was covered by two electrodes separated by 1-1.5 inches with a recording sampling rate of 200Hz via the Neurofax-1200 system by Nihon Kohden (Japan). A descending myogenic activation pattern (V → VII → XI → C6) was hypothesized to indicate a cortical origin, while a non-sequential pattern would suggest a reticular origin. To minimize bias, two independent researchers analyzed EEG and sEMG data separately. Each patient’s classification was determined based on the predominant pattern observed across 50 myoclonic discharges.

A total of 14 patients were analyzed. EEG and EMG findings were concordant in 9 cases, classifying them as either cortical (4) or reticular (5) myoclonus. The predominant EEG pattern in cortical myoclonus patients was a generalized burst-suppression pattern, with the bursts time-locked and preceding the myoclonus. One patient had a generalized periodic pattern. In 3 out of 5 reticular cases, the EEG showed a generalized background suppression. In 2 cases, there was a burst-suppression pattern, but the bursts were not time-locked to the myoclonus. In 5 cases, discrepancies between EEG and EMG classifications led to their designation as a mixed group.

Our preliminary findings indicate a feasible and technically easy EEG-sEMG protocol to monitor patients with acute PAM for appropriate classification of the myoclonus. The relationship to overall patient outcomes remains to be studied.