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Background: Acute post-anoxic myoclonus (PAM) can be divided into an unfavorable (generalized/subcortical) and more favorable ((multi)focal/cortical) outcome group which could support prognostication in post-anoxic encephalopathy, however the interrater variability of clinically assessing these PAM subtypes is unknown.
Methods: We prospectively examined PAM patients using a standardized video protocol. Videos were rated by three neurologists who classified PAM phenotype (generalized/(multi)focal), stimulus sensitivity, localization (proximal/distal/both), and severity (Clinical Global Impression-Severity scale (CGI-S) and Unified Myoclonus Rating Scale (UMRS)).
Results: Poor interrater agreement was found for phenotype and stimulus sensitivity
(κ=-0.05), moderate agreement for localization (κ=0.46). Substantial agreement was obtained for the CGI-S (intraclass correlation coefficient (ICC)=0.64) and almost perfect agreement for the UMRS (ICC=0.82).
Discussion: Clinical assessment of PAM is not reproducible between physicians, and should therefore not be used for prognostication. PAM severity measured by the UMRS appears to be reliable, however the relation between PAM severity and outcome is unknown.

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