Diagnostics

ME/CFS diagnosis has historically been complicated by inconsistent and sometimes conflicting case definitions. The Fukuda 1994 criteria, Oxford criteria, Canadian Consensus Criteria (CCC), International Consensus Criteria (ICC), and IOM/SEID 2015 criteria differ substantially in their requirements — particularly regarding post-exertional malaise, which is required by CCC, ICC, and IOM but not by Fukuda or Oxford. Research increasingly demonstrates that case definition quality shapes research findings, with studies using strict PEM-required criteria identifying a more homogeneous patient population and more consistent biomedical findings. The atlas classifies each study by the case definition used.