Differences of opinion on systemic exercise intolerance disease are not 'mistakes': a rejoinder to Jason Sunnquist, Gleason and Fox

Differences of opinion about how case definitions are operationalized should not be characterized as 'mistaken.' Despite limitations, our study provides insight into how systemic exertion intolerance disease (SEID) criteria perform early in the course of myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) compared to other case definitions. To facilitate early, accurate diagnosis, research needs to be performed, ideally, prospectively with subjects who have not been ill for years. In addition, results of past treatment studies may not be applicable to many ME/CFS patients because criteria used for research differed from patients' clinical presentations. To avoid this potential mismatch between research employing the new clinically-focused SEID criteria should be promoted, rather than discouraged.