Worm-Smeitink, M, Gielissen, M, Bloot, L et al. · Journal of psychosomatic research · 2017 · DOI
This study tested a questionnaire called the Checklist Individual Strength (CIS) that measures different types of fatigue, including how tired people feel, difficulty concentrating, lack of motivation, and reduced activity levels. Researchers gave this questionnaire to nearly 2,300 healthy people and over 5,000 patients with chronic fatigue to see if it accurately identifies severe fatigue. They found the CIS works well for measuring fatigue and recommended adjusting the score that indicates 'severe fatigue' from 35 to 40 points for ME/CFS research.
The CIS is widely used in ME/CFS clinical practice and research to measure fatigue severity and monitor treatment response. This study provides evidence that the CIS is a reliable, valid tool for assessing fatigue and establishes appropriate cut-off scores specific to ME/CFS populations, improving diagnostic accuracy and consistency across research studies.
This study validates a fatigue measurement tool but does not identify causes of ME/CFS fatigue, explain mechanisms underlying different fatigue dimensions, or determine whether fatigue severity scores predict outcomes or treatment response. The study is cross-sectional, so it cannot establish how fatigue changes over time or what factors drive disease progression.
About the PEM badge: “PEM required” means post-exertional malaise was an explicit required diagnostic criterion for participant inclusion in this study — not that PEM was studied, observed, or discussed. Studies using criteria that do not require PEM (e.g. Fukuda, Oxford) are tagged “PEM not required”. How the atlas works →
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