Optimising fibromyalgia criteria: evidence from the UK Biobank

To evaluate the performance of the 2016 revisions to the modified fibromyalgia criteria (FM2016) in identifying individuals with self-reported fibromyalgia in a large population sample, and to test whether simplified symptom thresholds and alternative definitions of widespread pain improve case-finding utility.

We used data from 167,184 UK Biobank participants who completed an "Experience of Pain" online questionnaire. Logistic regression and clinical utility indices (CUI+ and CUI-) were used to assess the performance of the FM2016 criteria and alternative modifications in case-finding and screening self-reported fibromyalgia diagnoses. Cut-off combinations for the scales of the FM2016, the Widespread Pain Index (WPI), Symptom Severity Scale (SSS), and the Polysymptomatic Distress Scale (PSD) were iteratively optimised. We also compared different definitions of widespread pain, including a single self-reported item on "pain all over the body".

The FM2016 criteria showed high specificity (98·4 %) but low sensitivity (37·0 %) and case-finding utility (CUI+=0·111). A simplified set of criteria, WPI≥4, SSS≥4, and PSD≥12, conditional on self-reported chronic pain all over the body, improved case-finding utility (CUI+=0·163) while maintaining high screening ability (CUI-=0·974). Other definitions of widespread pain performed less well.

In this large population-based study, simplified criteria incorporating a single question on widespread pain and easier-to-apply symptom cut-offs performed marginally better in identifying those with a diagnosis of FM.