Objective. Fibromyalgia (FM) in rheumatoid arthritis (RA) can cause consternation because symptoms are seen to be out of proportion to physician and laboratory assessments, and composite RA activity scores such as the 28 joint Disease Activity Score, Clinical Disease Activity Index, and Routine Assessment of Patient Index Data 3 (RAPID-3) can yield apparently "wrong" results. We explored the effect of polysymptomatic distress (PSD), a measure of fibromyalgianess and a quantity derived from the American College of Rheumatology 2010 FM diagnostic criteria, to explain the relationship of patient to physician variables.

Methods. We obtained PSD scores on 300 RA patients prior to ordinary clinical care, and assessed the associations of PSD with tender and swollen joints, physician global estimate of RA activity, pain, Health Assessment Questionnaire score, and composite RA activity measures during routine clinic assessments.

Results. PSD scores greater than the sample mean (8.8) were associated with increased patient symptoms regardless of the presence or absence of FM, while scores below the mean were associated with better patient outcomes. PSD scores predicted all patient outcomes and less strongly predicted physician outcomes. The discrepancy between patient and physician measures was greatest at low levels of physician-estimated disease activity.

Conclusion. PSD rather than FM diagnosis more usefully identifies and predicts disproportionate responses. Just as there are patients who lean disproportionately toward greater severity, there are also patients who disproportionately report milder symptoms. Composite measures used to assess RA are flawed, as they confound RA inflammation and patient distress, and more consideration should be given to disaggregated assessments. PSD also appears to be influenced weakly by RA disease activity.