J Rheumatol
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Polysymptomatic distress (PSD) is the underlying metric of fibromyalgia (FM), and levels of PSD can identify criteria-positive FM with > 90% accuracy. We used levels of the PSD scale to test whether symptom levels in primary FM (PFM) and secondary FM (SFM) were the same and whether symptoms were equivalent in persons not meeting FM criteria. ⋯ PFM and SFM are equivalent regarding symptom burden. PSD scores are more informative about severity and severity within diagnosis than dichotomization into FM/non-FM. Studies of FM versus "healthy individuals," or FM versus other diseases, are inherently defective, while studies of FM and PSD in RA offer the opportunity to have meaningful comparison groups, because there are no readily available unbiased appropriate controls for PFM.