The 2010 ACR-EULAR Classification Criteria for RA leaves a lot of "wiggle room" as "joint involvement" refers to any swollen OR TENDER joint on examination with exclusion of the DIP joints, thumb and 1st toe. Although this definition is for definite clinical synovitis not better explained by another diesase (fibromyalgia?), I have a lot of fibro patients who have "joint involvement" by this criteria. The additional diagnostic burden of SpA (nr-axial or peripheral) only aggravates this fuzzy definition of an involved joint as joint tenderness is a surrogate for inflammatory joint swelling. I suspect that over-diagnosis of RA based on this classification criteria confounds clinical reports regarding treatment efficacy and results in over-treatment with immunosuppressive medications.