Anti-citrullinated protein antibodies are associated with osteopenia but not with pain at diagnosis of rheumatoid arthritis: data from the BARFOT cohort

BackgroundAnti-citrullinated protein antibodies (ACPA) have been suggested to have a potential role in both bone loss and pain in rheumatoid arthritis (RA), based on studies in vitro and in animal models. Here we addressed if anti-cyclic citrullinated (anti-CCP) antibodies were associated with osteopenia or pain in patients with RA, at the time for diagnosis.MethodsBaseline data from the BARFOT (Better Anti-Rheumatic PharmacOTherapy) cohort, which consists of patients with RA with a disease duration of 1year or less, were analyzed. To be included, they should have been assessed by anti-CCP, dual-energy X-ray absorptiometry (DEXA) of lumbar spine and hip, and/or digital X-ray radiogrammetry (DXR) of the metacarpal bones. Osteopenia was defined as a z-score <-1 SD. Pain VAS >40mm, was defined as patient unacceptable pain. Multiple logistic regression analyses were performed to assess whether anti-CCP was independently associated with osteopenia or unacceptable pain.ResultsOf the 657 patients, 65% were women, 58% were anti-CCP positive, 37% had osteopenia in the lumbar spine, and 29% had osteopenia in the hip. Sixty-one percent had unacceptable pain at diagnosis. Patients positive for anti-CCP had significantly more frequently osteopenia in the femoral neck and Ward's triangle compared with anti-CCP-negative patients (p=0.016 and 0.003, respectively). This difference was found in men at any anti-CCP titer, but in women, osteopenia in these hip locations was found only in those with high anti-CCP titers (>500IU/ml). Anti-CCP was not associated with osteopenia in the lumbar spine or the metacarpal bones. In multiple logistic regression analyses, anti-CCP was independently associated with osteopenia in the femoral neck and/or Ward's triangle but not with unacceptable pain. Instead, inflammatory variables were independently associated with unacceptable pain.ConclusionThese data show that in patients with early RA, anti-CCP positivity was independently associated with osteopenia in the femoral neck and/or Ward, but not in the lumbar spine. In our patients, we could not confirm a recently suggested association between anti-CCP antibodies and pain. Further studies are necessary to explore the possible clinical relevance of interactions between ACPA, bone, and pain found in vitro and in animal models.