Prevalence of calcium pyrophosphate deposition disease in a cohort of patients diagnosed with seronegative rheumatoid arthritis.

OBJECTIVES: We aimed to characterise the clinical and radiographical phenotype of calcium pyrophosphate dihydrate deposition (CPPD) disease in patients initially diagnosed with seronegative RA, and to increase the awareness that CPPD disease can be falsely diagnosed as seronegative rheumatoid arthritis (RA). METHODS: Altogether 435 early seronegative RA patients were clinically diagnosed in a single rheumatology centre and scheduled for a 10-year follow-up. All clinical data were collected and reviewed. CPPD-related arthritis was suspected if a patient had typical radiographical findings and suitable clinical pattern of CPPD or calcium pyrophosphate crystals were found in the synovial fluid. These patients are the subjects of this study. RESULTS: Among 435 seronegative RA patients, 17 patients (3.9%) (baseline mean age 71.2 years, 82% women) with CPPD disease were identified. CPPD resembling clinical patterns in these patients were: chronic CPP crystal inflammatory arthritis (9 patients), acute CPP crystal arthritis (6 patients) and OA with CPPD (2 patients). All had typical radiographical findings of CPPD: Chondrocalcinosis (CC) of triangular fibrocartilage (17 patients [100%]), CC of knee (9 patients [53%]), CC or narrowing of metacarpophalangeal joints (7 patients [41.2%]), CC of metatarsophalangeal joints (4 patients [23.5%]), CC of symphysis pubis (1 patient [5.8%]), CC of glenohumeral joint (1 patient [5.8%]) and scapholunate advanced collapse (5 patients [29.4%]). None of these patients developed typical RA-like erosions. CONCLUSIONS: CPPD disease can mimic seronegative RA at baseline and is important in the differential diagnosis of seronegative arthritis at baseline and during follow-up. The prevalence of CPPD patients in our early seronegative RA patients was 3.9%, the percentage was 7.0% among patients ≥60 years at baseline.

Does early seronegative arthritis develop into rheumatoid arthritis? A 10-year observational study.

OBJECTIVES: To investigate the 10-year clinical course of patients with seronegative arthritis with the emphasis of reclassification of diagnoses when applicable. METHODS: A total of 1030 patients including 435 seronegative cases were classified as early RA in 1997-2005 at Jyväskylä Rheumatology Centre and prospectively scheduled for a ten-year follow-up. Clinical data from the follow-up visits and the case-reports until and including the 10-year visit or death, whichever happened earlier, were retrospectively collected and reviewed with re-classification of the cases when applicable. Descriptive statistics were used. RESULTS: Among the 435 seronegative cases (69 % women, baseline mean age was 59 years), 13 (13/435 [3%]) could be reclassified as seropositive or erosive RA: 4 turned seropositive (2 for ACPA and 2 for RF [> 2x reference level]) and 9 developed erosions typical for RA. Reclassification revealed 68 (16%) cases of polymyalgia rheumatica, 46 (11%) psoriatic arthritis, 45 (10%) osteoarthritis, 38 (8.7%) spondyloarthritis, 15 (3.4%) plausible reactive arthritis, 10 (2.3%) gout, 17 (3.9%) pseudogout, 6 (1.4%) paraneoplastic arthritis, 6 (1.4%) juvenile arthritis, 2 (0.5%) haemochromatosis, 3 (0.7%) ankylosing spondylitis, 2 (0.5%) giant cell arteritis, and 8 miscellaneous diagnoses. The other 140 patients (32%) could not be reclassified in any clear-cut diagnosis and had features of transient arthritis (n=41), seronegative spondyloarthritis (n=47), while 49 remained unspecified. CONCLUSIONS: Over a 10-year follow-up period, reclassification revealed significant heterogeneity in the diagnosis of seronegative RA. Therefore, seronegative arthritis should not be studied as a homogenous entity.