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).
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.
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.
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.