AB0256 Differential diagnosis of seronegative ra: calcium pyrophosphate dihydrate deposition disease

Background Calcium pyrophosphate deposition (CPPD) disease is caused by calcium pyrophosphate (CPP) crystals and seen mainly in elderly. Clinical presentation can be heterogeneous. The arthropathy of CPPD may mimic RA, particularly if involving common joints seen in RA. Diagnosis of CPPD arthritis is based on CPP crystals seen in synovial fluid (SF) analysis, chondrocalcinosis (CC) seen in radiographs and/or on typical clinical presentation for CPPD. Early diagnosis of CPPD can be challenging and a proportion of CPPD patients may be misdiagnosed. We demonstrate 17 cases with CPPD initially diagnosed and treated as seronegative RA. Objectives To increase awareness that CPPD disease may resemble seronegative RA and to characterise clinical and radiographic phenotypes of these CPPD patients. Methods Altogether 435 early seronegative early RA patients were clinically diagnosed in a single rheumatology centre and scheduled for 10 year follow-up. All clinical data and radiographs were collected and reviewed. Patients were re-diagnosed as CPPD related arthritis if they had typical radiographic findings and suitable clinical pattern of CPPD or positive CPP crystal finding in SF. These patients are the subjects of this study. Results 17 patients were identified with a CPPD disease. The mean age at baseline was 71.2 years, and 82% were women. In 7 (41.2%) patients baseline symptoms were polyarticular, and in all these patients` wrist, MCP or PIP joints were affected; other symptomatic joints were hip (1 patient) and ankle (3 patients). The initial symptoms of 6 (35.3%) patients were oligoarticular, including MCP and PIP joint involvement (2 patients) or wrist and MCP, PIP or MTP joint symptoms (4 patients). Four (23.5%) patients were diagnosed as monoarthritis including ankle (1 patient) and wrist (3 patients). Seven patients (41.2%) fulfilled 1987 ACR criteria for RA and the diagnosis of early RA of the other 10 patients (58.8%) was based on clinical judgement. During the follow up period the SF analysis of 4 patients was available, 3 SFs showing positivity for CPP crystals. In 13 patients, SF had not been taken. In retrospect the baseline radiographs of 10 patients showed evidence of CC, either in wrists or knees. During follow up all patients developed typical clinical pattern for CPPD disease: chronic CPP crystal inflammatory arthritis (9 patients), acute CPP crystal arthritis (6 patients) and OA with CPPD (2 patients). All developed similar radiographic findings compatible with CPPD, including CC of triangular fibrocartilage (17 patients), CC of knee (9 patients), CC or narrowing of MCP joints (7 patients), CC of metatarsophalangeal (MTP) joints (4 patients), CC of symphysis pubis (1 patient), CC of glenohumeral joint (1 patient) and SLAC (5 patients). None of these patients developed typical RA-like erosions. Conclusions The prevalence of CPPD patients in our early seronegative RA patients was 3.9%. CPPD disease can mimic seronegative RA at baseline and is important in the differential diagnosis of seronegative arthritis. Reference [1] Zhang W, Doherty M, Bardin T, et al. European league against rheumatism recommendations for calcium pyrophosphate deposition. Part I: Terminology and diagnosis. Ann Rheum Dis. 2011;70(4):563–570. Disclosure of Interest None declared