The detection of calcium pyrophosphate crystals in the synovial fluid of patients with rheumatoid arthritis using the cytospin technique: prevalence and clinical correlation

There are only a few studies dealing with the detection and clinical impact of calcium pyrophosphate (CPPD) crystals in patients with rheumatoid arthritis (RA) published to date. In particular, data determined by the cytospin technique, which is an effective tool to enhance the crystal detection rate, are lacking. The objectives of this study were to determine the prevalence of CPPD crystals in the synovial fluid (SF) of patients with RA and to investigate whether the detection of CPPD crystals is correlated with demographic, clinical and serological features. We examined 113 consecutive SF samples of patients with RA, obtained from therapeutic arthrocentesis of knee joints. After cytocentrifugation, the sediments were examined by polarized microscopy for the occurrence of CPPD crystals. Demographic, clinical and serological data, acquired from the medical records, were compared between crystal-positive and crystal-negative subjects. CPPD crystals were observed in 20 of the 113 cases, representing 17.7 %. CPPD-positive and CPPD-negative subjects did not differ significantly in sex, duration of disease, Steinbrocker radiologic stage, disease activity score 28, as well as serum rheumatoid factor and anti-CCP positivity. Patients positively tested for CPPD crystals had a significantly higher age than CPPD-negative patients (p < 0.0001). An age-independent association of long-time treatment with diuretics and CPPD crystal formation was not found. In conclusion, demographic, clinical and serological characteristics of patients with RA were not associated with the occurrence of CPPD crystals. Age was the only significant influencing factor on CPPD crystal formation in patients with RA.