Acute Calcium Pyrophosphate Crystal Arthritis Flare Rate and Risk Factors for Recurrence.

OBJECTIVE: Little is known about acute calcium pyrophosphate (CPP) crystal arthritis flare rates and risk factors for recurrence. We characterized flares and determined the rate and predictors of acute CPP crystal arthritis flares in an academic medical center cohort. METHODS: We performed a retrospective cohort study among a random sample of patients with acute CPP crystal arthritis identified in the Partners HealthCare electronic medical record, 1991-2017. Flare was defined as self-limited, acute-onset synovitis with synovial fluid CPP crystals and/or chondrocalcinosis, not better explained by another cause. We calculated incidence rates (IR) for acute CPP crystal arthritis flare among all subjects and by sex. We estimated HR for recurrent flare using univariate Cox models that accounted for within-person correlated data. RESULTS: We identified 70 patients with acute CPP crystal arthritis with a total of 111 flares. Recurrent flares occurred in 24% of patients; half of flares occurred in a previously unaffected joint. The acute CPP crystal arthritis flare rate was 11.4 per 100 person-years overall (95% CI 8.2-15.4), 14.2 in women (95% CI 9.6-0.1), and 7.1 in men (95% CI 3.4-13.0). Cancer (HR 2.98, 95% CI 1.33-6.68) and chronic kidney disease (HR 2.92, 95% CI 1.10-7.76) were associated with a higher rate for recurrent flare. CONCLUSION: Recurrent flares occurred in about one-fourth of patients with acute CPP crystal arthritis and often occurred in previously unaffected joints. The acute CPP crystal arthritis flare rate was twice as high in women as in men.