Objective: To characterize patients with both monosodium urate (MSU) and calcium pyrophosphate (CPP) crystals in their synovial fluid (SF).
Method: Forty-nine gout patients with acute arthritis were included. Those patients with MSU crystals only in their SF were compared to those patients with both MSU and CPP crystals in their SF.
Results: A total of 36 out of 49 patients (73.5%) had only MSU crystals, whereas 13 out of 49 (26.5%) had both MSU and CPP crystals in their SF. Co-deposition of CPP crystals was associated with long-standing gout disease (p = 0.022), kidney dysfunction (p = 0.024), and erosive arthritis (p = 0.049), but not with age.
Conclusion: Long-standing gout may be a risk factor for CPP deposition disease, and the frequency of CPP co-deposition may be higher than expected.