Mixed monosodium urate and calcium pyrophosphate crystal-induced arthropathy. A review of seventeen cases

Among 4620 synovial fluid specimens examined in our laboratory from 1989 through 1992, 18.3% contained crystals (calcium pyrophosphate dihydrate, 55.7%; monosodium urate, 42%). Both calcium pyrophosphate dihydrate and monosodium urate crystals were found in 17 patients, usually in specimens obtained from the knee. Only five of these 17 patients had a known history of gout. Among the patients with a mixed crystal composition, the females had a higher mean age (78.5 years) than the males (53.2 years), in keeping with the fact that gout is exceedingly rare in premenopausal women. The two youngest men (40 and 45 years) had a history of meniscectomy, which is a known risk factor for early chondrocalcinosis.