Combined Gout and Pseudogout Demonstrate Unique Clinicopathologic Features Compared to Those With Only Gout.

Although monosodium urate and calcium pyrophosphate dihydrate (CPPD) crystals have been documented together in synovial fluid, there are no descriptions regarding their simultaneous histologic presence within the same tophi. Furthermore, the incidence, significance, and clinicopathologic features of such patients have not been analyzed. We retrospectively reviewed consecutive cases of pathologic specimens over an ~4-year period with a confirmed histologic diagnosis of "gout" or "gouty tophi", focusing on concomitantly documented CPPD. A total of 159 gout cases involved 156 patients, including 127 males and 29 females (ratio 4.4:1), with ages ranging from 14 to 99 years (median 67). Nine (5.7%) patients (6 males; 3 females; ratio 2:1; age range 49 to 91 years, median 74) had evidence of both gout and CPPD crystals within the same tophaceous deposits. Concomitant gout/CPPD were more commonly associated with the upper extremities (5 [3, hands; 2, elbows]) than lower extremities (4, feet). Seven patients had a prior history of gout and 1 CPPD. The 150 cases from 147 patients of gout alone occurred in 121 males and 26 females (ratio 4.7:1), with ages ranging from 14 to 99 years (median 67). Gout alone was far more common in the lower extremities (109 cases) than the upper extremities (41). For combined gout/pseudogout, deposits of CPPD were intimately associated with the gouty tophi, deposited in irregular, curvilinear to serpiginous aggregates onto a significantly higher volume of uric acid crystals but never observed away from the tophaceous deposits. Confirmation of the uric acid crystals required polarization of unstained sections. In conclusion, the presence of concomitant CPPD and gouty crystals in the same tophaceous deposits is infrequently observed in pathology specimens. Compared with gout only, preliminary data suggests that patients with combined gout/pseudogout tophi are more likely to be older, female, and exhibit upper extremity involvement. Most such patients also have a prior history of gout.