Gout and coexisting pseudogout in the knee joint.

Purpose: We report the unusual case of a 63-year-old man with gout and coexisting pseudogout (calcium pyrophosphate dihydrate crystal deposition disease) affecting the same joint. In this report, we describe the clinical features of the patient in addition to the characteristics of the crystals extracted from his affected joint, examined using compensated polarized microscopy.
Methods: Synovial fluid and specimens of the lateral meniscus of the patient's knee joint taken during arthroscopy were analyzed using compensated polarized microscopy to evaluate the presence and type of crystals.
Results: Compensated polarized microscopy revealed both monosodium urate (MSU) and calcium pyrophosphate dihydrate (CPPD) crystals extracted from the knee joint.
Conclusions: Our findings suggest that the coexistence of gout and pseudogout should be considered in the diagnosis of crystal-induced arthritis. Careful crystal evaluation using compensated polarized microscopy may reveal similar cases with MSU and CPPD crystals in the same joint.