Invasive tophaceous pseudogout in the temporomandibular joint: misdiagnosis as tumor: case report and review of the literature.

We report a case of focal calcium pyrophosphate dihydrate (CPPD) arthropathy in a 72-year-old, white woman that occurred in the temporomandibular joint (TMJ), a relatively unusual location for CPPD crystals. The patient underwent surgical exploration and radiation therapy because of histologic interpretation of an initial biopsy specimen as showing metastatic poorly differentiated carcinoma. Further evaluation of the specimen revealed the presence of positively birefringent crystals under compensated polarizing light microscopic examination. Previously reported cases of CPPD affecting the TMJ have also shown that this may mimic neoplastic or infectious conditions. Tophaceous pseudogout at the TMJ is a surprisingly common complication of CPPD deposition disease. As in our patient, it can occur without known CPPD at other sites.