A 83 year old man presents to the clinic with progressive pain and swelling of the left knee for 8 months. He has a history of well controlled type 2 diabetes for 15 years. He doesn’t smoke or take any recreational drugs. He drinks alcohol socially. His surgical and family histories are unremarkable. Physical examination reveals a medial parapatellar hard movable mass and limited movement of the left knee. Excisional biopsy of the mass reveals glossy white calcified deposits which show positive birefringence under polarized light. What is the most likely diagnosis? A- Gout B- Pseudogout C- Osteoarthritis D- Acute arthritis E- Osteosarcoma Answer: http://medical-usmle.com/repeated-usmle-questions-85
