Q- An 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 does not 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 and Explanation
Calcified deposits, which show positive birefringence under polarized light, are calcium pyrophosphate. This is a typical presentation of pseudogout.
Gout deposits show negative birefringence. Osteoarthritis, acute arthritis and osteosarcoma show different clinical pictures and biopsies.
The correct answer is B
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Pseudogout