UKMLA PLAB AMC USMLE Prometric MCQ

Correct answer: D

This patient presents with acute monoarthritis of the right knee. The clinical picture and the radiological findings are suggestive of pseudogout and calcium pyrophosphate deposition (CPPD), which is characterised by the presence of positively birefringent crystals on synovial fluid analysis (negatively birefringent ones are found in gout). The knee is the most common site affected by this disorder. Other locations include:  the triangular fibrocartilage of the wrist  sacroiliac joints  symphysis pubis  the glenoid of the shoulder  the labrum of the hip  the elbow  the ankle  acromioclavicular joint. CPPD is associated with hemochromatosis, primary hyperparathyroidism, hypothyroidism, and hypomagnesemia. Other findings include joint space narrowing, large subchondral cysts and many intra-articular bodies from subchondral bone fragmentation.