A 63-year-old man develops pain and swelling in his knee. It appears warm, red, and swollen with decreased range of movement. A diagnostic aspiration is performed. Which of the following will most likely distinguish pseudogout from gout?
positive birefringent crystals
acute onset
involvement of single joints
involvement of large joints
Pseudogout (calcium pyrophosphate crystals - CPPD) is distinguishable from gout by positive birefringent crystals. CPPD are short, blunt rhomboids, and urate crystals (seen in gout) are needle-shaped with negative birefringence.
Immunology and Rheumatology