Working Diagnosis:
Given the presence of positively and negatively birefringent crystals on synovial fluid analysis, the patient was diagnosed with inflammatory arthritis secondary to both gout and CPPD.

Treatment:
Four milliliters of serosanguinous fluid was aspirated from the knee and sent for analysis. A corticosteroid injection was done simultaneously for pain relief. The patient was advised to ice, rest, and use NSAIDs as needed. Once results showed the presence of both gout and CPPD, he was instructed to take Colchicine in addition to the previous recommendations. Pain resolved with this treatment.

Outcome:
Activity was advised once pain and swelling subsided. However, his symptoms recurred 4 weeks after his Sports Medicine visit, and he had run out of Colchicine. He returned to the ED, and was treated with Toradol and Colchicine. His primary care physician also placed him on Allopurinol on follow up 2 days later with improvement in pain. He has not returned for follow up in Sports Medicine Clinic.

Author's Comments:
Gout and CPPD occurring simultaneously in the same joint is rare. One prior case study suggests this condition may be under diagnosed due to high technical difficulty in diagnosing CPPD under polarized light microscopy. This patient also did not have risk factors for CPPD such as hypercalcemia or loop diuretic use. It is important to recognize that Gout and CPPD can affect one joint concurrently, but the implications are unclear. Further studies should be done investigating whether having Gout increases the risk of developing CPPD, as well as if having both conditions simultaneously affects treatment course or relapse rate.

Editor's Comments:
Great case and well delineated. It is interesting that he had such an acute and mechanical presentation. Crystal athropathies can certainly cause severe pain and swelling, but he described such mechanical symptoms surrounding his patella, limited range of motion, and sense of locking/instability which is uncommon. Perhaps the instability could be related to pain inhibition of extensor mechanism, but it’s hard to use the gout/CPPD to explain his locking concerns. I would consider advanced imaging to rule out chondral injury or loose body. While his pain resolved after treatment with colchicine, he also had a steroid injection to the knee which certainly could hide chondral pain. While it seems a bit of a longshot, it certainly is known that presence of monosodium urate crystals can exist without symptoms (ref 1), and CPPD can be present in other causes of joint disease such as OA and RA.

References:
Bardin T, Richette P. Definition of hyperuricemia and gouty conditions. Curr Opin Rheumatol. 2014 Mar;26(2):186-91

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