Green pixels on DECT: Is it gout?

An 80-year-old man developed pain and swelling of both knees while hospitalized with an acute viral illness causing significant dehydration and hyponatremia. He denied having any prior history of gout however did have a brother with a diagnosis of gout. Large bilateral knee effusions were seen on physical exam without overlying redness or tophi present. Lab work was significant for elevated C- reactive protein at 190 mg/dL and uric acid below normal range at 3.3 mg/dL. His leukocyte count and renal function were unremarkable. A right knee x-ray showed mild osteoarthritis, chondrocalcinosis, and a large effusion. The primary hospital team ordered a dual-energy CT scan (DECT) of his knees which showed diffuse chondrocalcinosis (Panel A, arrow), monosodium urate (MSU) deposition in bilateral knees (Panel B, arrows), large joint effusions, and tricompartmental osteoarthritis (OA). Given findings of MSU deposition on DECT, rheumatology was consulted who performed aspiration of both knees and injected corticosteroids. Synovial fluid showed intracellular calcium pyrophosphate (CPP) crystals; MSU crystals were absent. Cultures were negative for infection. Given the synovial fluid findings, he was diagnosed with acute CPP crystal arthritis. The patient's knee pain subsided for several months. He subsequently had a flare of knee pain and swelling about 6 months later, which was again alleviated with triamcinolone injection in the clinic. He was offered prophylactic treatment with daily colchicine however he declined in favor of a wait and see approach.