DECT Imaging Unmasks MSU Crystals Despite Negative Aspiration

A 64-year-old man with a history of gout (unproven, on allopurinol 300 mg), heart failure (Ejection Fraction 25%–30%, on diuretics), and atrial fibrillation (on apixaban) presented with a 5-day history of pain and swelling in the right knee and ankle. Initially, he experienced a gout flare in both first metatarsophalangeal joints and the left ankle, which resolved with a 6-day prednisone taper. Subsequently, he developed swelling in the right knee and ankle, prompting emergency care. Examination revealed synovitis, and joint aspiration yielded 3 mL of serosanguineous fluid (RBC 222,933/μL, nucleated cells 268/μL), negative for monosodium urate crystals, and cultures. Laboratories showed CRP 214, creatinine 2.0, uric acid 8.4, and BUN 40. Knee x-ray films demonstrated prepatellar swelling, and DECT (dual-energy computed tomography) confirmed monosodium urate crystal deposition in the foot and ankle (Figure 1, A and B, indicated by white arrows) and in the knee (Figure 1; C, anterior view; D, lateral view; and E, posterior view), over joints, tendons, and ligaments. He was treated with anakinra, resulting in symptom resolution. Differential Diagnoses: Partially treated gout arthritis Septic arthritis Pseudogout Hemarthrosis FIGURE 1