Bone Marrow Gouty Tophi With Plasma Cell Myeloma

Dear Editor, Gout is a systemic disease characterized by recurrent, painful arthritis caused by the deposition of uric acid crystals [1]. Uric acid crystal deposition occurs in tissues when serum uric acid level rises above the normal threshold. The pathological threshold of uric acid for hyperuricemia is 0.40 mmol/L [2]. A deposit of uric acid crystals in patients with longstanding hyperuricemia is termed a tophus [3]. Gouty tophi generally occur at the first metatarsophalangeal joints, ears, and finger pulps; however, although rare, gouty tophi have also been reported at non-skeletal sites including the bronchi, mitral valve, liver, breasts, and even bone marrow (BM) [3-5]. To date, only two cases of gout involving the BM have been reported [4, 5], and neither of them was accompanied by other hematologic malignancies such as plasma cell myeloma (PCM). Therefore, we report the first case of gouty tophi in the BM of a patient with PCM. This study was approved by the Institutional Review Board of Soonchunhyang University Hospital, Seoul, Korea (IRB File No. 2019-04-002). A 67-year-old woman, who had been receiving dialysis for four yrs owing to monoclonal gammopathy of undetermined significance and end-stage renal disease, was admitted to the Soonchunhyang University Hospital, Seoul, for an evaluation of frequent catheter occlusion. She also complained of severe pain in the distal interphalangeal joints in both hands. The initial laboratory findings were as follows: hemoglobin, 94 g/L (reference range, 120-160 g/L); white blood cell count, 7.1×10/L (4.010.0×10/L); platelet count, 146×10/L (130-450×10/L); prothrombin time (PT), 9.9 seconds (9.3-11.6 seconds); activated partial thromboplastin time (aPTT), 32.0 seconds (27.8-41.7 seconds); fibrinogen, 2.95 g/L (2.09-3.77 g/L); D-dimer, 9,812 μg/L (0-243 μg/L); anti-thrombin, 26% (65-129%); protein C, 59% (70-148%); free protein S, 58.8% (69.4-138.3%); blood urea nitrogen (BUN), 17.11 mmol/L (2.14-7.14 mmol/L); serum creatinine, 431.40 μmol/L (44.20-106.08 μmol/L); uric acid, 0.30 mmol/L (0.14-0.42 mmol/L); total protein, 50 g/L (64-83 g/L); albumin, 16 g/L (35-52 g/L); IgG, 8.96 g/L (7.00-16.00 g/L); IgA, 1.81 g/L (0.70-4.00 g/L); IgM, 0.88 g/L (0.40-2.30 g/L); free light kappa chain, 0.13 g/L (0.03-0.19 g/L); free light lambda chain, 10.39 g/L (0.05-0.26 g/L); free light kappa chain/free light lambda chain ratio, 0.12 (0.26-1.65); and β2-microglobulin, 2,412.67 nmol/L (84.82-203.56 nmol/L). Serum protein electrophoresis revealed two monoclonal peaks in the gamma region and immunofixation electrophoresis confirmed the presence of double gammopathy, IgG-lambda. The level of monoclonal protein was 6.6 g/L. Eight days after admission, the uric acid level increased to 0.52 mmol/L. A BM aspirate smear showed that plasma cells accounted for 45.2% of all nucleated cells, and a BM section revealed focally infiltrated plasma cells with multiple uric acid crystals (gouty tophi) with foreign body reaction (Fig. 1). Immunophenotypic analysis revealed that the plasma cells were CD19-, CD56dim+, and CD45and showed cytoplasmic lambda light chain restriction (tumor burden: 31.5%). No apparent cytogenetic abnormalities were found by FISH for t(4;14)(p16;q32), t(14;16)(q32;q23),