Fever of unknown origin (FUO) and a renal mass: renal cell carcinoma, renal tuberculosis, renal malakoplakia, or xanthogranulomatous pyelonephritis?

Often patients with fevers of unknown origin (FUOs) present with loss of appetite, weight loss, and night sweats, without localizing signs. Some are found to have a renal mass during diagnostic evaluation. In patients with FUOs and a renal mass, the differential diagnosis includes renal tuberculosis, renal cell carcinoma (hypernephroma), renal malakoplakia, and xanthogranulomatous pyelonephritis. A 68-year-old woman presented with an FUO during her diagnostic workup. She manifested an irregularly enlarged kidney on abdominal computed tomography (CT) scan, as well as a highly elevated erythrocyte sedimentation rate of more than 100 mm/hour, an elevated serum ferritin level, and chronic thrombocytosis, which favored a diagnosis of renal cell carcinoma. Renal malakoplakia and renal tuberculosis comprised further differential diagnostic considerations. Microscopic hematuria may be present with any of the disorders in the differential diagnosis, but was absent in this case. An abdominal CT scan was suggestive of xanthogranulomatous pyelonephritis. Because of concerns regarding renal cell carcinoma, the patient received a nephrectomy. The pathologic diagnosis was of xanthogranulomatous pyelonephritis, without renal cell carcinoma.