A 65-year-old male was admitted to Peking Union Medical College Hospital. The patient had intermittent fever for 2 months with a maximum body temperature of 39.3 ℃ and elevated serum creatinine levels for 1 week. He had no other suggestive symptoms or positive signs. Laboratory test results suggested acute kidney injury and a sharp elevation in serum lactic dehydrogenase levels. Abdominal enhanced computed tomography (CT) revealed multiple low-density lesions, and further biopsy pathology demonstrated chronic inflammation. Thereafter, positron emission tomography (PET)/CT showed abnormally elevated uptake value for the bones throughout the entire body, in addition to the liver and brain. Repeated bone marrow biopsy finally confirmed metastatic bone cancer, which possibly originated from the kidney according to immunohistochemical staining. In this rare case of fever of unknown origin, the primary lesion was a renal tumor with bone, liver, and brain metastases. Enhanced CT and PET/CT provided negative results, and the diagnosis was eventually confirmed by repeated bone marrow pathology.

A 65-year-old male was admitted to Peking Union Medical College Hospital. The patient had intermittent fever for 2 months with a maximum body temperature of 39.3 ℃ and elevated serum creatinine levels for 1 week. He had no other suggestive symptoms or positive signs. Laboratory test results suggested acute kidney injury and a sharp elevation in serum lactic dehydrogenase levels. Abdominal enhanced computed tomography (CT) revealed multiple low-density lesions, and further biopsy pathology demonstrated chronic inflammation. Thereafter, positron emission tomography (PET)/CT showed abnormally elevated uptake value for the bones throughout the entire body, in addition to the liver and brain. Repeated bone marrow biopsy finally confirmed metastatic bone cancer, which possibly originated from the kidney according to immunohistochemical staining. In this rare case of fever of unknown origin, the primary lesion was a renal tumor with bone, liver, and brain metastases. Enhanced CT and PET/CT provided negative results, and the diagnosis was eventually confirmed by repeated bone marrow pathology.