A 79-year-old man was admitted to the hospital complaining of fever for the past two weeks and cold shivers for the past one day. His medical history included multiple myeloma for which he was treated at that time with melphalan, prednisolone and bortezomib, as fourth line chemotherapy. According to the patient, he had no localizing complaints that indicate a focus of infection. Standard clinical evaluation did not reveal a site of infection. Laboratory results showed elevated inflammation parameters (C-reactive protein 186 mg/l) and a cytopenia (haemoglobin 7.8 gl/dl, mean corpuscular volume 9 9 fl, leukocyte count 4.2 x109/l, thrombocyte count 148 x109/l). Blood cultures, virus serology (Epstein-Barr virus, cytomegalovirus and herpes simplex virus) and imaging with computed tomorography, positron emission tomography-computed tomography and echocardiography revealed no focus of infection. Fever and cold shivers persisted despite broad spectrum antibiotics. Since the pancytopenia worsened despite a decrease of the Immunoglobin A lambda paraprotein level, a bone marrow puncture was performed.