Male patient, 36 years old, referring severe low back pain and refractory to painkillers for 3 months, associated to painful irradiation to the posterolateral region of the right tight. Reports unintentional weight loss of 7kg for the last 4 months. Laboratory tests: hemoglobin: 9.5g/dL; serum creatinine: 3.2mg/dL; total calcium: 14.7mg/dL; ionized calcium: 8.5mg/dL; phosphorus 4.7mg/dL and serum protein electrophoresis: monoclonal proteins of 2.82g/dL and 43.9% β-2 globulin fraction.