Diagnostic dilemma in a case of osteolytic lesions

A middle-aged male patient presented with fever, polyarthralgia, polyuria, easy fatigability and weight loss for 1 month. Clinically, there was only significant pallor and a swelling over the right sternoclavicular joint. On investigation, there was anaemia, raised urea, creatinine and pus cells in urine with growth of Escherichia coli. There were also hypercalcaemia and osteolytic lesions over the ribs, scapula, clavicle and skull along with distorted renal corticomedullary differentiation. Although the initial diagnosis was likely to be a case of multiple myeloma, serum protein electrophoresis was negative for the monoclonal band and no Bence-Jones protein was detected in urine. Bone marrow plasma cells were less than 10%, but the serum-free light chain assay revealed altered κ:λ ratio. Later in the course of the disease, a cervical lymph node appeared. The biopsy and immunohistochemistry of this lymph node revealed a CD5 positive diffuse large B-cell lymphoma, but unfortunately the patient succumbed to his illness after receiving the first cycle of Rituximab-Cyclophosphamide-Hydroxydoxorubicin-Oncovin-Prednisolone.