Diffuse large B-cell lymphoma masquerading as multiple myeloma.

We report a case of a woman in her 60s who initially presented with typical symptoms of multiple myeloma, including fatigue, muscle cramps, lower back pain, hypercalcaemia, renal impairment and anaemia. Laboratory testing revealed elevated free light chains and M protein bands. Treatment was initiated for a working diagnosis of multiple myeloma. However, bone marrow assessment did not find plasma cells, instead revealing that the malignant clonal cells were of B-cell origin. Treatment was subsequently changed to a chemotherapy regimen for diffuse large B-cell lymphoma. After a suboptimal response, the patient received further treatment with a new regimen, resulting in a good response with no signs of active disease. Over 1 year after completing treatment, the patient remains well.