A patient with pain in back. Lab investigation shows elevated ESR. X-ray skull shows multiple punched out lytic lesions. Most imp. Investigation to be done is -: (A) Serum acid phosphatase, (B) CT head with contrast, (C) Whole body scan, (D) Serum electrophoresis
Answer is D. This patient has : -

Multiple punched-out lytic lesions of the skull.
Elevated ESR
Back pain
Diagnosis is multiple myeloma.
Multiple myelomas is diagnosed by M bands on serum electrophoresis.