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 -
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.
Serum acid phosphatase
CT head with contrast
Whole body scan
Serum electrophoresis