<prompt> An elderly male presents with headache, recurrent infections and multiple punched out lytic lesions of x-ray skull. Which of the following investigation will best help in establishing the diagnosis?Serum calciumProtein ElectrophoresisAcid phosphatase levelsAlkaline phosphatase levels  <response>: Patients presenting with symptoms such as headache, recurrent infections and multiple punched out lytic lesion on the skull suggest a diagnosis of Multiple Myeloma. It can be diagnosed by performing protein electrophoresis which shows a characteristic monoclonal spike visible in the beta or gamma globulin region. Ref: Current Medical Diagnosis and Treatment, 2012, Chapter 13 