When a pet scan is done for multiple myeloma, is it to look at the solid lesions or a full body scan to look at bone marrow?

Both: A pet scan usually is done with either a ct or MRI to create a 3-d image that evaluates the amount of active tracer seen in either the organs or bones- if a person has mm- it can efficiently detect activity in the bone marrow and can help guide treatment. There have been many studies done to determine how useful pet is in mm and it has overall been found very beneficial.

Look at bone lesions: A pet scan would not be done to look at bone marrow. That is done most likely with an aspirate smear to detect plasma cells in the marrow. The bone lesions are lytic or punched out and are accompanied by osteoblastic response. This means that radiographs or x rays are more useful than a pet scan or a bone scan. So get x ray(s) to check out these lesions.

Both: A pet/ct scan looks at all parts of the body, from the skull top the feet, if appropriate. If there is abnormally increased (or decreased) glucose metabolism, it will be seen - in bone marrow or lymph nodes, lungs or solid organs. For multiple myeloma, since bone lesions are more likely, even more attention is paid to the bones and marrow. But, the rest of the body is also examined carefully.