Multiple myeloma (MM), the second most common hematologic malignancy, is characterized by clonal proliferation of plasma cells. Imaging is important for differentiating MM from other monoclonal plasma cell diseases as well as for disease staging. In particular, bone imaging is a critical component in the management of MM, as skeletal complications affect almost all patients with MM and have a profound influence on both patient morbidity and mortality.
Conventional radiography has long been the standard imaging method because it is widely available and comparatively inexpensive, but it does have limitations. Osteolytic lesions can be detected only after the loss of at least 30% of trabecular bone, malignant and nonmalignant causes of bone loss cannot be differentiated, and response to therapy is unevaluable.
In 2014, the International Myeloma Working Group (IMWG) updated the criteria for diagnosing MM and established that 1 or more lytic lesion detected on computed tomography (CT), whole-body low-dose CT (WBLDCT), or positron emission tomography (PET)/CT (regardless of whether this lesion was seen on skeletal radiography) as well as detection of more than 1 unequivocal (5 mm or larger in size) focal bone marrow lesion on magnetic resonance imaging (MRI) fulfilled the criteria of a MM diagnosis. These updates were introduced once it became clear that newer imaging modalities had a better detection rate compared with the traditional skeletal survey; this accelerated the implementation of these imaging methods into routine clinical practice.
In a review article, Elena Zamagni, MD, PhD, of the University of Bologna in Italy, and colleagues discussed the indications for use, advantages, and applications of the main imaging strategies used in the management of MM and smoldering MM.
“Our core message is that imaging in MM is nowadays not only a tool to stage the disease and follow patients from the clinical point of view — such as evaluating pain, fractures, and complications — but also a prognostic tool and a compulsory tool to evaluate response to therapy,” said Dr Zamagni. “New functional imaging techniques are the gold standard for these last 2 goals.”
WBLDCT allows detection of osteolytic lesions in the whole skeleton. It has a high rate of accuracy and doesn’t require the use of contrast agents, and patients experience 2 to 3 times less radiation exposure from WBLDCT compared with standard CT. Studies have also shown that WBLDCT is superior to whole body xray (WBXR) in detecting osteolytic lesions, particularly in the spine and pelvis.
PET/CT, which typically uses 18F-fluorodeoxyglucose (FDG) as the radiopharmaceutical, is a double strategy that is able to identify bone destruction and lytic lesions as well as assess tumor burden and disease activity. PET/CT can be used during the diagnostic workup of MM; previous research has reported that PET/CT has a sensitivity and specificity for detecting bone lesions between 80% and 100%. The ability to combine functional imaging with PET plus morphological assessment with CT makes this technique the most effective for identifying extramedullary disease.
MRI is another valuable technique for detecting skeletal involvement in MM. It has the highest sensitivity for detecting bone marrow infiltration by myeloma cells and does not expose patients to radiation. Several studies have shown that both axial and whole body MRI have a higher sensitivity than WBXR for detecting bone involvement in MM. Studies comparing MRI with PET/CT have found the 2 modalities to be equally effective in detecting focal lesions.