Multidetector computed tomography (MDCT) has been used in the detection of osteolytic lesions in multiple myeloma because it allows for whole body imaging and excellent anatomic detail. Mahnken et al
. studied the utility of MDCT in 18 patients with Durie–Salmon stage III multiple myeloma and compared the findings with those of the skeletal survey [8
]. In the 18 patients, a total of 325 vertebrae were examined. Their findings showed that the skeletal survey detected bone lesions in 207 vertebrae, compared to 231 vertebral lesions detected by MDCT. Importantly, MDCT detected twice as many lesions at risk of fracture, compared to the skeletal survey (12 vs. 6), defined as lytic lesions with >50% volume loss.
A major disadvantage of MDCT, however, is high radiation doses (>35 mSv). An alternative approach is the use of low dose CT (LDCT) where the average dose is about 3.3 mSv. Gleeson and colleagues tested LDCT’s feasibility in diagnosing and staging patients with multiple myeloma [9
]. In their study, 34 patients with biopsy-confirmed multiple myeloma and five with monoclonal gammopathy of undetermined significance (MGUS) or smoldering multiple myeloma (SMM) were enrolled. All patients underwent LDCT and a skeletal survey. LDCT was found to detect more osteolytic lesions, allowing the restaging of 25 cases (20 cases were upstaged) using the Durie–Salmon PLUS staging system. One patient was also found to have a clinically important lesion in the vertebral body with erosion into the spinal canal, detected by LDCT but not the skeletal survey. This patient subsequently required urgent radiation therapy.
These two studies show that computed tomography (whether high dose or low dose) appears to be superior to the skeletal survey for the detection of osteolytic lesions. Detection of these additional lesions has the potential to alter clinical management.
Another area of great interest is the fusion of anatomic imaging (CT) with functional imaging (PET). Functional imaging using 18
F-FDG PET allows the detection of malignant plasma cells because 18
F-FDG is trapped in the cells after being taken up via GLUT1 glucose transporters, since it is not recognized by the hexose monophosphatases and therefore not further metabolized [10
]. When PET scan results are combined with imaging obtained from low dose CT (18
F-FDG PET/CT), the presence of osteolytic lesions, focal lesions in the bone marrow, and extramedullary disease can be detected [11
F-FDG PET/CT was compared to the skeletal survey, Nanni et al
. found a higher number of lesions in 16 out of 28 patients with newly diagnosed symptomatic myeloma [12
]. In nine of the 16 patients, the skeletal survey was completely normal, while 18
F-FDG PET/CT detected one or more lytic bone lesions. They also found that 18
F-FDG PET/CT detected a second bone lesion in a patient who was originally thought to have a solitary plasmacytoma, changing the diagnosis to multiple myeloma. Other studies have calculated a sensitivity range of 80–90% and a specificity range of 80–100% of 18
F-FDG PET/CT in detecting osteolytic lesions in multiple myeloma [13
Because of the lack of osteoblastic response to lytic lesions, bone scintigraphy has a limited role in the staging of patients with multiple myeloma. Its sensitivity in detecting multiple myeloma bone disease was found to range between 40 and 60% [15
]. When Ludwig et al
. compared bone scintigraphy to the skeletal survey in multiple myeloma, they found that radionuclide imaging was inferior to conventional X-rays in the detection of bone lesions [15
]. This is in contrast to 18
F-NaF PET/CT, which was found to be sensitive to both osteoblastic as well as osteolytic lesions [16
]. Increased 18
F-fluoride uptake was found at the periphery of these lytic lesions [16
]. When combined with LDCT, the specificity of 18
F-NaF PET increases, allowing it to distinguish benign lesions from malignant ones. Further studies are required to investigate the utility of 18
F-NaF PET/CT in the detection of myelomatous bone disease.