Whole-body low-dose multidetector row-CT in the diagnosis of multiple myeloma: an alternative to conventional radiography
Introduction
Multiple myeloma (MM) is a malignancy of plasma cells showing variable degrees of differentiation [1]. Typically, it involves the bone marrow and is usually multicentric. Durie and Salmon [2] showed that lytic bone lesions, hemoglobin, serum calcium and the monoclonal component blood levels significantly correlate with tumor mass and patient eventual survival. Their staging system is the most widely used for untreated multiple myeloma patients, based on the size of the tumor mass and M-gradient (M-protein level), respectively. According to this classification system, the task of the radiologist is to bring roentgenographic evidence of typical punched-out lytic bone lesions in order to categorize the stage of multiple myeloma. Patients with more than two unequivocal lytic lesions are classified as stage III, for which immediate treatment is indicated [3]. The diagnosis must yet finally be confirmed by a bone marrow aspirate or biopsy [4]. Bone marrow infiltration exceeding a certain degree leads in most cases to typical imaging findings on conventional X-ray and CT, including osteolysis, osteopenia and seldom osteosclerosis (e.g. “ivory vertebra”) [5]. Bone lesions in the appendicular skeleton are mostly well recognized, both by conventional X-ray, and CT. Lesions of multiple myeloma involving the axial skeleton, the thoracic cage and the skull, however, are better recognized by CT because of lacking add-up effects of interposed, different radioopaque soft tissue and bony structures, as on planar conventional X-ray images, sometimes missing even centimeter-large lytic lesions. Thus, the superiority of CT over conventional X-ray diagnosis in imaging skeletal lesions is a methodical one and must not be questioned. One main impediment in replacing conventional X-ray staging by CT represents the much higher radiation exposure associated with standard CT, in comparison with conventional radiographs. The effective dose, following radiological diagnosis, plays in stage III multiple myeloma patients, admittedly, a subordinate role, because of reduced life expectancy. However, monoclonal gammopathy of unknown significance (MGUS) patients suspected of multiple myeloma should not be unnecessarily overexposed to radiation. Therefore, establishing a low-dose CT-protocol, with a radiation exposure in a range comparable to that of conventional roentgenography, could represent a superior alternative in the imaging approach of this disease.
The aim of this study was to establish an optimised whole-body low-dose multidetector row-CT (MDCT) investigation protocol for staging and follow up of multiple myeloma, able to replace whole-body conventional radiography, and also appropriately deliver supplementary data about unexpected findings outside the skeleton, for instance in the lung, abdominal or pelvic viscera.
Section snippets
Patients
Between September 2002 and April 2003, a number of 100 consecutive patients (67 male and 33 female) with a mean age of 63.5 years (range 50–81 years) with diagnosed multiple myeloma (n = 86), or MGUS (n = 14), were included in this prospective study. There were two major requests of the clinician to the CT: correct classification of the patient into one of the three classical MM-stages, according to Laroche, and diagnosis of extramedullary plasmacytoma. A whole-body low-dose MDCT was performed
Results
Seventy patients showed multiple osteolysis, five had solitary manifestations, whereas in 25 patients CT revealed no bone lesions. Twenty-eight patients had no prior therapy. Thirty-five (35%) (n = 10) of them showed reduced bone density, while the rest demonstrated normal bone density. From the group of patients with pre-therapy (chemotherapy, radiation or biphosphonate) only 21% (n = 15) showed reduced bone density.
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Axial image resolution was rated better or equal to MPR in all 100 cases. The
Discussion
Since the introduction of the multiple myeloma classification system by Durie and Salmon, conventional radiographs are considered state-of-the-art in the diagnosis of multiple myeloma bone lesions. It is, however, known that the whole-body radiographic survey is inadequate for depiction of small lytic bone lesions, particularly in the axial skeleton, and therefore, inaccurate for staging this patient category. Underestimation of bone lesions by conventional radiography could lead to
Conclusion
We recommend the implementation of low-dose whole-body multidetector-CT in the staging and monitoring of multiple myeloma patients, as a precise and quick diagnostic tool, with high acceptance among patients and medical personal, which also enables acquisition of precious, complementary data concerning other organs. On the basis of our data, we perform whole-body low-dose CT in thin patients using a tube current of 40 mAs, increasing the dose up to 60 mAs in overweighed patients, or patients with
Acknowledgements
We thank Mr. Markus Buchgeister from the Department of Medical Physics of the University of Tübingen for his support in establishing the radiation dose for all energy levels chosen, using an anthropomorphic Alderson Rando Phantom, as well as Mr. Klaus Herz from the Department for Radiation Protection of UKT for guiding in the calculation of the effective dose in the conventional radiological diagnosis.
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