[Value of magnetic resonance imaging in myeloma]

Magnetic resonance imagery (MRI) of the spinal cord has become a standard method and its diagnostic and prognostic power in multiple myeloma has been widely demonstrated. Before treatment, MRI reveals two basic types of abnormalities yielding focal and diffuse signals. Focal lesions are seen as localized hyposignals on spin echo T1 sequences (SET1) and are enhanced by injection of gadolinium and changed to hypersignals in T2 weighted sequences. These images identify nodular tumoural masses. Diffuse lesions are seen most often as homogeneous SET1 images with an intensity similar to the vertebral body. This type of image is not specific of tumoural infiltration and can be benign in nature. The second type of diffuse signal is often called a "salt and pepper" image due to the juxtaposition of multiple hyposignals (suspected tumoural tissue) and hypersignals (fat tissue). We have observed this type of image in 27% of our series of multiple myelomas. The capacity of MRI to detect myelomas located in bone tissue is much greater than conventional radiography of the spine and is particularly sensitive to expansive tumoural lesions threatening the cord. MRI should always be performed as part of the initial work-up even in the absence of clinical signs. There is a good correlation between MRI of focal tumours and the biological response to treatment, although other biological markers may be more precise and easier to obtain. MRI can also be used to differentiate between benign monoclonal gammapathy and multiple myeloma, particularly in cases where there is a disagreement between the clinical and laboratory data. We have also studied MRI in solitary plasmacytomas of the spine.