Imaging techniques in the diagnosis of dialysis-related amyloidosis

beta (2)-microglobulin amyloidosis (A beta M-2) is a major determinant of morbidity in patients on dialysis treatment. Symptoms of A beta M-2 amyloid are mainly related to (peri-)articular amyloid deposition. Imaging techniques [i.e., joint ultrasonography, X-ray, computed tomography (CT), or magnetic resonance imaging (MRI) findings], as well as conventional bone scans, are helpful in the screening of local lesions but are relatively nonspecific and/or not sensitive enough. Scintigraphic techniques using radiolabeled serum amyloid P component (SAP) or the radiolabeled A beta M-2 precursor protein, beta M-2, generate more specific results. A beta M-2 deposits have been visualized in several long-term hemodialysis patients by using I-123-labeled SAP. However, this scan did not show tracer accumulation in some frequently involved sites such as hips or shoulders, and frequently labeled the spleen, which is usually spared from A beta M-2 deposits. Improvements in technical sensitivity and specificity could be achieved by scanning with I-131-labeled beta M-2: this technique detected tracer accumulations corresponding to the typical distribution pattern of A beta M-2. Further, both the radiation exposure and the optical resolution of this latter scan have been refined by substituting In-111 for I-131. In a final step we generated recombinant human beta M-2 (rh beta M-2). While In-111 rh beta M-2 again failed to show significant tracer accumulation over joint regions in patients on short-term hemodialysis without evidence of A beta M-2, local tracer accumulations similar to those observed with natural, In-111-labeled beta M-2 could be demonstrated in long-term hemodialysis patients with evidence of A beta M-2. In conclusion, scintigraphy for A beta M-2 with In-111-labeled rh beta M-2 provides a homogeneous and safe recombinant protein source and represents a suitable detection method of beta M-2 amyloid deposits in dialysis patients.