Diagnostic aspects of β2-microglobulin amyloidosis

Osteoarticular symptoms and signs, such as carpal tunnel syndrome, periarthritis humeroscapul- aris, synovial and joint inflammation, lead to the clinical diagnosis of /?2-microglobulin (/?2-M) amyl- oidosis. Radiologically, destructive arthropathy, spondylarthropathy and periarticular cystic bone radiolucencies can be demonstrated by plain X-ray and conventional and computed tomography. Magnetic resonance is used to visualize amyloid masses in special locations such as the cervical spine. Joint ultrasonography demonstrating thickening of synoviae and tendons has become a useful non-invasive dia- gnostic tool, although it is not specific for /J 2-M amyloidosis, and results depend on observer experi- ence. Efforts to develop more specific methods for demonstration of amyloid deposits have led to two scintigraphic techniques based on the injection of radiolabelled proteins which are incorporated into the amyloid tissue. One method uses serum amyloid P component, a non-specific constituent of all types of amyloid. An alternative imaging technique based on radiolabelled /? 2-M as the specific precursor molecule of /?2-M amyloidosis appears to be a more sensitive diagnostic method. Both tracer techniques have been used so far only in small single-centre clinical studies, and a more widespread application will require the introduction of recombinant material as the protein source for labelling. The 'gold standard' for the definit- ive diagnosis of /? 2-M amyloidosis, and also for refer- ence in the evaluation of new diagnostic techniques, remains the histomorphological demonstration of /?2-M amyloid by Congo red staining, green birefringence under polarized light, positive immunostaining with anti-/?2-M antibodies, and electronoptic visualization of amyloid fibrils in tissue obtained invasively by biopsy, surgery or autopsy.