Diagnostic approach to and follow-up of difficult cases of AL amyloidosis

Background. Routine electrophoretic analysis fails to detect a monoclonal component (MC) in a considerable portion of AL amyloidosis patients. We investigated whether the combination of immunofixation (IF) on agarose gel electrophoresis and bone marrow plasma cell (BMPC) light chain κ/λ. ratio analysis could contribute to diagnosis in these cases. The possible use of the BMPC κ/λ ratio in monitoring the clone was also investigated. Methods, We performed BMPC κ/λ ratio analysis and IF of serum and urine in 16 selected patients with no detectable MC at routine analysis, despite clinical features suggestive of primary amyloidosis. An anti-idiotypic monoclonal antibody specific for the amyloidogenic immunoglobulin and the BMPC κ/λ ratio were used to monitor the clone in a patient who underwent autologous peripheral blood stem cell transplantation. Results. Abnormal κ/λ ratios were found in 14 (sensitivity 87.5%), and a MC in 12 (sensitivity 75%). Combination of the two analyses confirmed diagnosis in all cases. In one patient changes in the size of the done, monitored on serial bone marrow aspirates by an anti-idiotypic antibody, paralleled variations of the κ/λ ratio. Conclusions. This study demonstrates that the combined use of IF and the BMPC κ/λ ratio is extremely powerful in AL amyloidosis. In addition, the BMPC κ/λ ratio should be considered for monitoring the amyloidogenic clone when serum or urine MC is not quantifiable.