A New Variant of Heavy-Chain Disease (μ-Chain Disease)

Abstract

A pathologic immunoglobulin was found in the serum of a man who had the clinical signs of a malignant lymphoproliferative disorder. It represents a new variant of heavy-chain disease (μ-chain disease). Additional findings included radiographic evidence of skeletal involvement, amyloidosis and morphologic abnormalities of the plasma cells. Although serum electrophoresis did not reveal an M component, immunoelectrophoresis showed an anomalous protein that appeared to be a rapidly migrating IgM. This protein was subsequently identified as a heavy-chain fragment of IgM. The urinary findings were unique in that the μ-chain fragment demonstrated in the serum was absent and a light chain (kappa type) was present.