Unusual myelomas: a review of IgD and IgE variants

Immunoglobulin D multiple myeloma (IgD MM) accounts for almost 2% of all myeloma cases. It is associated with an increased frequency of undetectable or small monoclonal (M)-protein levels on electrophoresis; osteolytic lesions; extramedullary involvement; amyloidosis; a lambda (lambda) light chain predilection; renal failure; hypercalcemia; and, often, advanced disease at diagnosis. Immunoglobulin E (IgE) MM is rare, with fewer than 50 cases reported in the literature. IgE MM presents with features similar to those of IgD MM, along with a higher incidence of plasma cell leukemia. The hallmark of IgE MM is t(11;14) (q13;q32). IgD and IgE levels are generally very low and hence may escape detection; thus, it is important that, when myeloma is suspected, patients be screened for the presence of IgD and IgE if they have an apparently free monoclonal immunoglobulin light chain in the serum. Although survival of patients with IgD MM or IgE MM is shorter in comparison to those with immunoglobulin G (IgG) MM or immunoglobulin A (IgA) MM, the outcome for patients with IgD and IgE subtypes is improving with the use of novel agents and autologous transplantation.