Detection of intracellular IgD using flow cytometry could be a novel and supplementary method to diagnose IgD multiple myeloma

We examined whether detecting the heavy chain of cytoplasmic immunoglobulin D (IgD) by flow cytometry could be used as a supplemental method to diagnose IgD multiple myeloma (MM). Bone marrow (BM) samples of thirty-five patients with MM were collected. Five of them were IgD MM, the rest of thirty were other subtypes of MM. Antibodies to four types of heavy chains of immunoglobulin (e.g., IgA, IgG, IgM, and IgD) were analyzed by flow cytometry in each patient's BM sample. The five IgD MM patients were all positive for cytoplasmic IgD. The percentage of IgD positive MM cells among nucleated cells varied from 0.4 to 12.9%. Cytoplasmic IgG was positive in eight patients with IgG MM (n = 9); cytoplasmic IgA was positive in all patients with IgA MM (n = 10); cytoplasmic IgM was positive in one patient with IgM MM (n = 1). No heavy chain was detected in light chain MM (n = 9) and non-secretory subtype (n = 1). Detection of cytoplasmic IgD by flow cytometry is a convenient, sensitive and supplemental method to diagnose IgD MM.