Rare myelomas: sometimes when you hear hooves, it's a zebra...

The review by Drs. Pandey and Kyle[1] highlights important facets of the management and diagnosis of rare subtypes of myeloma. Immunoglobulin D multiple myeloma (IgD MM) affects less than 2% of all patients with myeloma, and only about 50 cases of immunoglobulin E (IgE) MM have been described in the literature.[2,3] Based upon the rarity of these subtypes, few series of either subtype are reported, and most only when they present to tertiary referral centers; as a consequence, IgD MM and IgE MM are subject to referral bias, rendering their true natural history and frequency much more challenging to interpret. Drs. Pandey and Kyle raise some important issues. The use of newer methods of disease assessment that focus on minimal residual disease (MRD) may facilitate the long-term evaluation of these myeloma patients, even if the rare Ig subtype is not identified at diagnosis.