A case of benign immunoglobulin D monoclonal gammopathy of undetermined significance with 26 years of follow-up

The presence of a serum immunoglobulin D (IgD) monoclonal protein (M-protein) is seen in < 1% of patients with monoclonal gammopathies and is usually indicative of a malignant plasma cell disorder. Only a few cases of well-documented benign monoclonal gammopathy of undetermined significance (MGUS) of IgD subtype have been reported, and only 2 of those had over 5 years of follow-up at the time they were reported. Herein we describe longer-term follow-up of one of those 2 patients who has subsequently passed away from unrelated causes but never developed multiple myeloma or amyloidosis after 26 years of follow-up. Although IgD MGUS is extremely rare, this case confirms that presence of an IgD M-Protein is not always synonymous with a malignant plasma cell process.