Selective immunoglobulin M deficiency: An underestimated immunodeficiency disorder – not so rare

Immunoglobulin M (IgM) is the first antibody to be produced during an immune response, and most of the primary humoral immune response is mediated by IgM. Selective IgM deficiency (sIgMD) is a rare immune disorder that has been reported in the association with serious infections. Patients with sIgMD may be asymptomatic; however, approximately 80% of patients present with infections with bacteria, viruses, or protozoa or with an associated allergic, malignant, or autoimmune condition. sIgMD is usually identified when evaluating a patient for recurrent or serious infections. Attempts should be made to document the infection, as well as the responsible organism, whenever possible. It is a diagnosis of exclusion, and formal diagnostic criteria have not been established. We report three adult cases that were diagnosed to have sIgMD during the evaluation for serious polymicrobial infections with bacteria, fungi, mycobacterium, and viruses. One of them was diagnosed to have associated lymphocytic leukemia. All were successfully managed with intravenous Immunoglobulin (Ig), antibiotics, antiviral, supportive treatment, and discharged. We conclude that patients presenting with polymicrobial infections with encapsulated bacteria, fungi, mycobacterium, and viruses should be evaluated for specific antibody deficiency responses, and they appear to improve clinically on Ig therapy. It appears that the disorder is underdiagnosed.