Selective IgM deficiency: evaluation of 75 patients according to different diagnostic criteria.

Selective IgM deficiency (SIgMD) has recently been included in the inborn errors of immunity classification. SIgMD has conflicting diagnostic criteria and diverse clinical and immunological findings. We aimed to assess the clinical and laboratory profiles of patients with SIgMD and to compare the data of patients diagnosed using two inclusion criteria. This was a descriptive, retrospective, observational, collaborative study. Patients were included according to the following definitions: Group 1, IgM levels < 0.20 g/L in children and < 0.30 g/L in adults, and Group 2, serum IgM levels below 2SD and, for both, absence of associated immunological diseases or secondary causes. The protocol was approved by the Ethics Committee, and patients provided consent. In total, 75 patients were included: 37 (16 M:21F; mean age, 52.92) and 38 (13 M:25F; mean age, 53.47) in Groups 1 and 2, respectively. The most frequent clinical manifestations were allergic rhinitis (G1, 45.9%; G2, 36.8%), asthma (G1, 37.8%; G2, 28.9%), and pulmonary infections (G1, 27.03%; G2, 21.05%). Chromosomopathies (16.22%) and neoplasia (13.51%) were more frequent in G1, whereas URTI (23.68%) and skin infections (23.68%) were more common in G2. There was no difference in sex or mean age at symptom onset between both groups of patients. Regarding the clinical picture, 90.7% of the lesions were benign (68/75). Chromosomopathies may be associated with SIgMD, suggesting the need to quantify serum IgM levels in these cases. Considering the possibility of developing autoimmunity, neoplasia, and common variable immunodeficiency, it is advisable to follow up patients with SIgMD.