Low IgM and infections in adults with autoimmune rheumatic diseases

Researchers retrospectively reviewed 257 adult inpatients in China who had autoimmune rheumatic diseases (ARDs) and persistent isolated low serum IgM. The cohort’s median age was 48 years, and 79.0% were women. Systemic lupus erythematosus was the most common ARD (53.7%), followed by primary Sjögren’s syndrome (19.8%) and rheumatoid arthritis (6.2%). The study assessed clinical features, infections, treatment history and laboratory parameters.

Pneumonia was recorded in 125 patients (48.6%). Low IgM was first identified before immunosuppressive treatment in 39 patients (15.2%); the other 218 (84.8%) had received immunosuppressive treatment before it was documented. Intravenous immunoglobulin use was documented in 40 patients (15.6%). Older age was independently associated with documented infection (OR 1.049; P=0.002).

The findings show that persistent isolated low IgM was present before immunosuppressive therapy in a subset of this cohort, but do not establish its cause or whether it increases infection risk. This retrospective inpatient study is limited to adults with ARDs in China; further research is needed to clarify the phenotype’s mechanisms and clinical significance.