Simultaneous improvement of immunoglobulin G4-related disease complicated by nontuberculous mycobacteria infection by anti-infective therapy alone: a case-based literature review.

Immunoglobulin G4-related disease (IgG4-RD) is a systemic immune-mediated disease, and antigenic stimulation by allergen or malignancy is considered a potential pathogenesis. To date, IgG4-RD complicated by acid-fast bacterial infections, such as tuberculosis or nontuberculous mycobacteria (NTM), has been sporadically reported, and can be considered as potential antigens contributing to IgG4-RD onset. These cases pose a clinical dilemma because immunosuppressive therapy may exacerbate the underlying infection. Herein, we present a case of IgG4-RD complicated by NTM infection that was successfully treated solely with antimicrobial therapy. A 64-year-old male, initially treated for IgG4-related autoimmune pancreatitis with glucocorticoids, developed pulmonary lesions with elevation of IgG4 levels shortly after glucocorticoid cessation. While lung biopsy revealed typical IgG4-RD histology, culture specimens also identified concomitant infection of Mycobacterium intracellulare. Notably, following antimicrobial therapy for NTM, both the pulmonary lesions and serum IgG4 levels improved without re-administering glucocorticoids. Our literature review identified eight additional cases of IgG4-RD complicated by acid-fast bacterial infection, and two out of eight previous cases; three in total including the current case showed improvement of IgG4-RD using antibiotics alone. These findings raise the possibility that acid-fast bacteria could potentially serve as infectious antigens triggering IgG4-RD, and targeting the underlying infection can be a therapeutic strategy, not only for infection, but also for IgG4-RD, while further studies are warranted.