A case of immunoglobulin G4-related disease complicated by atopic dermatitis responsive to upadacitinib treatment.

Immunoglobulin G4-related disease (IgG4-RD) is mainly treated with glucocorticoids. In many cases, this disease is resistant to glucocorticoids, and their toxicity can be a problem. We encountered a patient with IgG4-RD affecting multiple organs (such as the skin, lung, and lacrimal gland), who had comorbidities, including atopic dermatitis and diabetes. In this case, while glucocorticoid tapering was difficult, the introduction of upadacitinib resulted in the remission of both atopic dermatitis and IgG4-RD without glucocorticoid dose escalation. Peripheral blood flow cytometry analysis showed that the proportions of activated non-Th1/Th17 cell subset (Th2 cells), follicular helper T cells, and plasmocytes were increased before upadacitinib therapy, but all normalised after treatment. Interleukin-4 and interleukin-21 signals are important for the differentiation of CD4+ T cells into type 2 helper T or B cells in the peripheral blood. Our case suggested that inhibition of Janus kinase 1, which mediates these signals, might have contributed to improved pathological conditions in IgG4-RD.