Coexistence of SAPHO syndrome and IgG4-related disease with Upadacitinib.

Objectives: To describe the first reported case of coexisting Synovitis, Acne, Pustulosis, Hyperostosis, and Osteitis (SAPHO) syndrome and IgG4-related disease (IgG4-RD) and to evaluate the therapeutic response to Upadacitinib. Methods: We described the clinical course, investigations, treatments, and outcomes of a 45-year-old woman initially diagnosed with SAPHO syndrome who subsequently developed IgG4-RD. Laboratory tests, imaging findings, and therapeutic responses were analyzed. Results: The patient developed IgG4-RD-related organ involvement during the course of SAPHO syndrome. Although glucocorticoid therapy was initially effective, disease flares occurred upon tapering. Upadacitinib was initiated as an escalation therapy, leading to rapid improvement in clinical symptoms and normalization of inflammatory and IgG4-related serological markers. Sustained remission was maintained with continued treatment. Conclusion: This case demonstrates that Upadacitinib may be an effective therapeutic option for patients with concurrent SAPHO syndrome and IgG4-RD. The observed clinical response supports the potential role of JAK-STAT pathway modulation in managing overlapping immune-mediated disorders.