Oral mucous membrane pemphigoid as a window to systemic autoimmunity: two cases associated with rheumatoid arthritis and Sjögren's disease.

Mucous membrane pemphigoid is a rare chronic autoimmune bullous disease that predominantly affects mucosal surfaces and may lead to significant morbidity when diagnosis is delayed. Increasing evidence suggests that oral manifestations may serve as reliable early indicators of systemic immune dysregulation and can precede the recognition of other autoimmune disorders. We report two cases of oral mucous membrane pemphigoid associated with systemic autoimmune diseases, emphasizing that the oral cavity is a sentinel site for systemic autoimmunity and highlighting the importance of integrated diagnostic and therapeutic strategies. In the first case, a 68-year-old woman with longstanding rheumatoid arthritis presented with recurrent oral ulcerations that were histopathologically confirmed as mucous membrane pemphigoid. During follow-up, ocular involvement was identified as peripheral ulcerative keratitis related to rheumatoid arthritis, requiring adjustment of systemic immunosuppressive therapy. Switching to B-cell depletion therapy with rituximab resulted in the control of both the extra-articular rheumatoid arthritis manifestation and mucous membrane pemphigoid activity. In the second case, a 44-year-old woman presented with desquamative gingivitis and oral bullous lesions. After a biopsy confirmed mucous membrane pemphigoid, progressive sicca symptoms prompted rheumatological investigation, leading to the diagnosis of Sjögren's disease based on serology, imaging, and minor salivary gland biopsy. Treatment with azathioprine resulted in the clinical stabilization of both diseases. These cases illustrate how oral lesions may reveal or precede systemic autoimmune disease and underscore the diagnostic challenges of overlapping immune-mediated rheumatic diseases. Recognizing shared immunopathogenic pathways may enable the selection of targeted therapies that simultaneously control multiple autoimmune conditions, thereby improving disease control and reducing the treatment burden.