Mucous membrane pemphigoid (MMP) rarely coexists with another autoimmune bullous disease (AIBD). Herein, we report an extremely rare MMP case who sequentially developed pemphigus foliaceus (PF). A 72-year-old man had been treated by azathioprine monotherapy for anti-BP180 MMP for 1.5 years. Clinical findings suggestive of PF, represented by scaly erythema and erosions, started to appear approximately 1 month after the episode of diarrhea. Serological and immunohistochemical examinations confirmed the diagnosis of PF. The mucocutaneous lesions were controlled by oral azathioprine and topical corticosteroids. To our knowledge, this is a previously unreported case of PF coexistent with MMP. A literature review of MMP cases associated with AIBD elucidated that 16 out of 18 cases simultaneously developed MMP and AIBD, while only two cases were diagnosed sequentially by the changes in clinical symptoms similar to our case. The titer of anti-desmoglein 1 antibodies lineally correlated with the changes in the severity of scaly erythema. Mild but noticeable exacerbation of mucosal erosion prior to the gradual increase in anti-BP180-NC16a antibodies was also noted. Unlike in other cases where MMP/AIBD coexisted, sequential development of autoantibodies in our case cannot be explained by the epitope-spreading theory as autoantigens are micro-anatomically isolated from one other. The preceding viral infection and/or continuous moderate inflammation due to azathioprine monotherapy for MMP might have contributed to the development of PF in our case.
© 2021 Japanese Dermatological Association.