Rilzabrutinib-induced transition from pemphigus vulgaris to pemphigus foliaceous: a case report and literature review.

The discovery of the role of Bruton's Tyrosine Kinase (BTK) in inflammation and autoimmunity has recently led to the development of BTK inhibitors for the treatment of autoimmune diseases, including pemphigus vulgaris. We herein present the case of a patient affected by pemphigus vulgaris, refractory to conventional immunosuppressive therapies and to multiple courses of rituximab, who was treated with rilzabrutinib and achieved disease control, but whose immunological profile switched from pemphigus vulgaris to pemphigus foliaceus after drug discontinuation. Furthermore, we reviewed the literature to better characterize the phenotypic transitions from pemphigus vulgaris to pemphigus foliaceus reported so far. The factors underlying this transition are largely unknown, although it has been postulated that immunosuppressive therapies may be more effective against anti-desmoglein 3 (DSG3) antibodies compared to anti-desmoglein 1 (DSG1). However, further studies are needed to clearly define the effect of rilzabrutinib (and immunosuppressive therapies in general) on anti-DSG1 and anti-DSG3 antibodies.