Occurrence of psoriasis among Bulgarian patients with autoimmune bullous diseases over a 20-year period

Background: The coexistence of autoimmune bullous diseases (AIBD) and psoriasis (PsO) has been described in numerous case reports with a marked prevalence of bullous pemphigoid (BP). The aim of our study was to identify and characterize all patients with AIBD and coexisting PsO in the Department of Dermatology, Medical University-Sofia, Bulgaria over a 20-year period. A retrospective analysis was performed of all AIBD patients registered at the Immunopathology unit of our AIBD referral center during the period January, 2002 – June, 2022. The files of 1575 newly diagnosed AIBD patients were processed and searched for coexisting psoriasis. Coexistence of AIBD and PsO was found in 23 patients: 15 with BP, 7 with pemphigus, and 1 with dermatitis herpetiformis (DH). PsO preceded the occurrence of the AIBD with 36 to 600 months in all but one patient with DH. The mean age of onset of BP was 61 years, and of pemphigus - 65 years. Phototherapy, topical pesticides or biologic anti-psoriatic treatment could be suspected as triggering factors. All patients underwent different therapeutic regimens ranging from topical corticosteroids to biologic agents depending on the severity of the associated diseases. Our study confirmed the prevalence of BP among AIBD occurring in patients with PsO in Bulgaria, which is in contrast to the higher proportion of pemphigus in the dataset of AIBD cases diagnosed over the study period. Further research is required to delineate the underlying factors for this coexistence.