Patients with bullous pemphigoid and comorbid psoriasis present with less blisters and lower serum levels of anti-BP180 autoantibodies

Background: Although the association of bullous pemphigoid (BP) and psoriasis is well-established, the clinical and immunological features of patients with coexisting BP and psoriasis are yet to be investigated. Objective: We aimed to estimate the prevalence of psoriasis amongst patients with BP and to elucidate the clinical and immunological characteristics of BP patients with comorbid psoriasis. Methods: A retrospective cohort study including all consecutive patients diagnosed with BP throughout the years 2009–2019 in a tertiary referral centre. Results: The study encompassed 273 patients with BP, of whom 11 (4.0%; 95% CI, 2.3–7.1%) had comorbid psoriasis. The onset of psoriasis preceded that of BP in 81.8% of patients by a median (range) latency of 26.5 (5.0–34.0) years. Compared to BP patients without psoriasis, those with BP and comorbid psoriasis were significantly younger at the onset of BP [71.8 (9.3) vs. 79.4 (9.8) years; P = 0.023], had a milder erosive phenotype [erosion/blister BPDAI mean (SD)score; 5 (4.1) vs. 22.3 (15.2); P = 0.025], lower levels of anti-BP180 NC16A serum autoantibodies [236.6 (266.3) vs. 556.2 (1323.6) U/mL; P = 0.008] and a higher prevalence of isolated linear C3 deposits (36.4% vs. 14.1%; P = 0.043) and a lower prevalence of linear immunoglobulin G deposits (36.4% vs. 68.7%; P = 0.025) along the dermal–epidermal junction by direct immunofluorescence microscopy. Conclusions: Patients with BP and comorbid psoriasis present at a younger age with milder erosive phenotype and lower levels of pathogenic autoantibodies.