Clinical and Immunological Characteristics of Bullous Pemphigoid Patients With Psoriasis Comorbidity: A Retrospective Study.

Despite the recognized association between bullous pemphigoid (BP) and psoriasis, the clinical and immunological profiles, and inflammation patterns of coexistence remain undefined. We therefore conducted a retrospective cohort study of 140 BP patients without psoriasis (BP alone group) and 24 BP patients with comorbid psoriasis (BP-PsO group) to characterise these features. Average age of BP onset was significantly lower in the BP-PsO group, compared with the BP alone group (median [IQR]: 67.00 [58.00-75.75] years vs. 75.00 [64.00-82.00] years) (p = 0.021). In the BP-PsO group, 21 patients (87.5%) had coexisting active psoriatic plaques and BP lesions. The overall disease activity of BP was comparable between the BP-PsO and BP alone groups, both showing typical BP immunological features. Serum IL-17A level was significantly elevated in the BP-PsO group (median [IQR]: 18.29 [10.39-43.50] pg/mL), compared with the BP alone group (median [IQR]: 10.36 [9.16-12.11] pg/mL) and psoriasis alone groups (median [IQR]: 11.65 [10.10-12.78] pg/mL), and correlated with disease activity. Flow cytometry confirmed enhanced IL-17A response in peripheral blood mononuclear cells from the BP-PsO group, with an elevated proportion of CD4+ IL-17A+ cells and IL-17A+ T follicular helper cells versus corresponding controls. IL-13 was comparably elevated in both the BP-PsO and BP alone groups, relative to psoriasis alone group and healthy controls. In a representative case, inhibition of IL-17A led to concurrent remission of both diseases. BP with psoriasis shares foundational features with idiopathic BP, but represents a distinct clinical entity characterised by a predominant IL-17A signature, highlighting its potential as a therapeutic target.