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

ABSTRACT 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.