Psoriasis is associated with increased risk of bullous pemphigoid: A nationwide population-based cohort study in Taiwan.

Psoriasis may coexist with bullous pemphigoid (BP); however, no cohort studies have investigated the relationship between psoriasis and the risk of BP. This study aims to investigate the relationship between psoriasis and the risk of BP in Taiwan. This cohort study consists of 109 777 psoriatic patients and 109 777 matched non-exposed controls. Psoriatic patients diagnosed between 2002 and 2012 were identified from the Taiwan National Health Insurance Research Database. The age-, sex- and index date-matched non-exposed group was selected from the same database. The relationship between psoriasis and the risk of BP was investigated using Cox proportional hazards analyses. Psoriasis was significantly associated with an increased risk of BP (hazard ratio, 3.05; 95% confidence interval, 2.10-4.43; P < 0.001). The mean interval between the diagnoses of psoriasis and BP was 2.86 years, with the highest occurrence in the first year after psoriasis diagnosis, and gradually decreasing with each year of observation. Psoriatic patients with BP were significantly younger than BP patients in the non-exposed group (71.6 ± 13.9 vs 76.6 ± 7.7 years, respectively; P = 0.030). A higher proportion of patients with coexisting psoriasis and BP received phototherapy (20%). In conclusion, psoriasis was independently associated with a 3.05-fold increased risk of BP, and psoriatic patients with BP were younger, with over one-third of BP cases diagnosed in the first year after incident psoriasis. Therefore, clinicians treating patients with psoriasis may be aware of the possibility of the development of BP.