Increased risk of venous thromboembolism in patients with bullous pemphigoid. The INVENTEP (INcidence of VENous ThromboEmbolism in bullous Pemphigoid) study

Activation of blood coagulation has been demonstrated in bullous pemphigoid (BP), a rare autoimmune blistering disease, potentially leading to a prothrombotic state. In order to evaluate the incidence of venous thromboembolism (VTE) in BP, a cohort study was carried out on 432 BP patients (59 % females; median age 76 years, interquartile range [IQR]: 68-82). At diagnosis, autoimmune bullous skin disorder intensity score (ABSIS) was calculated. VTE incidence was standardised with rates of the general population. Multivariable Cox proportional hazard model was used to estimate the hazard ratio of VTE according to ABSIS and concomitant risk factors. During a median follow-up of 4.2 years, 31 objectively-diagnosed VTE events were recorded. The incidence rate of VTE (per 1000 patient-years) was 17.2 overall (95 % confidence interval [CI]: 11.1-23.2), 56.7 (95 %CI: 33.0-80.4) during acute phase (22 VTE) and 6.3 (95 %CI: 2.8-11.3) during remission (9 VTE). The standardised incidence ratio was 4.06 (95 %CI: 2.73-5.65), higher during the acute phase (14.86, 95 %CI: 9.20-21.88) than during remission (1.48, 0.66-2.63). The adjusted hazard ratio of VTE was 2.74 (95 %CI: 1.07-7.04) for ABSIS > 48 vs ABSIS < 28, and 2.56 (95 %CI: 1.00-6.70) in patients with ≥ 2 concomitant risk factors. In conclusion, BP patients have a 15-fold increased VTE risk during acute phase, proportional to disease severity and heightened by concomitant risk factors.