Increased frequency of multiple sclerosis among patients with bullous pemphigoid: a population-based cohort study on comorbidities anchored around the diagnosis of bullous pemphigoid

Background Bullous pemphigoid (BP) is a disease of the elderly and may be associated with neurological and cardiovascular diseases and diabetes. Mortality rates strongly exceed those of the background population. Objectives To investigate the frequency of comorbidities and their temporal relation to BP. Methods A register-based matched-cohort study on all Danish patients with a hospital-based diagnosis of BP (n = 3281). The main outcomes were multiple sclerosis (MS), Parkinson disease (PD), Alzheimer disease (AD), stroke, diabetes types 1 and 2, malignancies, ischaemic heart disease (IHD), hypertension and eventually death. Results At baseline, patients with BP had increased prevalences of MS [odds ratio (OR) 9.7, 95% confidence interval (CI) 6.0-15.6], PD (OR 4.2, 95% CI 3.1-5.8), AD (OR 2.6, 95% CI 1.8-3.5) and stroke (OR 2.7, 95% CI 2.4-2.9). Furthermore, malignancies, cardiovascular disease and diabetes were over-represented among patients with BP: type 1 diabetes (OR 3.1, 95% CI 2.5-3.8), type 2 diabetes (OR 2.3, 95% CI 2.0-2.6), malignancies (OR 1.3, 95% CI 1.1-1.4), IHD (OR 1.7, 95% CI 1.5-1.9) and hypertension (OR 2.0, 95% CI 1.8-2.2). During follow-up, the risk of MS was significantly higher among patients with BP [hazard ratio (HR) 9.4, 95% CI 4.9-18.0], even if events during the first year after diagnosis of BP were excluded (HR 5.1, 95% CI 2.3-11.3). Patients with BP had an average increased mortality rate of 2.04 (95% CI 1.96-2.13). Conclusions We discovered a significantly increased frequency of MS among patients with BP. At the time of diagnosis, patients with BP had an excessive number of comorbidities and an increased mortality rate over the following years.