Comorbid diseases in bullous pemphigoid: A population‐based case–control study

Bullous pemphigoid (BP) is the most prevalent autoimmune blistering disorder, triggered by autoantibodies targeting hemidesmosome components. It is associated with substantial morbidity and increased mortality. No studies comprehensively evaluate all comorbidities before and after diagnosing patients with BP. We aimed to investigate all BP-associated comorbid diseases and their patterns of associations. This nationwide population-based study included 5066 patients with BP and 10 132 controls between 2011 and 2021. We performed an automated mass screening of 546 diagnostic codes to identify BP-associated comorbidities 5 years before and after BP diagnosis, and analyzed associations patterns of comorbidities. Patients with BP had increased odds of having pressure ulcers, intracerebral hemorrhage, scabies, neuropsychiatric disorders, psoriasis, drug eruption, and acute renal failure before BP diagnosis. After BP diagnosis, they had increased odds pneumonia, sepsis, chronic renal disease, and cardiac arrest. Strong interrelationships were observed between five neuropsychiatric conditions before BP diagnosis and a strong bidirectional association between Alzheimer's dementia and pneumonia after BP diagnosis. This large case-control study of patients with BP thoroughly identified all relevant comorbidities before and after BP diagnosis, highlighting their clinical significance as predisposing and prognostic factors in patients with BP.