Bullous pemphigoid

Bullous pemphigoid (BP) is the most common autoimmune subepidermal blistering disease and primarily affects older adults. In BP, the immune system produces autoantibodies against proteins in the basement membrane zone, especially BP180/type XVII collagen and BP230, which help anchor the outer layer of skin to the underlying tissue. This immune attack causes inflammation and separation between skin layers, leading to intense itching and large, tense, fluid-filled blisters. BP primarily affects the skin, but mild mucous membrane involvement may occur in a minority of people.

Itchy skin that may appear months before blisters form, red or darker urticarial plaques, eczema-like rashes, large tense blisters that do not break easily, blisters along skin folds or flexural areas such as the lower abdomen, thighs, armpits, and groin, crusted erosions after blisters break, and, less commonly, small mouth sores or other mild mucosal lesions.

Bullous pemphigoid is associated most strongly with neurological diseases, including dementia, Parkinson’s disease, stroke, epilepsy, and multiple sclerosis. It has also been associated with psoriasis, lichen planus, rheumatoid arthritis, lupus, thyroiditis, polymyositis, and thromboembolic disease.

Risk increases sharply with age, and BP most often affects people over 70. The disease is associated with genetic susceptibility, especially certain HLA variants, as well as neurological disease, aging-related immune changes, and other autoimmune or inflammatory conditions. Reported triggers include certain medications, especially DPP-4 inhibitors used for type 2 diabetes, immune checkpoint inhibitors, some diuretics, antibiotics, and antipsychotics, as well as ultraviolet radiation, trauma, burns, surgery, radiotherapy, infections, and, less commonly, vaccination or transplantation.