Bullous pemphigoid (BP) is a condition that affects the skin with an autoimmune etiology. It is often seen in those over the age of 80 and the prevalence is even higher in elderly people with neurological comorbidities such as stroke, Parkinson disease and dementia.
It is generally prevalent in people after the fifth decade of life and may occur in younger adults. However, it is rare in infants and children. There is no predisposition towards either sex or associations with HLA to indicate a genetic risk factor.
Clinical signs and symptoms
The first symptom is often intense itchiness. The skin may develop large areas that are raised before the onset of tense fluid-filled blisters called bullae. These blisters are usually surrounded by areas of either visually normal or inflamed, red skin. Eventually, the blisters burst and leave behind a mark that will crust over. Oral blisters are rare. Instead, blisters tend to arise more in the flexures of joints like inside the elbows or behind the knees.
The pathogenesis of Bullous pemphigoid is characterized by the action of autoantibodies directed at target antigens responsible for either cell-to-cell adhesion within the epidermis (skin's outermost layer) or adhesion of squamous epithelium to the dermis (the layer next to the epidermis).
The mechanism that leads to the autoimmune process is still not known. We do know that when it occurs in bullous pemphigoid, primarily IgG autoantibodies are directed towards the basement membrane zone. More specifically, they target the residential bullous pemphigoid antigens BP180, or less frequently BP230. These are components of the hemidesmosome adhesion complex at the basement membrane, which ensures the epidermal cell layer is secured to the dermis to form a waterproof seal.
The autoimmune action in bullous pemphigoid affects the basement membrane zone between the epidermis and dermis. The autoantibodies that bind to the target antigens may lead to a series of immunological reactions, which eventually lead to the destruction of the hemidesmosomes. Ultimately, the skin layers begin to separate and fluid accumulates between them to cause the formation of subepidermal blisters.
Diagnosis and treatment
The diagnosis of BP is often through clinical examination followed by confirmation through a biopsy of the affected tissue. Pathological evaluation of the biopsy can reveal inflammation of the affected skin. Further testing of the biopsy specimen can be used to reveal the location of the autoantibodies in the basement membrane layer or mucosal membrane.
Treatment aims to make the disease tolerable by decreasing the rate at which bullae form. As the majority of those affected are elderly, treatment can become more complicated, because these patients often present with other comorbidities. This makes them more susceptible to the side-effects from systemic agents.
Therapy can vary depending on the severity of the presenting case. Mild or non-extensive cases may benefit from twice daily application of potent topical steroids. In support of this, there has been research suggesting that large quantities of high-potency topical corticosteroids applied to the affected surface are safer than oral corticosteroids in controlling localized bullous pemphigoid. On the other hand, moderate to severe cases require systemic steroids. Oral prednisolone is the predominant established treatment used for rapid, definite remission.