Pemphigus Vulgaris - Pathophysiology

Pathophysiology

See also: List of human leukocyte antigen alleles associated with cutaneous conditions

It is an autoimmune disease caused by antibodies directed against both desmoglein 1 and desmoglein 3 resulting in the loss of cohesion between keratinocytes in the epidermis, classified as a type II hypersensitivity reaction. It is characterized by extensive flaccid blisters and mucocutaneous erosions. The severity of the disease, as well as the mucosal lesions, is believed to be directly proportional to the levels of desmoglein 3. Milder forms of pemphigus (like foliacious and erythematoses) are more desmoglein 1 heavy. It arises most often in middle-aged or older people, usually starting with a blister that ruptures easily. The lesions can become quite extensive. The pathogenesis of the disease involves autoantibodies against desmosome proteins, separating keratinocytes from the basal layer of the epidermis. On histology, the basal keratinocytes are usually still attached to the basement membrane leading to the appearance and thus the term, "tombstoning".

Transudative fluid accumulates in between the keratinocytes and basement membrane (suprabasal split), forming a blister and resulting in what is known as a positive Nikolsky's sign. This is a contrasting feature from bullous pemphigoid, where the detachment occurs between the epidermis and dermis (subepidermal bullae).