Herpes gestationis (HG) is a rare bullous dermatosis of pregnancy and the postpartum period. Disease onset is typically during the 4th to 7th months of pregnancy. However, it may occur during the 1st trimester or in the postpartum period. HG may or may not recur with subsequent pregnancies, but if it does, it typically begins earlier on in the pregnancy. Patients may also experience flares with the first few postpartum menses, with oral contraceptives, or with hormone-producing tumors.
Clinically, lesions may present as red edematous papules, urticarial plaques, vesicles, large tense bullae, erosions, or crusts. Milder cases may present with only a few red papules or with isolated urticarial plaques. Lesions are typically located on the abdomen but they may spread to other areas. This condition is usually extremely pruritic. Mucosal surfaces tend to be spared.
HG is an acquired autoimmune disorder that occurs secondary to the formation of IgG antibodies that interact with bullous pemphigoid antigen 2 (180 kDa hemidesmosomal transmembrane antigen, also known as type XVII collagen). Once deposited, these antibodies activate the complement cascade which in turn generates an inflammatory response and the cutaneous features of inflammation. Blister formation is in the lamina lucida on electron microscopic exam. Histopathologic evaluation reveals liquefaction degeneration and spongiosis in the epidermis with eosinophilic infiltration and edema in the dermis. Vesicular and bullous lesions show subepidermal separation, typically in a teardrop shape. Direct immunofluorescence of perilesional or urticarial skin demonstrates linear deposition of C3 along the basement membrane zone with concomitant IgG deposition in approximately 30 to 40% of patients. Indirect IF is positive in only about 20% of patients.
Children born to affected mothers may have similar lesions that resolve during the first weeks of life, but most have no skin lesions. Whether or not this condition is associated with fetal death, premature delivery, and small-for-gestational age infants is controversial.