Pemphigoid gestationis (PG) is a very rare pregnancy-associated autoimmune skin disease that is characterized by an itchy rash that progresses to form blisters. Initially, the rash appears around the navel before spreading to other parts of the body including the back, trunk, arms, and buttocks. Areas such as the face, scalp, palms, soles and mucous membranes are very rarely affected.
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Whilst PG may occur at any time during pregnancy or even throughout, it is most common during the second and third trimesters. There is a possibility that the rise in estrogen in these stages both triggers and aggravates the condition. Symptoms may lessen or spontaneously resolve towards the end of the pregnancy, but this is often short-lived. 75-80% of women will experience a flare around delivery.
The condition generally lasts 6 months with the majority of cases remitting within the first several weeks following delivery. However, in some unfortunate cases where the patients are older, it may remain active for years. PG is also likely to recur in subsequent pregnancies and may be more severe and at an earlier onset than previously.
Most fetuses are born unaffected, but neonatal PG does occur in 3% of pregnancies. Fortunately, the resulting blisters usually resolve with clearance of maternal antibodies over the course of roughly 3-4 months. The fetal risks associated with this include a raised chance of infant mortality due to low fetal birth weight at the time of premature delivery.
Unfortunately, the pathogenesis of PG remains unclear. It appears that following an immunological event, auto-antibodies of mainly the IgG1 subclass are produced that target and bind an extracellular domain of the carboxyl terminus of the bullous pemphigoid antigen (BPAg2 – also called BP180). BPAg2 is found within the basement membrane (the zone between the epidermis and the dermis).
Upon binding, the antigen-antibody complex activates a series of pathways thought to damage the dermal-epidermal junction and result in inflammation and separation of the epidermis from the dermis. This allows fluid to build up and create a blister.
Before the appearance of blisters, the rash in PG can look like that of numerous other skin diseases. Thus, there are diagnostic tests that have been outlined based on clinical picturing, direct immunofluorescence microscopy and serology.
A skin biopsy can useful in showing typical features of the subepidermal blistering. This is not a confirmation of PG, because such blistering may be microscopically similar to that seen in dermatoses such as bullous pemphigoid (BP) or epidermolysis bullosa acquisita (EBA).
Confirmation of PG is through direct immunofluorescence staining of the biopsy to reveal autoantibodies. In some cases, serum autoantibodies can also be detected with indirect immunofluorescence microscopy via a blood sample. Furthermore, the quantitative analysis of serum BP180 antibody level may be recommended, as it correlates with the degree of disease severity and could therefore allow accurate monitoring of treatment response.
Treatment of PG is primarily through forms of corticosteroid therapy. Generally, topical corticosteroids are used in mild cases whilst more severe cases require systemic corticosteroids. Fortunately, systemic corticosteroids used during pregnancy are generally safe.
Alternatively, the use of immunosuppressive medications including azathioprine or ciclosporin could also be effective in the treatment of PG. Importantly, the safety of their use in pregnancy or during breastfeeding would require careful and informed consideration.