Differential diagnosis
It is important to differentiate the prebullous stage of pemphigoid gestationis from other pregnancy-related dermatoses. These include polymorphic eruption of pregnancy (PEP), pruritic urticarial papules and plaques of pregnancy (PUPPP), erythema multiforme, prurigo annularis, intrahepatic cholestasis of pregnancy, and impetigo herpetiformis. Impetigo herpetiformis is not related to bacterial or viral causes, but is rather a manifestation of pustular psoriasis during pregnancy. The target lesions that form in pemphigoid gestationis look just like the target lesions of erythema multiforme.
When there is no blister formation, it is impossible to distinguish pemphigoid gestationis from many of the other cutaneous eruptions of pregnancy. If uncertain, the clinician should perform punch biopsies of the involved skin, with one specimen sent for immunofluoresence studies. The biopsy should not pass directly through a bullae, due to risk of losing the overlying epidermis in the specimen. Do the punch biopsy at the edge of the bulla including some normal skin. Other important laboratory exams to perform would include liver function tests to look for an upward trend associated with intrahepatic cholestasis, and herpes simplex virus antibody testing for the association with erythema multiforme. The cutaneous findings and pertinent tests are listed in the table below in order of increasing potential as a life-threatening dermatosis (TABLE).
TABLE
Differential diagnosis for blisters in pregnancy
| DISEASE | ASSOCIATIONS | DIAGNOSIS | TREATMENT |
|---|---|---|---|
| Polymorphous eruption of pregnancy | Nonspecific pruritic eruption of pregnancy | Biopsy to differentiate from prebullous stage of pemphigoid (herpes) gestationis | Mild to mid-potency topical steroids, oral antihistamines |
| Pruritic urticarial papules and plaques of pregnancy | Occur in stretch marks, spare umbilicus; more often in primigravidas | Unless history is very clear, biopsy to differentiate from prebullous stage of pemphigoid gestationis | Emollients, pulse-dye laser during violaceous stage of striae, topical steroids, oral antihistamines |
| Erythema multiforme | Can involve mucous membranes, targetoid lesions, absence of pruritus, centripetal spread, favors palms/soles | Viral, bacterial, or drug-related eruption. Most often with herpes simplex I or II virus. Biopsy to differentiate from pemphigoid gestationis | Acyclovir, valacyclovir if HSV-related, treatment of bacterial infection, or removal of offending drug |
| Pemphigoid gestationis | Blistering, urticarial papules/plaques, pruritus | Biopsy sent for histologic diagnosis and immunofluorescence | Prednisone for short course starting at 1 mg/kg, then tapering over 2–3 months, topical steroids |
| Intrahepatic cholestasis of pregnancy | +/- jaundice, otherwise no cutaneous findings other than generalized pruritus, risk of preterm birth | Elevation in liver function tests, cholesterol, triglycerides, dark urine, right upper quadrant pain, nausea, greasy stools | Ursodeoxycholic acid, S-adenosyl-L-methionine |
| Impetigo herpetiformis (pustular psoriasis of pregnancy) | Extremely ill with fever, chills, nausea, vascular instability, pustules rather than vesicles | Biopsy if uncertain, pustules sterile, risk of hypocalcemia, hypoparathyroidism | High dose oral steroids or cyclosporine |