Histopathological features of pemphigoid gestationis and polymorphic eruption of pregnancy: A blinded retrospective comparative study of 31 cases

Pemphigoid gestationis (PG) and polymorphic eruption of pregnancy (PEP) are pregnancy-related dermatoses. Definitive diagnosis often relies upon histopathology and direct immunofluorescence (DIF). PG is associated with fetal and neonatal risks, while PEP confers minimal risk.We aimed to compare histopathologic features to determine key differentiators.A retrospective cohort study of PG and PEP cases, with accompanying DIF, conducted from 1995 to 2020. Skin biopsies were examined independently in a blinded fashion by two dermatopathologists for a list of histopathological features.Twenty-one cases of PG and 10 cases of PEP were identified. PG had significantly denser eosinophils than PEP (mean 155 vs. 48 cells/5 hpf; p 0.018). PG was also noted to have eosinophilic spongiosis and eosinophils at the dermal-epidermal junction more frequently compared to PEP (80% PG vs. 10% PEP; p 0.001). A mean cutoff value of 86 eosinophils and a mean optimal sensitivity and specificity of 81% and 83%, respectively, for eosinophils density's diagnostic power of PEP versus PG were achieved. Subepithelial separation was exclusively seen in PG (40% vs. 0%; p 0.007).Eosinophilic spongiosis, eosinophilic epitheliotropism, and dense superficial dermal eosinophils were diagnostic of PG. Given overlapping clinicopathologic features, however, DIF results with clinicopathologic correlation, remain the gold standard.