Diagnostic Usefulness of Immunohistochemical Staining for EMA in Psoriasis and Atopic Dermatitis Showing Psoriasiform Hyperplasia.

BACKGROUND

Atopic dermatitis (AD) and psoriasis (PSO) can share clinical and histopathologic features, complicating differentiation. Epithelial membrane antigen (EMA), a marker of epithelial differentiation, is used primarily in neoplastic diseases but is rarely assessed in inflammatory dermatoses. EMA expression in AD remains poorly defined.

OBJECTIVE

To evaluate whether EMA immunohistochemistry (IHC) helps distinguish PSO from AD with psoriasiform hyperplasia.

METHODS

We retrospectively reviewed 15 AD and 15 PSO patients showing psoriasiform hyperplasia. Clinical, histopathologic features, and EMA IHC patterns were assessed to compare AD and PSO.

RESULTS

Clinically, lichenification was more frequent in AD (80.0%) than in PSO (20.0%). Histopathologically, dilated capillaries were more frequent in PSO (100.0%) than in AD (46.7%), whereas dermal eosinophils were present in AD (73.3%) but not in PSO (0%); both differences were statistically significant. Moderate-to-severe acanthosis, parakeratosis, suprapapillary plate thinning, pallor of the upper epidermis, Munro's microabscesses, and diminished granular layer tended to be more frequently observed in PSO, without statistical significance. Regarding EMA, strong expression was more common in AD (73.3%) than in PSO (6.7%), with overlap in moderate staining intensity. The mean intensity grade was significantly higher in AD than in PSO (3.93 vs. 1.93). Diffuse epidermal expression was also more frequent in AD (86.7% vs. 16.7%) among EMA-positive cases.

CONCLUSION

EMA IHC may provide adjunctive evidence when distinguishing PSO from AD with psoriasiform hyperplasia. Strong and diffuse epidermal EMA expression may favor AD. Because intensity patterns can overlap, EMA should be interpreted in conjunction with clinical and histopathologic features.