Histopathologic Characterization of Untreated and Treated Psoriasis: A Cross‐Sectional Study

BACKGROUND: The histopathological presentation of psoriasis may vary depending on the timing of the biopsy, prior treatments utilized, and the presence of secondary skin changes. Consequently, dermatopathologists play a pivotal role in ensuring an accurate diagnosis, particularly when the psoriatic histopathology deviates from the classic features. This study aims to compare the prevalence of classic and non-classic histopathologic features of psoriasis between untreated and treated psoriasis. METHODS: This is a review of 109 biopsies of psoriasis from 2015 to 2021 obtained from a single institution. The cases were reviewed by two independent dermatopathologists who were blinded to the assigned groups (untreated, n = 62, and treated, n = 47). A 20-item histopathologic grading criterion, comprising both classic and non-classic features of psoriasis, was used for assessment. RESULTS: The prevalence of both classic (p = 0.274; CI: -0.169, 0.593) and non-classic (p = 0.456; CI: -0.526, 0.236) histopathologic features of psoriasis did not differ between untreated (classic = 78%, non-classic = 27%) and treated (classic = 76%, non-classic = 29%) groups. A comparison of each histopathologic feature did not vary between groups (p > 0.05). CONCLUSIONS: Psoriasis is a dynamic condition under the microscope. Classic histopathologic features of psoriasis seem to persist despite treatment. Non-classic features may also occur regardless of the treatment status. Hence, the presence of these features should not preclude the tissue diagnosis of psoriasis.