Mihaela Fülle, Dieter Metze, Almut Böer-Auer, Nani Osada, Stephan A. Braun
DOI: 10.2340/00015555-3817

The histopathology of psoriasis can lack classical features on certain anatomical sites. The aim of this study was to detail the histopathology and immunophenotype of psoriasis on the legs, in order to differentiate it from other inflammatory dermatoses, such as stasis dermatitis. The histopathology of psoriasis on the legs was retrospectively compared with psoriasis on the trunk and stasis dermatitis. Statistically, psoriasis on the legs was significantly less likely to show typical histological criteria of psoriasis, such as regular hyperplasia, suprapapillary thinning, and “kissing vessels”. The most valuable criteria to distinguish psoriasis on the legs from stasis dermatitis were the presence of neutrophils in the cornified layer and staggered parakeratosis. In addition, an immunohistochemical panel (Ki-67, Bcl-2alpha, S100A7, CD3, MPO, CK10, CK16) revealed that staining with Ki-67 and MPO could be diagnostically useful. Since the cornified layer contains important histopathological clues to differentiate psoriasis on the legs from stasis dermatitis, clinicians should refrain from unnecessary rubbing during disinfection before taking a biopsy.

Diagnosis of psoriasis is usually made clinically, but in some cases clinicians take biopsies to confirm the diagnosis or to exclude differential diagnoses. Psoriasis on the lower extremities can lack classical histological criteria of psoriasis, and therefore histological diagnosis can be challenging at this specific anatomical site. This study systematically analysed the histology, including the immunohistochemistry, of psoriasis on the legs, and identified characteristic criteria for this location. The results help to improve the histological diagnostic reliability of psoriasis on the legs, and provide practical information for clinicians on what to consider when taking biopsies.