Histopathological diagnosis of psoriasis and psoriasiform dermatitides

Abstract

The term psoriasiform dermatitis encompasses a group of skin diseases with lesions that exhibit clinical and histological similarities to psoriasis. Conditions such as pityriasis rubra pilaris, seborrheic dermatitis, and psoriasiform keratosis share alterations in certain pathogenetic mechanisms. These common mechanisms result in similar epidermal changes that define the psoriasiform pattern, characterized by regular acanthosis and abnormal cornification, often accompanied by corneal and subcorneal neutrophilic infiltrates. Despite these epidermal similarities, the dermal alterations can vary significantly among psoriasiform dermatoses. For instance, psoriasis typically presents with mild, non-specific superficial inflammation, whereas pityriasis lichenoides chronica is marked by abundant lymphocytic infiltrates, endothelial damage, and erythrocyte extravasation. Furthermore, the psoriasiform pattern frequently appears alongside other histopathological patterns. Spongiosis is a common finding, which may be incidental in psoriasis or a defining feature in seborrheic dermatitis. Lichenoid infiltrates are a defining feature in conditions such as pityriasis lichenoides chronica and pityriasis rubra pilaris and are also seen in psoriasiform cases of syphilis. Understanding the histological commonalities and distinctions, along with the clinical features of each condition, enables dermatopathologists to differentiate between various psoriasiform dermatoses and to identify specific disease entities based on their typical histopathological and clinical presentations.