Visual clues for the histopathological diagnosis of psoriasis

Objective: The histopathologic diagnosis of psoriasis remains challenging. This study aimed to uncover visual clues for the histopathologic diagnosis of psoriasis in patients whose lesions required differentiation from other inflammatory skin disorders. Methods: A retrospective analysis was conducted of 100 psoriasis biopsy sections. Sections of other inflammatory skin diseases were included as the control group. The psoriasis and control groups were compared regarding the pathological characteristics, including the ñ sign, hypogranulosis, and neutrophilic infiltration or pustules within the epidermis. We also summarized the clinical information and the classic and non-classic histological features of psoriasis. Results: Biopsy sections from 190 patients were analyzed. Of these patients, 100 had a confirmed clinicopathological diagnosis of psoriasis, while 90 were diagnosed with an inflammatory skin disorder other than psoriasis (control group). The ñ sign was present in 79.0% and 21.11%, respectively, of the lesional biopsy samples from the psoriasis and control groups. The combination of the ñ sign and neutrophil infiltration in the upper epidermis was present in 74.0% and 10.0%, respectively, of the lesional biopsy samples from the psoriasis and control groups. The combination of these two features had a sensitivity of 0.89 and specificity of 0.76 in distinguishing between the psoriasis and control groups. Conclusion: The ñ sign is a useful visual clue for the histopathological diagnosis of psoriasis. However, for some inflammatory skin disorders that are very similar to psoriasis, such as pityriasis rubra pilaris, the combination of the ñ sign and neutrophil infiltration in the upper epidermis is needed to distinguish the condition from psoriasis.