Visual Clues for the Histopathologic Diagnosis of Psoriasis: A Retrospective Case-Control Study

Abstract

Objective: The histopathologic diagnosis of psoriasis remains challenging. This study aimed to uncover clues for the histopathologic diagnosis of psoriasis in patients whose lesions required differentiation from other inflammatory skin disorders. Methods: A retrospective analysis was conducted between psoriasis biopsy sections and other inflammatory skin diseases sections. 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 histologic features of psoriasis. Comparisons between psoriasis and control groups were performed using the c-square test. 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 classic histologic features included the mound of parakeratosis (68.0%), confluent parakera tosis (42.0%), hypogranulosis (86.0%), regular psoriasiform hyperplasia (79.0%), Munro microabscess (85.0%), spongiform pustule of Kogoj (43.0%), suprapapillary plate thinning (87.0%), and dermal papilla capillary ectasia (98.0%). The ñ sign was present in 79.0% and 21.1%, respectively, of the lesional biopsy samples from the psoriasis and control groups (P < 0.001). 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 (P < 0.001). The combination of these 2 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 histopathologic 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.