Morphological and immunohistochemical (CD4/CD8 T cell and CD123(+) plasmacytoid dendritic cell ratios) comparative analysis of rosacea, discoid lupus erythematosus, and polymorphous light eruption lesions

BACKGROUND: Rosacea, discoid lupus erythematosus (DLE), and polymorphous light eruption (PLE) can present with overlapping clinical and histopathological features. This study aimed to compare the immunohistochemical and histopathological findings of these lesions and to evaluate the contribution of immunohistochemistry to the differential diagnosis. MATERIALS AND METHODS: Histopathological reevaluation was performed on previously diagnosed cases, including 27 DLE, 27 PLE, and 29 rosacea lesions. Immunohistochemical staining for CD4, CD8, and CD123 was conducted. The CD4/CD8 ratios of lymphocytic infiltrates and the rates of CD123-positive plasmacytoid dendritic cells (PDCs) were assessed. RESULTS: Significant differences were observed among the groups in several histopathological parameters, including follicular plugging ( P = 0.003), presence of Demodex ( P < 0.001), dermal edema ( P = 0.001), spongiosis ( P = 0.027), mucin deposition ( P < 0.001), and basement membrane thickening ( P < 0.001). The percentage of CD123-positive PDCs was significantly higher in DLE compared to rosacea ( P = 0.005). DLE also showed more clusters of ≥ 20 CD123-positive cells compared to PLE and rosacea ( P = 0.005). No statistically significant difference was found between the groups in terms of CD4/CD8 ratios ( P = 0.058). CONCLUSION: The findings highlight practical histopathological and immunohistochemical differences that assist in distinguishing these conditions. Edema and spongiosis favor a diagnosis of PLE, while follicular plugging, mucin deposition, basement membrane thickening, and high CD123-positive PDC ratios are more indicative of DLE. The presence of Demodex organisms supports a diagnosis of rosacea. These observations can contribute to more accurate diagnosis and targeted management.