Diagnostic value of direct immunofluorescence in oral mucous membrane pemphigoid: a retrospective study

BACKGROUND: Mucous membrane pemphigoid (MMP) is an autoimmune blistering disease with heterogeneous clinical manifestations that is hard to diagnose. Direct immunofluorescence (DIF) is critical, but its role in multimodal frameworks is unclear. OBJECTIVE: To assess DIF's diagnostic performance in MMP and explore factors affecting its positivity patterns in multimodal workflows. METHODS: We retrospectively analyzed 79 suspected MMP patients, categorizing them into confirmed and non-confirmed groups based on clinical, histopathological, and serological criteria. DIF of perilesional mucosal biopsies showed linear deposits of IgG, IgA, IgM, C3, and fibrinogen along the basement membrane zone (BMZ). Diagnostic efficacy was assessed via ROC curve analysis. RESULTS: 55 cases were confirmed. Histopathology demonstrated subepithelial blisters in 51, with 100% specificity, 92.73% sensitivity (AUC = 0.964, p < 0.05). DIF identified 47 cases, with C3 (63.64%) and IgG (60.00%) most common, showing 85.45% sensitivity, 100% specificity, and 97.87% concordance with histopathology. Disease duration independently predicted positive IgM (p = 0.023). STUDY LIMITATIONS: This study is a single-center retrospective study with a limited sample size, which has certain limitations. CONCLUSION: DIF, 100% specific, aids histopathology in MMP diagnosis, especially with C3/IgG linear BMZ deposition. Notably, IgM positivity correlates with prolonged disease duration, suggesting DIF efficiency may link to disease stage.