Direct Immunofluorescence Intensity as a Supportive Marker of Clinical Severity in Pemphigus Vulgaris

Background Pemphigus vulgaris is an autoimmune blistering disorder in which autoantibody-mediated loss of keratinocyte adhesion leads to mucosal and cutaneous erosions. Direct immunofluorescence (DIF) is routinely used to confirm the diagnosis by demonstrating intercellular IgG deposition, with or without C3, in a fishnet or chicken-wire pattern. Although DIF is primarily a diagnostic test, its staining intensity and immune-reactant pattern may reflect the burden of tissue-bound immune activity. This study assessed the association between DIF findings and clinical severity in patients with pemphigus vulgaris. Materials and methods This prospective observational study included 60 patients with clinically and histopathologically confirmed pemphigus vulgaris. Clinical severity was assessed at presentation using the pemphigus disease area index (PDAI). DIF was performed on perilesional skin or mucosal biopsy specimens using fluorescein-labelled antisera against IgG, IgA, IgM, C3, and fibrinogen. The type, pattern, and intensity of immune deposits were recorded. DIF intensity was graded semi-quantitatively as 0, 1+, 2+, or 3+. The relationship between DIF intensity and PDAI score was analyzed using Spearman's rank correlation coefficient. Associations between DIF findings and severity categories were assessed using the chi-square test or Fisher's exact test, as appropriate. Results The mean age of the patients was 42.6 ± 13.8 years. There were 34 (56.7%) females and 26 (43.3%) males. Mucocutaneous involvement was the most frequent clinical pattern, observed in 38 (63.3%) patients. Based on PDAI grading, 18 (30.0%) patients had mild disease, 26 (43.3%) had moderate disease, and 16 (26.7%) had severe disease. Intercellular IgG deposition was detected in 58 (96.7%) patients, while combined IgG and C3 deposition was observed in 42 (70.0%) patients. Strong DIF staining was seen more often in patients with severe disease. The mean PDAI score increased across DIF grades, from 11.8 ± 4.3 in patients with weak staining to 45.6 ± 12.1 in those with strong staining. DIF intensity showed a moderate positive correlation with PDAI score (Spearman's rho = 0.62, p < 0.001). Combined IgG and C3 deposition was also significantly associated with moderate-to-severe disease (p = 0.004). Conclusion DIF intensity showed a significant positive association with clinical severity in pemphigus vulgaris. Strong intercellular IgG staining and combined IgG-C3 deposition were more frequent among patients with higher PDAI scores. These findings suggest that semi-quantitative DIF reporting may provide useful supportive information at baseline when interpreted together with clinical severity scoring. However, as this study demonstrates association only, DIF intensity should not be considered an independent predictive or prognostic marker without longitudinal validation.