Correlation of Antimuscarinic Acetylcholine Receptor Antibody Titers With Pemphigus Disease Activity at Baseline and Following Phase I Pulse Therapy.

Background Pemphigus is a rare autoimmune blistering disorder characterized by involvement of the skin and mucous membranes, primarily due to autoantibodies targeting desmogleins. Emerging evidence has pointed to a potential pathogenic role of antimuscarinic acetylcholine receptor (anti-M-AChR) antibodies and reported a correlation between their titers and pemphigus disease activity. However, data on this association, particularly in relation to different phases of pulse therapy in the Indian context, remain limited. Aim This study aimed to evaluate the correlation between anti-M-AChR antibody titers and pemphigus disease activity at baseline and after Phase I of dexamethasone-cyclophosphamide/azathioprine pulse therapy. Materials and methods This prospective longitudinal observational study included newly diagnosed cases of pemphigus confirmed through histopathology and direct immunofluorescence from April 2019 to March 2021. Pemphigus Disease Area Index (PDAI) scores were recorded, and eligible patients received dexamethasone-cyclophosphamide or dexamethasone-azathioprine pulse therapy as appropriate. Results A total of 29 patients were enrolled: 23 (79%) with pemphigus vulgaris, five (17%) with pemphigus foliaceus, and one (3.4%) with pemphigus erythematosus. Patient ages ranged from 21 to 69 years, with a male-to-female ratio of 0.7:1. By the end of Phase I therapy, 20 patients (69%) completed follow-up. The mean baseline anti-M-AChR antibody titer was 76.48 ± 48.12 U/mL, which decreased to 53.61 ± 30.97 U/mL after Phase I. At that point, PDAI scores showed a moderate correlation with anti-M-AChR antibody levels (r = 0.51, p = 0.02). The reduction in antibody titers from baseline to the end of Phase I was statistically significant (p = 0.05). Conclusions While serum anti-M-AChR antibody titers may not reliably indicate disease activity at the time of diagnosis, their levels appear to reflect changes in disease activity following treatment. This suggests their potential use as a prognostic marker during the course of therapy.