Clinical and immunological predictors of post-rituximab paradoxical pemphigus flare: A prospective cohort study

Background Paradoxical flare of pemphigus following rituximab infusion has been reported previously, however, its incidence or risk factors have not been studied in detail. Objectives To evaluate the clinical and immunological predictors associated with post-rituximab paradoxical pemphigus flare. Materials and Methods This was a prospective cohort study including adult patients with pemphigus vulgaris or foliaceus who were treated with rituximab. Patients were administered 1000 mg of intravenous rituximab on days 0 and 14 (Rheumatoid arthritis (RA) protocol), with or without oral prednisolone and/or conventional immunosuppressive agents. Baseline clinical and immunological predictors of post-rituximab pemphigus flares were assessed. Results Fifty patients (mean age 40.44 ± 12.36 years) with a mean pemphigus disease area index (PDAI) score of 27.8 ± 15.48 were administered rituximab. Post-rituximab flare occurred in 10 (20%) patients after a mean of 14.1 ± 4.33 days after the first rituximab infusion. The mean baseline PDAI score (36.4 ± 11.7 vs. 25.6 ± 15.7, P = 0.02) and serum anti-Dsg1 levels (1216.8 ± 850.1 vs. 592 ± 562.12 RU/mL, P = 0.03) were statistically significantly higher in patients experiencing a flare. Using ROC-curve analysis, a PDAI score of ≥28 (OR 8.3, 95% CI 1.5-44.7) was 80% sensitive and 67.5% specific in predicting post-rituximab flare, while serum anti-Dsg1 level of ≥1137.78 RU/ml had a sensitivity of 60% and specificity of 85%. There was no significant difference in terms of affected body surface area, type of pemphigus, starting prednisolone dose, oral immunosuppressive adjuvant, serum anti-Dsg3, serum anti-AchRM3, and peripheral CD19+ B cell population. Limitations Our study is limited by a relatively small sample size. Immunological factors were not evaluated at the time of pemphigus flare. Though these unexpected pemphigus flares are likely to be associated with rituximab infusion, the possibility of spontaneous disease exacerbation cannot be entirely excluded. Conclusions Patients with more severe pemphigus or high serum anti-Dsg1 are at risk of post-rituximab paradoxical flare, and may benefit from rituximab administration under close monitoring.