LAUSR

OBJECTIVES Rituximab use early in the course of refractory idiopathic inflammatory myopathy(IIM) is not well studied. This study sought to determine the short-term efficacy of RTX in a registry based cohort of refractory IIM. METHODS Registry based observational data about IIM patients receiving rituximab(RTX) between 2018-2021 were included. Total improvement score(TIS) was calculated from the core set measures as per IMACS at baseline, 6 months and 12 months of follow-up. RESULTS Forty two patients (F: M::29:13), with a mean(SD) age of 39.5(±11.5) years were studied. Majority of patients received rituximab for refractory myositis, after a median(IQR) duration of 8(4,18) months. Twenty-eight received RTX at a dosage of 1 gram *2 doses, while 14 received 500 mg * 2 doses with an interval of 15 days.At 6 months and 12 months post RTX, the improvement was recorded in manual muscle testing(MMT-8) scores, PGA(physician global assessment), PtGA(patient global assessment), median steroid dosage as compared with the baseline (p< 0.01 for all). A mean(SD) improvement of 44.5 ± 16 and 48.7 ± 19.2 in TIS was recorded at 6 months and 12 months respectively. The change in MMT-8, PGA and PtGA scores from baseline between the two dosage regimens of RTX were comparable at 6 months and 12 months. Severe lower respiratory tract infections requiring hospitalisation occurred in 3 patients of the cohort. CONCLUSION Rituximab improved IMACS core set measures and had steroid sparing efficacy at 6 and 12 months in patients with IIM in this registry-based study. Rituximab as an induction regimen of 2 doses of 500 mg can be as efficacious as 1 g at 6 months and 12 months of follow-up.