Low-dose rituximab is efficacious in refractory idiopathic inflammatory myopathies

Rituximab (RTX) 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.

Registry-based observational data about IIM patients receiving RTX between 2018 and 2021 were included. Total improvement score was calculated from the core set measures as per International Myositis Assessment and Clinical Studies group (IMACS) at baseline, 6 months and 12 months of follow-up.

Forty-two patients (F:M, 29:13), with a mean (s.d.) age of 39.5 (11.5) years were studied. Majority of patients received RTX for refractory myositis, after a median (interquartile range) duration of 8 (4,18) months. Twenty-eight received RTX at a dosage of 1 g × two doses, while 14 received 500 mg × two 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, physician global assessment (PGA), patient global assessment (PtGA) and median steroid dosage as compared with the baseline (P < 0.01 for all). A mean (s.d.) improvement of 44.5 (16) and 48.7 (19.2) in total improvement score was recorded at 6 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 and 12 months. Severe lower respiratory tract infections requiring hospitalization occurred in three patients of the cohort.

RTX 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 two doses of 500 mg can be as efficacious as 1 g at 6 months and 12 months of follow-up.