Comparing the Efficacy of Conventional Immunosuppression and Rituximab in Anti-SRP Myositis: Insights from a Tertiary Care Centre Experience

Background Consensus on anti-SRP myositis shows that early rituximab (RTX) is favoured over conventional immunosuppression (cIS), but the data is derived from case series without comparative studies. This study aims to a) explore poor prognostic features, and b) assess and compare the efficacy and safety of RTX with cIS in individuals with anti-SRP myositis. Methods This is an observational study in a tertiary care centre in India. Data was obtained from a prospectively maintained database comprising consecutive adult (> 16 years) patients diagnosed myositis. A total of 1033 myositis patients were screened from January 2019 to January 2024. Fourty IIM patients with confirmed anti-SRP positivity fulfilling inclusion criteria with more than 3 months of follow-up were selected for the study and response analysis. Details were obtained at baseline, 3 months, and 6 months, as well as subsequent follow-up. Treatment response was categorised as improved, worsening, or stable disease. The characteristics of patients between “RTX” and “cIS” groups were compared using t-test and Chi-square test as appropriate. Survival analysis curves were plotted for improvement and death between the two groups. Results The mean age of onset of anti-SRP myositis was 44.2 (SD13.14) years; 71.4% of patients were female. Baseline characteristics are described in Table 1. For response analysis, 35 patients into two groups: RTX and cIS. Fifteen (42.85%) patients were given RTX. While 20 received cIS (57.14%, 12/20 (60%) received mycophenolate mofetil, 8/20 (40%) received methotrexate, and 5/20 (25%) received cyclophosphamide). The median follow-up was 12 (IQR 6-24) months. There was no significant difference in improvement between RTX and cIS groups (11/15 (73.3%) RTX group and 9/20(45%) cIS group (p-value -0.465)). Time to improvement was also not significantly different (Figure 1). However, the Mean change in MMT8 from baseline to 6 months was more in the RTX group (p-value 0.001). The average monthly steroid dose significantly decreased six months after RTX with a p-value of 0.001(1600.13mg (SD 271.53) in RTX versus 826.6 mg (SD 370.35) in cIS). Mortality rates stood at 1/15 (6.67%) for RTX and 4/20 (20%) for cIS. Unravelling predictors of mortality revealed significant associations with cardiac involvement (p-value - 0.02) and severe non-ambulant muscle weakness (p-value - 0.03). Conclusions Both cIS and RTX are effective and safe in anti-SRP myositis for muscle affection and time f