Rituximab in myositis: where are we now? A survey of current usage

Dear Editor, In a retrospective analysis 7 years ago, it was estimated that ∼78% of patients with inflammatory myositis were considered to have improved with rituximab (RTX) [1]. The International Myositis Assessment & Clinical Studies (IMACS) group felt it was timely to undertake a prospective study of the use of RTX in myositis. Members of the group were invited to send information about RTX-treated patients from July 2021 during the following year. After lengthy discussions, a simple proforma was produced and sent to the IMACS members on four occasions during the year. The key aims of the study were to: assess the current use of B cell depletion in patients with myositis; obtain background information about which particular patients are being treated in this way; and ascertain if B cell depletion continues to be effective in myositis. Fifty myositis patients from nine referring centres were distinguished in two groups based on the time of first RTX infusion (29 had been prescribed it before July 2021, designated previous users, and 21 were new starters). The patients’ demographic features, characteristics of myositis and treatment response are summarized in Table 1. The median time from the diagnosis until the first RTX infusion was 21.5 months (interquartile range = 65). Most were females (74%), of Caucasian origin (56%) and had a diagnosis of anti-synthetase syndrome (56%). Three out of 50 patients were myositis-specific antibody (MSA) negative. The most common immunosuppressive agent used with RTX was CS (84%), followed by MMF (36%), MTX (10%), AZA (8%), CSA (8%) and CYC (2%). RTX was preferred as a first line drug with steroids in five patients (two were reported to have responded well). Effectiveness was assessed by the treating physician on the basis of clinical observation, reduction in the creatine kinase and capacity to reduce steroids. Based on these components, RTX was reported to be effective in 43 patients (86%), and no benefit was seen in 7 patients (14%). Treatment response was found to be similar in both groups (89.7% vs 81%, P = 0.434). Of note, no statistically significant difference was seen in RTX effectiveness among types of myositis (anti-synthetase syndrome vs others), MSAs and genders. Steroid taper was successfully achieved in 78.7% of patients. Adverse events were noted in seven patients; all were infectious complications with requirement for hospitalization in three cases. Three minor side effects including two infusion reactions and one nausea were reported during the entire follow-up.