Non-targeted immunosuppressive and immunomodulatory therapies for idiopathic inflammatory myopathies.

Background: Idiopathic inflammatory myopathies (IIM) are autoimmune-mediated inflammatory disorders of skeletal muscles with non-muscle involvement in some people, which carry significant morbidity and mortality. Treatment of IIM represents an area of unmet need. This review is an update of a review previously published in 2012, as new and promising data on non-targeted treatments have emerged.

Objectives: To assess the effects (benefits and harms) of non-targeted immunosuppressant and immunomodulatory treatments for IIM: dermatomyositis (DM, including juvenile dermatomyositis, jDM), immune-mediated necrotising myopathy (IMNM), anti-synthetase syndrome (ASS), overlap-myositis (OM) and polymyositis (PM). We also included cancer-related myositis and amyopathic dermatomyositis.

Search methods: On 3 February 2023, we searched the Cochrane Neuromuscular Specialised Register, CENTRAL, Embase, MEDLINE, ClinicalTrials.gov and WHO ICTRP. We intended to check references and citations, and contact experts to identify additional studies, but lacked the resources.

Selection criteria: We included all randomised controlled trials (RCTs) or quasi-RCTs involving participants (adults and children) with IIM according to defined criteria. We included non-targeted immunosuppressants and immunomodulatory treatments alone or in combination, compared with a placebo, no treatment or another non-targeted immunosuppressant or immunomodulatory treatment. Our two primary outcomes were improvement of function or disability and improvement of muscle strength compared with baseline. By preference, we used the Health Assessment Questionnaire Disability Index (HAQ-DI) for disability and the Manual Muscle Test-8 (MMT8) score (adults or children) for muscle strength. Other outcomes were achievement of definitions of improvement (DOI) (the International Myositis Assessment and Clinical Studies (IMACS) Group or the more recent total improvement scores (TIS); for children, we reported achievement of improvement defined by the Paediatric Rheumatology International Trials Organisation (PRINTO)), cumulative corticosteroid dose, change in skin disease activity, serious adverse event and withdrawals for lack of benefit or adverse events.

Data collection and analysis: We followed standard Cochrane methodology. To assess the risk of bias, we used the domain-based Cochrane risk of bias tool (RoB 1). We used fixed-effect models and, when needed, random-effects models for meta-analysis. We created summary of findings tables for any comparison for which data were available but prioritised comparisons of the following with placebo, no treatment or standard care: immunoglobulin, azathioprine and methotrexate. We included other comparisons as additional tables. We assessed the certainty of evidence using the GRADE approach.

Main results: We identified 16 studies (789 participants). The risk of bias in all but one study was high or unclear. Intravenous immunoglobulin (IVIg), compared to placebo, probably improves disability and muscle strength in participants with refractory IIM (standardised mean difference (SMD) 0.86, 95% confidence interval (CI) 0.51 to 1.21 (disability) and 0.78, 95% CI 0.43 to 1.13 (muscle strength); 3 RCTs, 136 participants; both moderate-certainty evidence). IVIg has a higher response rate based on American College of Rheumatology/European League Against Rheumatism (ACR/EULAR) criteria than placebo (risk ratio (RR) 1.80, 95% CI 1.26 to 2.56; 1 RCT, 95 participants; moderate-certainty evidence). IVIg, compared to placebo, improves skin symptoms (Cutaneous Dermatomyositis Disease Area and Severity Index (CDASI) total activity score 0 to 100; higher worse) in people with refractory DM (mean difference (MD) -8.20, 95% CI -11.91 to -4.49; 1 RCT, 95 participants; moderate-certainty evidence). There may be more serious adverse events with IVIg than with placebo (RR 1.91, 95% CI 0.50 to 7.30; 2 RCTs, 144 participants; very low-certainty evidence), but little or no difference between IVIg and placebo in withdrawals for either lack of benefit or adverse events (RR 1.02, 95% CI 0.24 to 4.33; 3 RCTs, 154 participants; very low-certainty evidence). For azathioprine versus placebo, one study showed little or no effect of azathioprine on improvement in muscle strength, but the evidence was very uncertain (RR 1.33, 95% CI 0.43 to 4.13; 1 RCT; 16 participants; very low-certainty evidence). The evidence was also very uncertain for cumulative steroid dose (MD 12.06 mg/kg, 95% CI -6.09 to 30.21; 1 RCT, 16 participants; very low-certainty evidence). This early study did not assess IMACS DOI or CDASI or measure function or disability. Serious adverse events and withdrawals for either lack of benefit or adverse events were not systematically reported. For methotrexate, there may be little or no improvement in adults with DM or PM in function (Amyotrophic Lateral Sclerosis Functional Rating Scale 0 to 40, higher better) (MD 1.24, 95% CI -1.60 to 4.08; 1 RCT, 27 participants; very low-certainty evidence), muscle strength (MMT scale 0 to 80, higher better) (MD -5.68, 95% CI -12.94 to 1.58; 1 RCT, 27 participants; very low-certainty evidence), achievement of IMACS DOI (RR 1.01, 95% CI 0.74 to 1.39; 1 RCT, 27 participants; very low-certainty evidence). Cumulative steroid dose was measured, but the data could not be analysed, and change in CDASI was not measured. In children with new-onset jDM on a background therapy of prednisone, a higher proportion may achieve minimal improvement according to the PRINTO criteria with methotrexate than with placebo (RR 1.40, 95% CI 1.01 to 1.96; 1 RCT, 93 participants; low-certainty evidence). Serious adverse events may occur slightly more frequently with methotrexate (RR 1.48, 95% CI 0.54 to 4.07; 2 RCTs, 124 participants; low-certainty evidence). There may be fewer withdrawals for lack of benefit or adverse events with methotrexate (RR 0.62, 95% CI 0.37 to 1.05; 3 RCTs, 151 participants; low-certainty evidence).

Authors' conclusions: Our review shows improvement in disability, muscle strength and skin symptoms following IVIg in people with refractory DM (for PM, these data are not reliable; other subtypes have not been investigated in RCTs). The improvements related to IVIg in DM may be clinically meaningful, but the absence of established minimal clinically important differences (MCIDs) for both disability and muscle strength in IIM does not facilitate interpretation. For the other agents, the small number of trials of immunosuppressive and immunomodulatory therapies is inadequate to decide whether these agents are beneficial in IIM (excluding IBM). Our review shows room for improvement in the conduct and reporting of clinical trials in IIM, as well as the need to further investigate MCIDs for important outcome measures in IIM.