A systematic review on biological therapies in juvenile idiopathic inflammatory myopathies: an evidence gap in precision medicine

Objective Juvenile idiopathic inflammatory myopathies (JIIMs) are a heterogeneous group of systemic autoimmune diseases. Juvenile dermatomyositis (JDM) is the predominant form of JIIMs, and is a rare, chronic autoimmune illness characterised by symmetric, proximal muscle damages and involvement of the skin. In the last two decades, the use of monoclonal antibodies has also been expanded to JIIMs; however, there is limited evidence on use of these treatments. We assessed the efficacy/effectiveness and safety of biologic agents in JIIMs. Methods A systematic literature review was conducted using Embase (R), MEDLINE (R), MEDLINE (R)-In Process and Cochrane library to identify studies on biologics agents in JIIMs published in English language as full-text articles (1975 to December 2020) or conference abstracts (2000 to December 2020). Databases were searched with the key words regarding chronic myositis crossed with "biologic agents OR tocilizumab OR rituximab OR adalimumab OR infliximab OR anti-TNF OR etanercept". Of note, we did not include children, age, or age limits in the search as medical subject headings terms because we may have been able to extract a sub cohort of children from studies including both children and adults. Results Of the 1633 retrieved publications, 18 articles were identified for a total of 165 patients. In real-world studies, definition of complete (CR) or partial response (PR) varied. JIIMs patients were most often treated with anti-TNF (88 pts); patients received etanercept (ETA), 48 patients infliximab (IFX), 4 patients received adalimumab (ADA). In other 15 patients IFX was followed by ADA. Rituximab (RTX) was used in 73 children. A single case series reported the use of abatacept (ABA) in 4 patients. Despite the reduced number of treated patients, complete response on myositis was reported in 29.6% (8/26) patients treated with at least one anti-TNF and in 38% (10/26) treated by RTX. Complete response of skin vasculitis has been reached in 33% (4/12) children on anti-TNF and in 36% on RTX (21/58). Anti-TNF agents might be efficient in treating calcinosis lesions. Conclusion Currently, the available evidence regarding the use of biologic treatment in JIIMs results quite limited but suggest a promising the use of anti-TNF agents and RTX in treating active JIIMs. Anti-TNF treatment might have a role in treating calcinosis. However, an overall very low quality of the available studies and multiple confounding factors hamper to suggest a treatment over another. Thus, randomised clinical trials are urgently required to attempt the optimal treatment in real-world setting.