Management of Inflammatory Myositis: Options for Refractory Disease & New Therapies Discussed

Rituximab, cyclophosphamide, repository corticotropin injection (RCI) or other biologic agents are recommended as third-line therapy when patients don’t have a therapeutic response to a second-line treatment.

To assess response to treatment, several outcome measures are important, including disease activity (i.e., global assessments, muscle strength, physical function, lab measures, and extra-skeletal muscle disease activity), damage and quality of life. Improvement in both adults and children is defined as a 20% improvement in three or more of any of the core set of measures, with no more than two worse by 25% or more.

Using a case study, Dr. Lundberg then described how to implement treatment algorithms for refractory inflammatory myositis based on the treatments and response to treatments detailed above. If active disease is found, re-evaluate the diagnosis, she said. If active myositis is confirmed, switch treatment or add another immunosuppressive treatment, biologic or IVIG.

She emphasized the importance of including physical exercise with immunosuppressive treatment, as well as tailoring treatment according to clinical phenotype and serotype.

Overall, Dr. Lundberg underscored the need for new therapies. “Unfortunately, there are few controlled trials in inflammatory myositis and its subgroups, so we lean on case studies and expert opinion,” she said.

Treatment Landscape

Dr. Landon-Cardinal

Océane Landon-Cardinal, MD, FRCPC, a rheumatologist in the Centre Hospitalier de l’Université de Montréal (CHUM) followed with a presentation on emerging therapies and potential novel therapeutic targets. Describing evidence on the key role played by type I interferon in dermatomyositis (DM), she discussed evidence to date from two trials assessing the efficacy of Janus kinase (JAK) inhibitors and toll-like receptor 7/8/9 antagonist in this setting.

One small study suggests that tofacitinib may be effective for patients with DM. At 12 weeks, a minimal to moderate improvement in disease activity was experienced in all 10 subjects according to the 2016 ACR/EULAR myositis response criteria, including a significant improvement on skin disease activity. This improvement was sustained at two years in the extension study.³

Another study looking at the potential of a toll-like receptor 7/8/9 antagonist (IMO-8400) offered less promise, with results showing that this agent conferred no significant difference in skin disease activity compared with placebo in a cohort of 30 patients with DM.⁴

Other agents in the pipeline to treat DM include baricitinib, a JAK inhibitor; PF-06823859, an anti-interferon β monoclonal antibody; apremilast, a PDE-4 inhibitor; abatacept, a T cell co-stimulation blockade; lenabasum, a cannabinoid-2 agonist; tocilizumab, an anti-interleukin (IL) 6 receptor antibody; octagam 10%, a 10% solution of a human intravenous immunoglobulin; and ravulizumab, a complement inhibitor.