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Dermatomyositis (DM) is a rare and debilitating, systemic, autoimmune disease. While heterogenous in presentation and severity, DM is primarily characterised by a spectrum of skin and muscle disease, which may include proximal muscle weakness and recalcitrant cutaneous eruptions. DM may also be associated with joint pain and stiffness, inflammatory arthritis, dysphagia, fatigue, and calcinosis. The current standard of care for DM includes glucocorticoids, immunosuppressants, and intravenous immunoglobulin (IVIg). Unfortunately, these medications are not uniformly effective and can lead to adverse events, particularly with chronic use, necessitating discontinuation of therapy. Therefore, a substantial unmet need exists for more tailored and efficacious therapies that target DM pathogenesis. Brepocitinib is an oral, once-daily, novel, and specific TYK2/JAK1 inhibitor. Brepocitinib's potent inhibition of TYK2 and JAK1 reduces the signalling of pro-inflammatory cytokines, including IFN-α/β, IL-12, IL-23, and IFNγ, that have been implicated in the pathogenesis of DM. Other JAK inhibitors have been used off-label in both case series and open-label clinical trials in patients with DM; and brepocitinib has demonstrated efficacy in phase 2 clinical trials of several other autoimmune diseases, including plaque psoriasis, psoriatic arthritis, Crohn's disease, hidradenitis suppurativa, and ulcerative colitis. Therefore, there is a strong scientific and clinical rationale for the utility and potential effectiveness of brepocitinib in the treatment of DM patients. Currently, the safety, tolerability, and efficacy of brepocitinib is being evaluated in the largest (n=225) double-blind placebo-controlled phase 3 trial in DM patients to date (VALOR - NCT0543726).

Dermatomyositis (DM) is an idiopathic inflammatory myopathy that commonly manifests with proximal muscle weakness and is associated with extramuscular pathology, including characteristic skin lesions such as Gottron's papules and heliotrope rash, as well as lung, gastrointestinal, joint, and cardiac involvement. Systemic corticosteroids are a cornerstone of therapy, and more recently intravenous immunoglobulin (IVIG; OCTAGAM®) has been approved by the US Food and Drug Administration for the treatment of adults with DM. Both steroids and IVIG represent nonspecific anti-inflammatory therapy, and more targeted approaches are lacking. Transcriptomics has identified upregulation of interferon (IFN)-regulated genes as key features of both adult DM and juvenile DM (JDM). Accordingly, blocking IFN signalling through inhibition of the Janus kinase (JAK) pathway represents a potential treatment option for DM. Placebo-controlled trial data assessing the use of JAK inhibitors for the treatment of DM are limited; as such, a systematic literature review was undertaken to assess the evidence of JAK inhibitors in the treatment of patients with DM. Terms related to DM and JAK inhibitors were searched using PubMed, Embase, Web of Science, Scopus, and Dimensions to identify peer-reviewed publications reporting patients with DM who were treated with a JAK inhibitor. Baseline demographics, clinical characteristics, and treatment outcome data were extracted. A total of 48 publications reporting 145 unique patients (adult DM, n=84; JDM, n=61) were identified. Among cases of adult DM, 61 of 84 (73%) had refractory skin disease at baseline, and all (61 of 61) reported improvement in cutaneous symptoms. Of patients with adult DM, 16 of 84 (19%) had refractory muscle disease at baseline, and all (16 of 16) reported improvement in muscle symptoms. In patients with adult DM complicated by interstitial lung disease (ILD; n=33), 31 (94%) patients improved with JAK inhibitor treatment. Among cases of JDM with refractory skin disease at baseline (60 of 61), most patients (57 of 60; 95%) showed improvements in skin symptoms after JAK inhibitor treatment. Of patients with JDM with refractory muscle disease at baseline (36 of 61), most (30 of 36; 83%) reported improvement in muscle symptoms. Four patients with JDM and ILD experienced improvement in lung disease activity following treatment with a JAK inhibitor. Among both DM and JDM cases, all patients (17 with DM and 16 with JDM) who had elevated serum IFN and/or IFN-stimulated gene expression at baseline showed reduction in IFN or IFN gene expression. Although the conclusions that can be drawn from this analysis are limited because of the differences in assessments used across publications, overall treatment of patients with DM or JDM with a JAK inhibitor was associated with significant improvement of a wide range of DM manifestations, including skin lesions, muscle weakness, and ILD. Our systematic literature review suggests that JAK inhibitors may be a viable treatment option for DM/JDM, and randomised controlled trials are necessary to confirm these findings.