Abstract
Juvenile Dermatomyositis (JDM) is a systemic immune-mediated disease of childhood, characterized by muscle weakness, and a typical skin rash. Other organ systems and tissues such as the lungs, heart, and intestines can be involved, but may be under-evaluated. The inflammatory process in JDM is characterized by an interferon signature and infiltration of immune cells such as T cells and plasmacytoid dendritic cells into the affected tissues. Vasculopathy due to loss and dysfunction of endothelial cells as a result of the inflammation is thought to underlie the symptoms in most organs and tissues. JDM is a heterogeneous disease, and several disease phenotypes, each with a varying combination of affected tissues and organs, are linked to the presence of myositis autoantibodies. These autoantibodies have therefore been extensively studied as biomarkers for the disease phenotype and its associated prognosis. Next to identifying the JDM phenotype, monitoring of disease activity and disease-inflicted damage not only in muscle and skin, but also in other organs and tissues, is an important part of clinical follow-up, as these are key determinants for the long-term outcomes of patients. Various monitoring tools are currently available, among which clinical assessment, histopathological investigation of muscle and skin biopsies, and laboratory testing of blood for specific biomarkers. These investigations also give novel insights into the underlying immunological processes that drive inflammation in JDM and suggest a strong link between the interferon signature and vasculopathy. New tools are being developed in the quest for minimally invasive, but sensitive and specific diagnostic methods that correlate well with clinical symptoms or reflect local, low-grade inflammation. In this review we will discuss the types of (extra)muscular tissue inflammation in JDM and their relation to vasculopathic changes, critically assess the available diagnostic methods including myositis autoantibodies and newly identified biomarkers, and reflect on the immunopathogenic implications of identified markers.
Highlights
Juvenile Dermatomyositis (JDM) is a systemic immune-mediated disease of childhood
JDM is characterized by inflammation of skeletal muscles and skin, leading to muscle weakness and a typical skin rash of the face and hands, which are used as classification criteria [6, 7]
Up to 75% of children with JDM develop respiratory involvement, which may result from a complication of respiratory muscle weakness or immunosuppressive therapy, or from interstitial lung disease (ILD) [25, 26]
Summary
Juvenile Dermatomyositis (JDM) is a systemic immune-mediated disease of childhood. It is the most common idiopathic inflammatory myopathy in children, with an incidence of 2– 4/million/year [1]. The pathologic changes underlying symptoms and tissue damage in the skin, muscles, and vital organs have a common factor: in all the affected tissues typical vasculopathic changes are observed, which include loss of capillaries (capillary dropout), perivascular inflammation, and (occlusive) small vessel angiopathy [21, 45]. The presence of prominent vascular injury in muscle biopsies identified a subgroup of patients with more severe clinical presentation and outcomes, including profound muscle weakness, limb edema and gastrointestinal involvement [55] This suggests that local vasculopathic changes can reflect systemic vasculopathy and the resulting clinical symptoms. Common symptoms in Caucasian patients with anti-MDA5 antibodies include oral and cutaneous ulceration, arthritis, and milder muscle disease with fewer histologic abnormalities and a higher remission rate off medication after 2 years of follow-up [76, 82, 84, 85]. Activated plasmacytoid dendritic cells (pDC) are generally thought to be the main producers of the type 1 IFNs
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