Exercise in action for JUVENILE DERMATOMYOSITIS : Steps towards understanding

This thesis describes studies in the field of juvenile dermatomyositis (JDM), a chronic inflammatory disease in which the microvasculature is attacked by the immune system. Clinical characteristics include symptoms of muscles (e.g. weakness) and skin (e.g. Gottron’s papules over the extensor joint surfaces, heliotrope rash over the eyelids, and photosensitivity). The objectives of the studies in this rare disease were: A) to gain a better understanding of the exercise intolerance and fatigue; B) to contribute to an improvement in the prognostics and monitoring of disease course; and C) to examine the feasibility, safety, and efficacy of exercise training. In a cross-sectional study, the oxygenation and hemodynamics during exercise and recovery were assessed in children with JDM with near-infrared spectroscopy and compared with results from children in juvenile idiopathic arthritis as well as healthy controls. Patients with JDM showed lower values of total hemoglobin in the vastus medialis muscle during the whole exercise test compared to healthy children, whereas the results in patients with juvenile idiopathic arthritis were similar to those in healthy controls. In collaboration with groups in North-America and Canada, we examined the association of factors available at disease onset for their association with disease course in a large cohort (n=365) of patients with juvenile idiopathic inflammatory myopathies (JIIM), including JDM. These factors included demographics, clinical features present prior to diagnosis, the highest recorded serum muscle enzyme levels, myositis autoantibodies, environmental factors at illness onset and at diagnosis, and immunogenetic polymorphisms. By univariable and multivariable approaches, we determined myositis-specific and -associated autoantibodies, specifically the anti-p155/140 and anti-Ro autoantibodies, and a number of clinical features, and environmental exposures present at disease onset or diagnosis that were associated with a chronic disease course in patients with JIIM. In a small cohort of patients with JDM, the opportunities of non-invasive, quantitative muscle ultrasonography in the longitudinal follow-up were explored together with clinical variables. The findings of this study indicate that ultrasonography provides additional information in the follow-up of patients with JDM regarding disease activity, fibrosis, and atrophy, particularly after normalisation of the Childhood Myositis Assessment Scale. In a systematic review, the efficacy and safety of exercise training in juvenile and adult idiopathic inflammatory myopathies (including JDM) were examined. Exercise training appeared to be safe and effective in adult patients with idiopathic inflammatory myopathies in active as well as inactive disease, although most of the included studies had a high selection and/or allocation bias. Recently, two studies on exercise training in children with JDM were published. These studies indicate positive effects of exercise training in this group. However, both studies had a small sample size and were uncontrolled. In a randomized controlled trial, the feasibility, safety, and efficacy of a home-based exercise training program in patients with JDM were evaluated. The individually tailored 12-week home-based exercise training program was feasible in most patients, safe in all patients, and effective for aerobic fitness, muscle function, and functional ability. Therefore, exercise training is of additional value in the clinical management of patients with JDM.

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