Juvenile dermatomyositis and polymyositis: Epidemiology, pathogenesis, and clinical manifestations
- Clare Hutchinson, MDCM, FRCPC
Clare Hutchinson, MDCM, FRCPC
- Pediatric Rheumatologist
- University of Toronto
- Brian M Feldman, MD, MSc, FRCPC
Brian M Feldman, MD, MSc, FRCPC
- Professor of Pediatrics
- University of Toronto
- Section Editors
- Thomas JA Lehman, MD
Thomas JA Lehman, MD
- Section Editor — Pediatric Rheumatology
- Professor of Clinical Pediatrics
- Cornell University Medical College
- Marc C Patterson, MD, FRACP
Marc C Patterson, MD, FRACP
- Section Editor — Pediatric Neurology
- Professor of Neurology, Pediatrics, and Medical Genetics
- Chair, Division of Child and Adolescent Neurology
- Mayo Clinic College of Medicine
Juvenile dermatomyositis (JDM) and juvenile polymyositis (JPM) are rare autoimmune myopathies in childhood. JDM is primarily a capillary vasculopathy, whereas JPM involves direct T cell invasion of muscle fibers similar to that seen in adult polymyositis (PM) [1,2]. However, as the diagnostic tools become more sophisticated (eg, biopsies that demonstrate inclusion body myositis or inflammatory dystrophies, or autoantibodies that are markers of particular types of myositis such as anti-signal recognition particle [SRP] and necrotizing myopathy), fewer patients are diagnosed with JPM, calling into question whether JPM is a specific entity. (See "Clinical manifestations of dermatomyositis and polymyositis in adults".)
The epidemiology, pathogenesis, and clinical manifestations of JDM and JPM are reviewed here. Diagnosis and treatment of these disorders are discussed elsewhere. (See "Juvenile dermatomyositis and polymyositis: Diagnosis" and "Juvenile dermatomyositis and polymyositis: Treatment, complications, and prognosis".)
JDM is the most common idiopathic inflammatory myopathy of childhood, accounting for approximately 85 percent of cases [3,4]. In population-based studies, JDM has a reported annual incidence that ranges from two to four cases per one million children [5-9]. The peak incidence is from 5 to 10 years of age [8,9]. Girls are affected more often than boys, with a two- to fivefold greater rate [7,8,10].
JPM occurs less frequently and accounts for only 3 to 6 percent of childhood idiopathic inflammatory myopathies [3,7].
JDM and JPM are thought to be autoimmune disorders. JDM is associated with systemic vasculopathy. It is sometimes associated with occlusive arteriopathy and capillary necrosis that eventually lead to capillary loss and tissue ischemia. Although the etiology remains unclear, it has been proposed that JDM and JPM are caused by an autoimmune reaction in genetically susceptible individuals, possibly in response to infection or environmental triggers such as prenatal exposure to tobacco smoke and particulate inhalants .
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- Genetic susceptibility
- Immunologic mechanisms
- CLINICAL MANIFESTATIONS
- Muscle weakness
- Cutaneous manifestations
- - Heliotrope rash
- - Gottron's papules
- - Nailfold capillary changes
- - Skin ulcerations
- Pulmonary involvement
- Gastrointestinal vasculopathy
- LABORATORY FINDINGS