Pathogenesis and clinical manifestations of juvenile dermatomyositis and polymyositis
- 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]. (See "Clinical manifestations of dermatomyositis and polymyositis in adults".)
The epidemiology, pathogenesis, and clinical manifestations of JDM and JPM will be reviewed here. Diagnosis and treatment of these disorders are discussed elsewhere. (See "Diagnosis of juvenile dermatomyositis and polymyositis" and "Treatment and prognosis of juvenile dermatomyositis and polymyositis".)
Juvenile dermatomyositis (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].
Juvenile polymyositis (JPM) occurs less frequently and accounts for only 3 to 6 percent of childhood idiopathic inflammatory myopathies [3,7].
Although the etiology remains unclear, it has been proposed that juvenile dermatomyositis (JDM) and juvenile polymyositis (JPM) are caused by an autoimmune reaction in genetically susceptible individuals, possibly in response to environmental triggers.
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- Genetic susceptibility
- Immunologic mechanisms
- CLINICAL MANIFESTATIONS
- Cutaneous manifestations
- - Rash
- - Nailfold capillary changes
- - Skin ulcerations
- - Calcinosis
- - Amyopathic dermatomyositis
- Muscle weakness
- Other findings