Juvenile myositis / juvenile polymyositis / juvenile dermatomyositis
Overview
Juvenile myositis (JM) refers to a group of rare autoimmune diseases that cause chronic muscle inflammation and weakness in children. There are two primary subtypes:
- juvenile dermatomyositis (JDM)
- juvenile polymyositis (JPM)
Both are officially classified as autoimmune diseases due to the presence of autoantibodies, immune cell infiltration into muscle tissue, and a strong response to immunosuppressive therapy. In these conditions, the immune system mistakenly targets the child’s muscle fibers (and in JDM, also the skin), resulting in inflammation and tissue damage.
Common Symptoms
Muscle weakness, fatigue, difficulty climbing stairs or lifting objects, muscle pain, rash (especially on knuckles, eyelids, or face in JDM), calcinosis (calcium deposits under the skin), joint pain, difficulty swallowing, fever.
Coexisting Diseases and Conditions
Lupus, scleroderma, Hashimoto’s thyroiditis, interstitial lung disease, vasculitis, or gastrointestinal complications.
Risk Factors and Prevalence
Juvenile myositis is a very rare condition, with juvenile dermatomyositis (JDM) affecting approximately 2 to 4 children per million each year in the United States. Juvenile polymyositis (JPM) is even more uncommon and may be subject to overdiagnosis due to overlap syndromes or misclassification. This disease typically manifests between the ages of 5 and 10 and is diagnosed more frequently in girls.
The exact cause of juvenile myositis remains unclear, but it is thought to arise from a combination of genetic factors and environmental triggers. Suspected triggers include:
- Viral infections
- Ultraviolet (UV) light exposure
- Certain medications or vaccines (in rare cases, temporally associated)
- Stressful immune challenges, such as surgery or trauma
Recent Research
- Juvenile Dermatomyositis: Updates in Pathogenesis and Biomarkers, Current Treatment, and Emerging Targeted Therapies (2025)
- Juvenile Dermatomyositis and Hepatitis B Viral Infection (2025)
- The Characteristics and Risk Factors of Cytomegalovirus Infection in Dermatomyositis (2025)
- Cancer and myositis: Who, when, and how to screen (2022)
- Benign acute childhood myositis: our experience on clinical evaluation (2022)
- Prospective, double-blind, randomized, placebo-controlled phase III study evaluating efficacy and safety of octagam 10% in patients with dermatomyositis (“ProDERM Study”) (2021)
Sources
- Sources
Kim, H., Huber, A. M., & Kim, S. (2021). Updates on Juvenile Dermatomyositis from the Last Decade: Classification to Outcomes. Rheumatic diseases clinics of North America, 47(4), 669–690. https://doi.org/10.1016/j.rdc.2021.07.003
Kobayashi I. (2024). Advances in Juvenile Dermatomyositis: Pathophysiology, Diagnosis, Treatment and Interstitial Lung Diseases-A Narrative Review. Children (Basel, Switzerland), 11(9), 1046. https://doi.org/10.3390/children11091046
Kim, H. Juvenile Dermatomyositis: Updates in Pathogenesis and Biomarkers, Current Treatment, and Emerging Targeted Therapies. Pediatr Drugs 27, 57–72 (2025). https://doi.org/10.1007/s40272-024-00658-2
Wu, J. Q., Lu, M. P., & Reed, A. M. (2020). Juvenile dermatomyositis: advances in clinical presentation, myositis-specific antibodies and treatment. World journal of pediatrics : WJP, 16(1), 31–43. https://doi.org/10.1007/s12519-019-00313-8
Rider, L. G., et al. (2011). Measures of adult and juvenile dermatomyositis, polymyositis, and inclusion body myositis: Physician and Patient/Parent Global Activity, Manual Muscle Testing (MMT), Health Assessment Questionnaire (HAQ)/Childhood Health Assessment Questionnaire (C-HAQ), Childhood Myositis Assessment Scale (CMAS), Myositis Disease Activity Assessment Tool (MDAAT), Disease Activity Score (DAS), Short Form 36 (SF-36), Child Health Questionnaire (CHQ), physician global damage, Myositis Damage Index (MDI), Quantitative Muscle Testing (QMT), Myositis Functional Index-2 (FI-2), Myositis Activities Profile (MAP), Inclusion Body Myositis Functional Rating Scale (IBMFRS), Cutaneous Dermatomyositis Disease Area and Severity Index (CDASI), Cutaneous Assessment Tool (CAT), Dermatomyositis Skin Severity Index (DSSI), Skindex, and Dermatology Life Quality Index (DLQI). Arthritis care & research, 63 Suppl 11(0 11), S118–S157. https://doi.org/10.1002/acr.20532
Li, D., & Tansley, S. L. (2019). Juvenile Dermatomyositis-Clinical Phenotypes. Current rheumatology reports, 21(12), 74. https://doi.org/10.1007/s11926-019-0871-4
DeWane, M. E., Waldman, R., & Lu, J. (2020). Dermatomyositis: Clinical features and pathogenesis. Journal of the American Academy of Dermatology, 82(2), 267–281. https://doi.org/10.1016/j.jaad.2019.06.1309
Betteridge, Z., & McHugh, N. (2016). Myositis-specific autoantibodies: an important tool to support diagnosis of myositis. Journal of internal medicine, 280(1), 8–23. https://doi.org/10.1111/joim.12451