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Juvenile dermatomyositis and polymyositis: Diagnosis

Authors
Clare Hutchinson, MDCM, FRCPC
Brian M Feldman, MD, MSc, FRCPC
Section Editors
Thomas JA Lehman, MD
Marc C Patterson, MD, FRACP
Deputy Editor
Elizabeth TePas, MD, MS

INTRODUCTION

Juvenile dermatomyositis (JDM) and juvenile polymyositis (JPM) are rare autoimmune myopathies affecting children. JDM is characterized primarily as a capillary vasculopathy, whereas JPM involves direct T cell invasion of muscle fibers similar to that seen in adult polymyositis [1,2]. (See "Clinical manifestations of dermatomyositis and polymyositis in adults".)

The diagnosis of JDM and JPM is reviewed here. The pathogenesis, clinical manifestations, and treatment of these disorders are discussed elsewhere. (See "Juvenile dermatomyositis and polymyositis: Epidemiology, pathogenesis, and clinical manifestations" and "Juvenile dermatomyositis and polymyositis: Treatment, complications, and prognosis".)

CLASSIFICATION AND DIAGNOSTIC CRITERIA

The European League Against Rheumatism/American College of Rheumatology (EULAR/ACR) developed and validated revised classification and diagnostic criteria for adult and juvenile idiopathic inflammatory myopathies (IIMs) in 2017 (table 1) [3,4]. These criteria replace the longstanding Bohan and Peter classification schema and diagnostic criteria for the various forms of myositis, including JDM, that were proposed in 1975 [5].

The EULAR/ACR criteria include four variables related to muscle weakness and three related to skin manifestations, as well as variables related to laboratory measurements and other clinical manifestations. Muscle biopsies are infrequently performed in children. Thus, the EULAR/ACR criteria have one scoring system if no muscle biopsy is available and a separate scoring system if the patient has had a muscle biopsy.

The EULAR/ACR score in the absence of a muscle biopsy is interpreted as follows (table 1):

                
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Literature review current through: Nov 2017. | This topic last updated: Nov 28, 2017.
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References
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