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Diagnosis of juvenile dermatomyositis and polymyositis

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 and diagnosis of adult dermatomyositis and polymyositis".)

JDM is the more common of the two disorders accounting for approximately 85 percent of idiopathic inflammatory myopathies of childhood. JPM accounts for only 3 to 6 percent of cases.

The diagnosis of JDM and JPM will be reviewed here. The pathogenesis, clinical manifestations, and treatment of these disorders are discussed elsewhere. (See "Pathogenesis and clinical manifestations of juvenile dermatomyositis and polymyositis" and "Treatment and prognosis of juvenile dermatomyositis and polymyositis".)

CLASSIFICATION AND DIAGNOSTIC CRITERIA

In 1975, Bohan and Peter proposed a classification schema and diagnostic criteria for the various forms of myositis including JDM [3]. Their diagnostic criteria for JDM included all of the following findings [3]:

  • Symmetrical weakness of the proximal muscles
  • Characteristic cutaneous changes, consisting of heliotrope dermatitis (reddish-purple rash on the upper eyelids with periorbital edema) and Gottron's papules (erythematous, papulosquamous eruption over the dorsal surfaces of the knuckles) (picture 1)
  • Elevation of the serum level of one of the muscle enzymes
  • Electromyography (EMG) demonstrating denervation and myopathy
  • Muscle biopsy displaying necrosis and inflammation, as seen in panel A (picture 2)

                

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Literature review current through: Apr 2013. | This topic last updated: Sep 4, 2012.
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