Juvenile dermatomyositis (JDM) is
a systemic autoimmune disease characterized by chronic skeletal
muscle and cutaneous inflammation of unknown cause.1,2 Symptoms
generally begin before age 18. JDM is relatively responsive to immunosuppressive
therapy, and rapid diagnosis, and institution of adequate therapy
JDM is the most common clinical subset of a larger family of
disorders known as the idiopathic inflammatory myopathies (IIM)
(Table 205-1).1,3,4 Juvenile
polymyositis (JPM), which constitutes 2% to 8% of childhood
myositis cases, has similar features without the characteristic cutaneous
manifestations, but may have more severe and distal weakness. Overlap
myositis, constituting 3% to 10% of childhood
IIM, occurs when JDM or JPM is associated with another autoimmune
disease, such as systemic lupus erythematosus, scleroderma, juvenile
idiopathic arthritis, systemic vasculitis, or type I diabetes mellitus.
JDM and JPM also have been reported in combination with primary
immunodeficiencies such as Wiskott-Aldrich syndrome and common variable
immunodeficiency, without apparent infectious triggers. Other clinical
forms of IIM have been described in children, including dermatomyositis
sine myositis, and focal, orbital, cancer-associated, eosinophilic,
inclusion-body, and granulomatous myositis, but these subsets occur in
fewer than 1 in 1 million children and are not discussed here.
Table 205-1. Clinical Classification
of the Juvenile Idiopathic Inflammatory Myopathies (IIM) |Favorite Table|Download (.pdf)
Table 205-1. Clinical Classification
of the Juvenile Idiopathic Inflammatory Myopathies (IIM)
|Dermatomyositis (JDM)||Characteristic skin rashes of Gottron papules on extensor
surfaces and heliotrope rash over eyelids; may have systemic manifestations
in addition to proximal and axial weakness. Accounts for 85% of juvenile
|Myositis associated with another autoimmune disease (overlap
myositis)||Overlap of myositis with another autoimmune disease. Overlap
with scleroderma most common in children. Seen in 3–10% of
|Polymyositis||Characteristic skin rashes are absent. May have severe weakness. Seen
in 2–8% of juvenile IIM.|
|Amyopathic dermatomyositis||Typical JDM skin rashes without muscle involvement for at
least 2 years’ duration. Rare in children. Rather, mild
muscle inflammation is often present but missed. |
|Focal myositis||Most often presents as an enlarging mass within the affected
muscle, which is usually painful or tender to palpation. The most
common sites of involvement are the thighs and calves, followed
by neck. Case reports in children.|
|Orbital myositis||A form of focal myositis involving the extraocular muscles.
Presents with orbital pain worsened by eye movement. Diplopia,
proptosis, conjunctival injection, periorbital edema, and globe
retraction with narrowing of the palpebral fissure, in the presence
of normal visual acuity, are commonly associated symptoms. Reported
in more than 30 children.|
|Cancer-associated myositis||Myositis develops within two years of a diagnosis of cancer.
Solid organ tumors, lymphoma and leukemia reported. Only a few case reports
in children, mainly with atypical cases of JDM. Routine screening
for malignancy is not routinely performed in the evaluation of children
|Granulomatous myositis||Granulomas prominent in muscle biopsy, often with distal
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