Childhood onset usually occurs between 5 and 15
years of age. Dermatomyositis in children is similar to the adult form.
However, healing of affected muscles by fibrosis, which may result in
incapacitating contracture deformities (flexion contractures of the ankles
often result in a tiptoe gait), gastrointestinal ulcers, and infections,
seem to be more common in children. Anemia is common as a result of
gastrointestinal ulcerations and hemorrhages. In addition to these
ulcerations with melena and/or hematemesis, extensive bowel infarctions
caused by necrotizing arteritis can complicate the course of the disease.
Progressive weakness of proximal muscles is present, usually in combination
with elevated serum levels of creatinine phosphokinase (not mandatory),
transaminases (aspartate aminotransferase [ASAT], alanine aminotransferase
[ALAT]), lactate dehydrogenase, and aldolase. Results of EMG
are abnormal. The degree of weakness can range from mild to severe, and even
quadriparesis has been reported. Weakness of swallowing musculature
(dysphagia), intercostal muscles, and the diaphragm may lead to problems
with airway protection and respiration (10% of cases). Myocardial
fibrosis can cause arrhythmias (heart block), ventricular dysfunction
(dilated cardiomyopathy), and heart failure. Interstitial lung disease may
be present and usually is mild (these patients often are anti-Jo-1 antibody
[a myositis-specific antibody] positive). Use of steroids has improved
mortality but with the expense of inherent problems of steroid therapy.
Additional immunosuppressive drugs may be needed. A negative nitrogen
balance is present when the disease is active. Sensation is not altered, and
tendon reflexes are preserved unless the muscle strength is severely
compromised by the inflammatory process. Death usually results from
respiratory failure, heart failure, or a complicating infection. Up to
20% of adult cases (especially when the rash is present and the age of
onset is late) are associated with occult neoplasms (lung, breast, ovary,
stomach, prostate, nonmelanoma skin cancer), and dermatomyositis is
considered a paraneoplastic syndrome in these patients. Steroids,
salicylates, and immunosuppressives (azathioprine, cyclophosphamide,
intravenous immunoglobulins) are used to suppress the inflammatory process.
Subcutaneous calcifications can cause skin ulcerations and infections when
they protrude through the skin.