What is dermatomyositis?
Dermatomyositis is an acute inflammatory condition of skin and muscle. There are several distinct types of dermatomyositis which may ultimately prove to be different diseases. Most often dermatomyositis presents with increasing fatigue and loss of proximal (thighs and shoulders) muscle strength accompanied by a heliotrope rash. The characteristic clinical history is simply of a child who is not able to 'keep up', or who is asking to be carried more and more often. Difficulty going up and down stairs is often the manifestation which prompts the family to seek medical attention. These findings may occur with other illnesses, but a careful pediatric rheumatologist can often make the diagnosis on the initial examination. This is because many children have vasculitic lesions of the nail beds ('nailfold capillary dilatation) and lesions of the skin overlying the proximal interphalangeal joints (Gottren's papules). These findings almost invariably signal dermatomyositis or a similar rheumatic disease (scleroderma or progressive systemic sclerosis). Less frequently the onset of dermatomyositis can be rapid with fever, widespread vasculitic rash and profound weakness. Both rapid and gradual onset of disease are often accompanied by a sense of being unwell (malaise) and may be complicated by fever and severe muscle wasting. Laboratory evaluation typically shows elevation of the CPK, SGOT, and aldolase, although in some cases only the CPK or aldolase may be abnormal.
Although not pathologically distinguishable, three distinct patterns of childhood dermatomyositis are clinically recognized. The most common group consists of children with proximal muscle weakness, mild heliotrope rash and no findings suggestive of vasculitis. These children often have a benign illness which resolves over a four to six month period with corticosteroid therapy. In contrast, children with a marked vasculitic rash, or typical findings of vascular involvement in the nail beds (nail-fold capillary abnormalities), or inflammatory papules overlying the interphalangeal joints (Gottren's papules) most often have a more chronic relapsing course. Their disease typically improves with corticosteriod or immunosuppressive therapy, but recurs. Less frequently seen are children with severe rash, markedly elevated muscle enzyme levels, but only moderate weakness. This special subgroup of children is often refractory to therapy and may be an entirely different disease.
Another unusual group of children who may be mistakenly diagnosed as dermatomyositis consists of children who are incidentally found to have markedly elevated CPK levels (e.g. 20,000 units) when being screened for another reason. These children are not weak, do not have a heliotropic rash, and remain well without therapy. Although the precise explanation for this group is unknown, they most likely have a simple biochemical defect. Muscular dystrophy also may present with very high CPK levels, but these children are weak.
What do I have to watch out for?
Vasculitic complications of dermatomyositis can occur in a variety of organs. Mental changes, skin rashes, abdominal pain, and chest infections are all well recognized complications of dermatomyositis which may be associated with severe problems. Arthritis may also complicate dermatomyositis but usually responds to the initiation of corticosteroid therapy.
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