[Dermatomyositis in children]

Dermatomyositis in childhood is an uncommon disease, affecting muscle and skin. The disease usually has an insidious onset; the proximal muscle groups are classically more affected than the distal group. If left untreated, the disease will either spontaneously arrest or will progress until the child is completely bedridden, with death secondary to hypoventilation and aspiration. For a definitive diagnosis 3 or 4 of the following criteria (plus rash) are required: 1) symmetrical limb girdle weakness; 2) muscle biopsy evidence of myositis and muscle necrosis; 3) elevation of muscle enzymes; 4) electromyographic changes of myositis. The main pathologic feature of juvenile dermatomyositis is vasculitis affecting small arteries and veins of muscle, skin and gastrointestinal tract. Whether muscle from patients with polymyositis contains a specific auto antigen or is contaminated with an immunogenic infectious agent such as a virus (coxsackie virus, for instance) remains unclear. Childhood dermatomyositis is almost uniformly responsive to steroid treatment; there is a good chance of remission with minimal risk of secondary complications with an initial low dosage of prednisone (1 mg/kg/day). The use of additional drugs such as azathioprine, methotrexate or cyclophosphamide is reserved for patients who are either not completely responsive to steroids or difficult to wean off steroids. Cyclosporine A has been proposed to achieve a reduction in steroid dosage.