Dermatomyositis
Introduction
Dermatomyositis (DM) is one of the idiopathic inflammatory myopathies.1, 2, 3 In 1975, Bohan and Peter4 published a classic article that suggested a set of criteria to aid in the diagnosis and classification of DM and polymyositis (PM). Of the 5 criteria, 4 related to the muscle disease: (1) progressive proximal symmetrical weakness, (2) elevated muscles enzymes, (3) an abnormal electromyogram, and (4) an abnormal muscle biopsy, while the fifth was the presence of compatible cutaneous disease. It was felt that DM differed from PM only by the presence of cutaneous disease. Recent studies of the pathogenesis of the myopathy have been controversial, some suggesting that the myopathies in DM and PM are pathogenetically different with DM being due to a vascular inflammation,5 whereas other studies of cytokines suggest that the processes are similar.6, 7, 8, 9 There has been a renewed interest in the pathogenetic mechanisms involved in the myopathy with recent studies revealing abnormal levels of nitric oxide, elevation of circulating tumor necrosis factor (TNF) receptors, elevated soluble CD40 expression, and increased expression of major histocompatibility complex class I and interleukin 1α within the muscle. The pathogenesis of the cutaneous disease is poorly understood.
The etiology of these disorders is not known. There appear to be immunogenetic markers that are correlated with DM, PM, and additionally, these patients often possess TNF-α polymorphisms.10 What triggers the onset of DM, PM, or juvenile DM has not been established; however, there is some suggestion that the onset of some of the subsets is seasonal,11 and, in children, there is evidence suggesting that the disease might follow an infection.12 It is therefore possible that DM, PM, and/or juvenile DM are due to an interaction of environmental factors including infections in an individual with an immunogenetic predisposition to develop disease.
Section snippets
Classification
Bohan and Peter4 suggested 5 subsets of myositis—DM, PM, myositis with cancer, childhood DM/PM, and myositis overlapping with another collagen vascular disorder. In a subsequent publication, Bohan et al13 noted that cutaneous disease may precede the development of the myopathy; however, it was only recently recognized that another subset of patients with disease that only affects the skin (amyopathic DM [ADM] or DM-sine myositis) may occur.14 A seventh subset known as inclusion body myositis
Diagnosis and evaluation of the patient with DM
The diagnosis of DM is suspected in patients with clinically compatible cutaneous findings. Exclusion of other possible cutaneous conditions is aided by skin biopsy and the recognition of muscle involvement. In the absence of identifiable myopathy, the differentiation from cutaneous LE may be difficult. Muscle weakness may be caused by many other disorders including toxins, infections, metabolic abnormalities, and neurologic disorders.38 The presence of characteristic skin lesions however
Conclusions
Dermatomyositis is a condition primarily of the skin and muscles, but other systemic features may occur. Dermatomyositis is the most common presentation of inflammatory muscle disease in children. Whereas dermatomyositis also occurs in adults, individuals in this age group may also have inflammatory muscle diseases (polymyositis or inclusion body myositis) that do not have cutaneous manifestations. The pathogenesis of the muscle disease is becoming better understood, but the cutaneous disease
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