Dermatomyositis (DM) and polymyositis (PM) are classified as idiopathic inflammatory myopathies. Defining the optimal treatment regimens for these disorders has been difficult because of the rarity of these disorders, their highly complex clinical phenotypes, and the limited number of randomized, double-blind clinical trials [1-3].
In addition, understanding of the inflammatory myopathies has evolved over the years, but disease classification schemes have not kept pace. Newer classifications, based upon histologic and serologic distinctions between the different disorders, may help define the natural history of these diseases better, may assist in the design of well-conceived randomized clinical trials, and may lead to the development of rational therapies [4-6].
The initial therapy of DM and PM will be reviewed here. The treatment of recurrent or resistant disease, the clinical manifestations and approach to diagnosis of these disorders in adults, the management of cutaneous manifestations of dermatomyositis, and issues related to DM and PM in children are discussed separately. (See "Treatment of recurrent and resistant dermatomyositis and polymyositis in adults" and "Clinical manifestations and diagnosis of adult dermatomyositis and polymyositis" and "Initial management of cutaneous dermatomyositis" and "Management of refractory cutaneous dermatomyositis" and "Pathogenesis and clinical manifestations of juvenile dermatomyositis and polymyositis" and "Treatment and prognosis of juvenile dermatomyositis and polymyositis".)
PREDICTORS OF OUTCOME
The severity of disease in DM and PM is highly variable, ranging from mild weakness that responds readily to treatment to muscle dysfunction associated with a relentless downhill course that is unresponsive to all treatment modalities. Some clinical and laboratory features are associated with a poorer prognosis.
Clinical predictors — Most studies that have investigated prognosis in the inflammatory myopathies did not distinguish between DM and PM. Many also did not recognize inclusion body myositis, a common mimic of PM that is associated with a worse prognosis but was not defined until the 1980s. (See "Clinical manifestations and diagnosis of inclusion body myositis".)