Polymyositis And Dermatomyositis

Polymyositis (PM) and dermatomyositis (DM) are idiopathic inflammatory myopathies of autoimmune origin involving the skeletal muscles. Pulmonary involvement occurs and is a source of morbidity and mortality. The main forms of pulmonary involvement include interstitial lung disease, respiratory muscle weakness, and aspiration pneumonia. Non-specific interstitial pneumonia, organizing pneumonia, usual interstitial pneumonia, diffuse alveolar damage, and lymphocytic interstitial pneumonia are the main histologic patterns found. Anti-Jo-1 antibody (anti-histidyl-tRNA synthetase) is commonly found in patients with PM/DM-associated interstitial lung disease. Progressive interstitial lung disease and respiratory muscle weakness can both cause respiratory failure. Aspiration pneumonia is related to weakness of the pharyngeal and upper esophageal muscles. Uncommon pulmonary manifestations include pleural effusion and pleuritis, pulmonary hypertension, and vasculitis. Corticosteroid therapy is the first line treatment and is generally effective in controlling both the myositis and the pulmonary involvement. However, in some patients PM/DM deteriorates despite corticosteroids and immunosuppressive therapy. Better understanding of the pathogenetic mechanisms in PM/DM will lead to more specific, target-directed therapy.