Current Concepts in the Idiopathic Inflammatory Myopathies: Polymyositis, Dermatomyositis, and Related Disorders

Abstract

Idiopathic inflammatory myopathy, a category encompassing polymyositis, dermatomyositis, and a number of other disorders, is very uncommon, but has been the focus of intense study in the Arthritis and Rheumatism Branch of the National Institute of Arthritis and Musculoskeletal and Skin Diseases for the past several years. We describe the clinical picture, stressing the need for biopsy to ensure correct diagnosis. It is especially important to recognize the treatment-resistant variant, inclusion body myositis. The extraskeletal manifestations, particularly the cardiopulmonary, oropharyngeal, gastrointestinal, and endocrine involvement, are described. The cardiopulmonary involvement, especially interstitial lung disease, arrhythmias, and cardiac failure, may dominate the clinical picture. The known causes are varied, and include drugs, toxins, and some infectious agents, however, in most cases a cause cannot yet be identified. Circumstantial evidence suggests that picornaviruses may initiate some cases in humans, and a very similar disease in mice caused by a picornavirus is actively under study. Studies of autoantibodies and cellular immune function support a central role for disordered immunity in the pathogenesis. The myositis-specific autoantibodies, especially those directed at certain enzymes important in protein synthesis (the aminoacyl-transfer RNA synthetases), are found in a clinically distinct subset of patients. Although most patients respond initially to corticosteroids, cytotoxic drugs are sometimes added when steroid toxicity or refractoriness develops. We describe several newer therapies under study for such cases and outline future directions in research.

Myopathy with mitochondrial alterations in patients with primary biliary cirrhosis and antimitochondrial antibodies

“…Patient 1 displayed certain clinical and pathologic features of systemic sclerosis (Raynaud's phenomenon, esophageal hypomotility, interstitial lung disease, and contraction band necrosis of the heart), but had no clinical or histologic evidence of cutaneous involvement. The clinical evolution of muscle weakness and the pattern of visceral organ involvement and EMG abnormalities in these 2 patients were suggestive of an inflammatory myopathy (16,17). Both patients had HLA-DRw52, a haplotype seen with increased frequency among white patients with idiopathic inflammatory myopathies (17).…”

Anaerobic exercise capacity in patients with juvenile‐onset idiopathic inflammatory myopathies

“…The decrease in anaerobic exercise capacity might also be explained by the fact that during high-intensity exercise, such as in WAnT, type II muscle fibers are recruited predominantly. Corticosteroid therapy causes a more pronounced atrophy of these type II muscle fibers compared with type I muscle fibers (22), which might account for the decreased anaerobic exercise capacity. The limited cycle exercise may be influenced by leg muscle weakness.…”

Diagnosis of dermatomyositis and polymyositis: a study of 102 cases

“…The skin manifestations include a heliotrope rash (blue-purple discoloration) on the upper eyelids with edema, a flat red rash on the face and upper trunk, and erythema of the knuckles accompanied by a raised, violaceous scaly eruption (Gottron's sign). The incidence of PM, DM and inclusion-body myositis is approximately 1 in 100,000 3,5 . The cause of those diseases is still ignored, but the existence of genetic factors and autoimmune mechanisms is known 1,2,4,6 .…”