The review is based on our own experience and research connected with these disorders as well as a comprehensive MEDLINE search on the topics of “polymyositis”, “dermatomyositis”, and “inflammatory myopathies”. We focused on peer-reviewed works published in English in major scientific journals over the past 10 years and on reviews written by experts on this subject. All available articles were critically reviewed. Papers presenting the strongest evidence or providing important insights
SeminarPolymyositis and dermatomyositis
Section snippets
Epidemiology, genetics, and general clinical features
Dermatomyositis affects both children and adults, and women more than men. Polymyositis is seen after the second decade of life. Inclusion-body myositis is more common in men over the age of 50 than in other population groups.1, 2, 3, 4, 5, 6, 7 The frequencies of polymyositis and dermatomyositis as stand-alone disorders or in association with other systemic diseases are unknown. Estimates based on old diagnostic criteria,8 which cannot distinguish polymyositis from inclusion-body myositis,1, 3
Dermatomyositis
Dermatomyositis is identified by a characteristic rash accompanying or, more commonly, preceding muscle weakness. The skin manifestations include a heliotrope rash (blue-purple discolouration) on the upper eyelids in many cases associated with oedema, and an erythematous rash on the face, neck, and anterior chest (in many patients in a V sign) or back and shoulders (shawl sign), knees, elbows, and malleoli; the rash can be exacerbated after exposure to the sun and is pruritic in some cases.
Extramuscular manifestations
There are many manifestations outside the muscles. Joint contractures occur mostly in dermatomyositis. Dysphagia is due to involvement of the oropharyngeal striated muscles and upper oesophagus30, 31 (gastrointestinal ulcerations due to vasculitis and infection were common in children with dermatomyositis before the use of immunosuppressants2). Cardiac disturbances include atrioventricular conduction defects, tachyarrhythmias, myocarditis in patients with acute disease,32, 33 and heart failure
Diagnosis
The clinical diagnosis of polymyositis and dermatomyositis is confirmed by three laboratory examinations: serum muscle enzyme concentrations, electromyography, and muscle biopsy. In certain cases of dermatomyositis, skin biopsy can be helpful.
The most sensitive muscle enzyme assay is creatine kinase, which is increased up to 50 times in active disease. Aspartate and alanine aminotransferases, lactate dehydrogenase, and aldolase are also increased. Although creatine kinase concentration usually
Diagnostic criteria
The subject of diagnostic criteria remains unsettled because the various proposed criteria3 have not been properly validated. The criteria of Bohan and Peter8 cannot distinguish polymyositis from inclusion-body myositis or from certain dystrophies. Because the immunopathological characteristics confer specificity for each subset, we believe that the diagnostic criteria should rely on histopathology and immunopathology as the best means of separating polymyositis from other myopathies.1
Immunopathogenesis
The autoimmune origin of polymyositis and dermatomyositis is supported by their association with other autoimmune disorders, autoantibodies,60 and histocompatibility genes; the evidence of T-cell-mediated myocytotoxicity or complement-mediated microangiopathy; the possible maternal microchimerism in juvenile forms;61 and their response to immunotherapies. However, no specific target antigens have been identified, and the agents initiating self-sensitisation remain unknown.
Treatment
The goals of therapy are to improve the ability to carry out activities of daily living by increasing muscle strength and to ameliorate extramuscular manifestations (rash, dysphagia, dyspnoea, arthralgia, fever). There have been very few controlled clinical trials, most on dermatomyositis and inclusion-body myositis.135 Overall, dermatomyositis responds better than polymyositis, and inclusion-body myositis is difficult to treat. Although when the strength improves, the serum creatine kinase
Prognosis
Although the disease outcome has substantially improved, at least a third of patients are left with mild to severe disability.154, 155, 156 Older age and association with cancer are factors associated with poor prognosis. Pulmonary fibrosis, frequent aspiration pneumonias due to oesophageal dysfunction, and calcinosis in dermatomyositis are associated with increased morbidity.154, 155, 156 In a small cohort, the 5-year survival was 95% and the 10-year survival 84%.156
Conclusion
On the basis of our own experience and that of others in major neuromuscular centres, the diagnosis and treatment of dermatomyositis and polymyositis could be improved by modification of many common practices. First, all disorders that mimic polymyositis should be excluded, taking into account that the criteria of Bohan and Peter cannot separate polymyositis from inclusion-body myositis or other toxic, necrotising, and dystrophic myopathies. Second, polymyositis as a stand-alone entity is rare.
Search strategy and selection criteria
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The heart and cardiac conduction system in polymyositis-dermatomyositis: a clinicopathologic study of 16 autopsied patients
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The immunobiology of muscle
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Interstitial lung disease with autoantibodies against aminoacyl-tRNA synthetases in the absence of clinically apparent myositis
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Differences in idiopathic inflammatory myopathy phenotypes and genotypes between Mesoamerican Mestizos and North American Caucasians
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Is there dermatomyositis (DM) without myositis?
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Scleroderma-polymyositis overlap syndrome: clinical and serologic aspects
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Association of the eosinophilia-myalgia syndrome with the ingestion of tryptophan
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Fatal polymyositis in D-penicillamine-treated rheumatoid arthritis
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Mitochondrial myopathy caused by long-term zidovudine therapy
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Adverse effects of drugs on muscle
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Diseases of muscle and the neuromuscular junction
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Cricopharyngeal muscle dysfunction in the differential diagnosis of dysphagia in polymyositis
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Esophageal abnormalities and dysphagia in polymyositis and dermatomyositis: clinical, radiographic and pathologic features
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Severe cardiac involvement in children with systemic sclerosis and myositis
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