Most studies reporting the incidence of idiopathic inflammatory myopathies (IIM) combine dermatomyositis (DM) and polymyositis (PM) and do not include patients with clinically amyopathic DM. In the US, the annual incidence of adult IIM is 5.5 to 8.9 cases per million.[5]Medsger TA, Dawson WN Jr, Masi AT. The epidemiology of polymyositis. Am J Med. 1970;48:715-723.
http://www.ncbi.nlm.nih.gov/pubmed/5420557?tool=bestpractice.com
[6]Kurland LT, Hauser WA, Ferguson RH, et al. Epidemiologic features of diffuse connective tissue disorders in Rochester, Minn., 1951 through 1967, with special reference to systemic lupus erythematosus. Mayo Clin Proc. 1969;44:649-663.
http://www.ncbi.nlm.nih.gov/pubmed/4390370?tool=bestpractice.com
[7]Oddis CV, Conte CG, Steen VD, et al. Incidence of polymyositis-dermatomyositis: a 20-year study of hospital diagnosed cases in Allegheny County, PA 1963-1982. J Rheumatol. 1990;17:1329-1334.
http://www.ncbi.nlm.nih.gov/pubmed/2254890?tool=bestpractice.com
There is a trend towards increasing incidence over time, but this is likely to reflect improved diagnosis and reporting rather than a true increase in disease incidence.[5]Medsger TA, Dawson WN Jr, Masi AT. The epidemiology of polymyositis. Am J Med. 1970;48:715-723.
http://www.ncbi.nlm.nih.gov/pubmed/5420557?tool=bestpractice.com
[6]Kurland LT, Hauser WA, Ferguson RH, et al. Epidemiologic features of diffuse connective tissue disorders in Rochester, Minn., 1951 through 1967, with special reference to systemic lupus erythematosus. Mayo Clin Proc. 1969;44:649-663.
http://www.ncbi.nlm.nih.gov/pubmed/4390370?tool=bestpractice.com
[7]Oddis CV, Conte CG, Steen VD, et al. Incidence of polymyositis-dermatomyositis: a 20-year study of hospital diagnosed cases in Allegheny County, PA 1963-1982. J Rheumatol. 1990;17:1329-1334.
http://www.ncbi.nlm.nih.gov/pubmed/2254890?tool=bestpractice.com
In Spain, the annual incidence of dermatomyositis has been determined at 4.9 per million.[8]Vargas-Leguas H, Selva-O'Callaghan A, Campins-Marti M, et al. Polymyositis-dermatomyositis: incidence in Spain (1997-2004). Medicina Clinica. 2007;129:721-724. [In Spanish]
http://www.ncbi.nlm.nih.gov/pubmed/18053482?tool=bestpractice.com
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