Polymyositis (PM) is an idiopathic inflammatory myopathy with systemic manifestations and mediated by autoimmune and cellular mechanisms. It results in proximal muscle weakness and often chronic disability. Systemic complications, in particular, lung involvement, are responsible for increased morbidity and mortality. In the United States 5 to 10 new cases of PM or its related disorder dermatomyositis (DM) per million population is discovered yearly.<sup>58 Plotz P.H., Dalakas M., Leff R.L. , e al. Current concepts in the idiopathic inflammatory myopathies: Polymyositis, dermatomyositis, and related disorders Ann Intern Med 1989 ;  111 : 143-157

Cliccare qui per andare alla sezione Riferimenti</sup> Women are more apt to be affected than men, and there is a predilection for African-American women.<sup>52 Oddis C.V., Medsger T. Current management of polymyositis and dermatomyositis Drugs 1989 ;  37 : 382-390  [cross-ref]

Cliccare qui per andare alla sezione Riferimenti</sup> There are two disease peaks: one in children and the other in young to middle-aged adults.<sup>28 Hoffman G.S., Franck W.A., Raddatz D.A. , e al. Presentation, treatment, and prognosis of inflammatory muscle disease in a rural hospital Am J Med 1983 ;  75 : 433-438  [cross-ref]

Cliccare qui per andare alla sezione Riferimenti</sup> A classification of PM follows<sup>54 Pearson C.M. Polymyositis and dermatomyositis Arthritis and Allied Conditions Philadelphia: Lea and Febiger (1972).  940-961

Cliccare qui per andare alla sezione Riferimenti</sup>:

Polymyositis and DM are similar except for the prominent dermatologic rash and less muscle involvement in DM. The onset of PM or DM in an elderly patient may be the result of an underlying malignancy. Although sometimes disputed, Manchel et al, using strict criteria, found malignancy in 15 of 71 patients with PM or DM.<sup>45 Manchul L.A., Jin A., Pritchard K.I. , e al. The frequency of malignant neoplasms in patients with polymyositis-dermatomyositis: A controlled study Arch Intern Med 1985 ;  145 : 1835-1839

Cliccare qui per andare alla sezione Riferimenti</sup> These subjects were over 50 years with primaries in either the colon, breast, prostate, lung, or uterus. The neoplasm either predated, appeared concomitantly with, or became apparent at some point following the diagnosis of PM or DM. Neoplasms that preceded the onset were present for up to 20 years before the episode of PM or DM. In malignancies that appeared after the diagnosis of PM or DM, there was a 1- to 4-year delay. Two other studies indicated that DM but not PM is associated with an increased incidence of malignancy.<sup>1 Airio A., Pukkala E., Isomaki H. Elevated cancer incidence in patients with dermatomyositis: A population based study J Rheumatol 1995 ;  22 : 1300-1303

Cliccare qui per andare alla sezione Riferimenti, 88 Zantos D., Zhang Y., Felson D. The overall and temporal association of cancer with polymyositis and dermatomyositis J Rheumatol 1994 ;  21 : 1855-1859

Cliccare qui per andare alla sezione Riferimenti</sup>

Polymyositis can also complicate the course of another collagen vascular disease and myositis can be a prominent manifestation of systemic lupus erythematosus, scleroderma, mixed connective tissue disease, and less frequently rheumatoid arthritis. This form of the inflammatory myopathy invariably occurs in women.<sup>52 Oddis C.V., Medsger T. Current management of polymyositis and dermatomyositis Drugs 1989 ;  37 : 382-390  [cross-ref]

Cliccare qui per andare alla sezione Riferimenti</sup>