polymyositis
noun
poly·myo·si·tis ˌpä-lē-ˌmī-ə-ˈsī-təs 
: inflammation of several muscles at once
specifically : an inflammatory muscle disease of unknown cause that affects muscles and chiefly skeletal muscles and is characterized especially by weakness of the muscles (such as those of the shoulder, neck, or hip) closest to the trunk see dermatomyositis
Example Sentences
Recent Examples on the Web Like polymyositis, it is characterized by weakness of the shoulders and thighs and retained strength in the hands and feet. 
New York Times, 26 May 2022 Another possibility was polymyositis, an autoimmune disorder in which the patient’s immune system attacks the muscles. New York Times, 26 May 2022 One of them is a gene for toll-like receptor 7, or TLR-7, a protein that has been implicated in autoimmune disorders such as lupus, polymyositis, scleroderma and Sjogren’s syndrome. Melinda Wenner Moyer, Scientific American, 1 Sep. 2021 Estrada was diagnosed at the age of 14 with polymyositis, a disease that wastes away muscles and has no cure. Washington Post, 30 Dec. 2019
New York Times, 26 May 2022 Another possibility was polymyositis, an autoimmune disorder in which the patient’s immune system attacks the muscles. New York Times, 26 May 2022 One of them is a gene for toll-like receptor 7, or TLR-7, a protein that has been implicated in autoimmune disorders such as lupus, polymyositis, scleroderma and Sjogren’s syndrome. Melinda Wenner Moyer, Scientific American, 1 Sep. 2021 Estrada was diagnosed at the age of 14 with polymyositis, a disease that wastes away muscles and has no cure. Washington Post, 30 Dec. 2019 Word History
First Known Use
1877, in the meaning defined above
Medical Definition
polymyositis
noun
poly·myo·si·tis -ˌmī-ə-ˈsīt-əs
: inflammation of several muscles at once
specifically : an inflammatory disease of unknown cause that affects muscles and especially skeletal muscles, is characterized typically by weakness usually of the proximal muscles (such as those of the shoulder or pelvic girdles or of the neck), muscle and joint pain, pathological muscle changes (such as fiber degeneration or infiltration by lymphocytes), pneumonia, and cardiac abnormalities (such as arrhythmia or myocarditis)
Dermatomyositis affects both children and adults, and females more often than males, whereas polymyositis is seen after the second decade of life and very rarely in childhood. Marinos C. Dalakas, The New England Journal of Medicine
see dermatomyositis Marinos C. Dalakas, The New England Journal of Medicine