Polymyositis is an autoimmune condition (thought to be T-cell mediated) resulting in muscle inflammation and destruction that can occur as an isolated syndrome or as a part of any of several systemic autoimmune diseases such as Crohn disease, systemic lupus, celiac disease, Sjogren syndrome, Behcet's, sarcoidosis, and many others. Polymyositis can be differentiated from dermatomyositis by findings on muscle biopsy and the absence of dermatological findings.