Since its first description more than a century ago, there has been much debate about the diagnostic entity polymyositis. Because initial observations were of individuals with dermatomyositis, it appeared that polymyositis was not possible without skin lesions. Distinctive clinical and histologic features of polymyositis were not established until the late 20th century. The identification of inclusion body myositis as a distinct entity has further refined nosographic classification.
Bronner IM, Linssen WHJP, van der Meulen MFG, Hoogendijk JE, de Visser M. PolymyositisAn Ongoing Discussion About a Disease Entity. Arch Neurol. 2004;61(1):132-135. doi:10.1001/archneur.61.1.132