Historical note and terminology
Although first recorded by Wagner in 1863 (140), polymyositis became a recognized clinical entity 75 years later when Walton and Adams published a remarkable monograph titled Polymyositis (141). These authors defined the term “polymyositis” as an all-inclusive designation of a group of myopathies characterized by a single basic disease process related to "other collagen" diseases or arising as the result of "hypersensitivity response to allergic inflammation." Today, described by neurologists as a neuromuscular disorder, polymyositis is cared for not only by neurologists but also by rheumatologists, who approach the illness as in a setting of other rheumatic diseases. Polymyositis is a rare disorder that, by all accounts, is the most overdiagnosed acquired myopathy. It is discussed in conjunction with 3 similar but more distinct and more frequent entities as evolved in the last decade, namely necrotizing myositis, myofasciitis, and overlap myositis.
The study of polymyositis requires a scholarly review of the neurologic examination, muscle histopathology, immunopathology, and biochemistry to ensure that toxic, metabolic, or mitochondrial muscle diseases are not missed and that 2 more common entities, the inclusion body myositis and the necrotizing autoimmune myositis, are not overlooked (12; 67; 29; 30; 36; 37; 39; 46; 47; 49; 122; 40; 106; 46; 46).