Polymyositis: An overdiagnosed entity

To the Editor:

The classification of the inflammatory and immune myopathies is a complex issue. While the Bohan and Peter criteria1 have been used for almost 30 years, recent findings have brought their validity into question. For this reason, we read with interest the study by van der Meulen et al.2 describing a new pathology-driven categorization of these diseases. A biopsy-based approach, however, is not necessarily straightforward. Because the pathology of the inflammatory myopathies is not always homogeneous, such an approach requires extensive study to determine which pathologic criteria are useful and reproducible for the diagnoses of different immune and inflammatory myopathic syndromes.

A shortcoming of the van der Meulen et al. study is the lack of evidence to suggest that their criteria perform any better than the Bohan and Peter criteria in determining diagnosis, treatment, and prognosis. Their new scheme results in polymyositis being condemned to an uncertain status and being replaced with the less-than-helpful categories of “unspecified myositis” and “possible myositis.” The authors’ arguments would be more compelling if they demonstrated that their proposed classifications were more clinically useful than prior ones (i.e., that patients initially classified as polymyositis or dermatomyositis by Bohan and Peter criteria and who did not respond to treatment met their criteria for unspecified myositis). Their proposed classification criteria would leave many myositis patients diagnostically adrift and potentially excluded from receiving effective treatment.

The International Myositis Assessment and Clinical Studies Group (IMACS) is a multidisciplinary coalition of over 100 neurologists, rheumatologists, dermatologists, and other specialists who care for adults and children with inflammatory myopathies. Currently, the IMACS consensus is that probable or definite Bohan and Peter criteria are appropriate for distinguishing polymyositis from dermatomyositis and enrolling adult subjects in trials as long as the muscle biopsy criteria are met. Bohan and Peter …