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OP0035 Progress Report on the Development of New Classification Criteria for Adult and Juvenile Idiopathic Inflammatory Myopathies
  1. A. Tjärnlund1,
  2. M. Bottai2,
  3. L. G. Rider3,
  4. V. P. Werth4,
  5. C. Pilkington5,
  6. M. de Visser6,
  7. L. Alfredsson2,
  8. A. A. Amato7,
  9. R. J. Barohn8,
  10. M. H. Liang9,
  11. J. A. Singh10,
  12. F. W. Miller3,
  13. I. E. Lundberg On behalf of the members of the International Myositis Classification Criteria Project1
  1. 1Rheumatology Unit, Department of Medicine, Karolinska University Hospital, Solna, Karolinska Institutet
  2. 2Institute for Environmental Medicine, Karolinska Institutet, Stockholm, Sweden
  3. 3Environmental Autoimmunity Group, Program of Clinical Research, National Institute of Environmental Health Sciences, National Institutes of Health, US Department of Health and Human Services, Bethesda
  4. 4Department of Dermatology, Philadelphia VAMC and Hospital of the University of Pennsylvania, Philadelphia, United States
  5. 5Department of Rheumatology, Great Ormond Street Hospital for Children NHS Trust, London, United Kingdom
  6. 6Department of Neurology, Academic Medical Centre, Amsterdam, Netherlands
  7. 7Department of Neurology, Brigham and Women’s Hospital, Harvard Medical School, Boston
  8. 8Department of Neurology, University of Kansas Medical Center, Kansas City
  9. 9Division of Rheumatology, Immunology and Allergy, Brigham and Women´s Hospital, Boston
  10. 10University of Alabama and VA Medical Center, Birmingham, United States


Background Inadequate classification criteria for IIM are a fundamental limitation in clinical studies. An international, multidisciplinary collaboration, the International Myositis Classification Criteria Project (IMCCP), supported by ACR and EULAR, was established to address this problem.

Objectives Develop and validate new classification criteria for adult and juvenile IIM and its major subgroups.

Methods Candidate variables were selected from published criteria and inclusion criteria in controlled trials of myositis. Comparator conditions confused with IIM were defined.

Clinical and laboratory data from IIM and comparator patients were collected from 47 rheumatology, dermatology, neurology and pediatrics clinics worldwide from 2008-2011.

Crude pair-wise associations among all measured variables and between each variable and clinicians’ diagnoses were assessed. The explored approaches were:

  1. Traditional: case defined by specified number of items from a set of variables

  2. Probability score: case assigned a probability score by summing score-points associated with a set of variables

  3. Classification tree: case defined by a decision tree

Internal validation using bootstrap methods was performed.

Results Data from 973 IIM patients (74% adults; 26% children), representing subgroups of IIM, and 629 comparators (81% adults; 19% children) were obtained. Two probability score models were developed: Model 1 comprised clinical variables on muscles, skin, and laboratory measures; Model 2 additionally comprised muscle biopsy variables. Model 1 performed nearly as well as Model 2 (specificity 87% vs. 88%, sensitivity 89% vs. 89%, and correctly classified 87% vs. 89%). Both models performed as well as, and often better than, the classification tree that was developed (sensitivity 88%, specificity 72%, and correctly classified 84%) and published criteria.

Conclusions New classification criteria for IIM with readily clinically assessable measurements and symptoms have been developed. They generally show superior performance compared with existing criteria. External validation is in progress.

Disclosure of Interest None Declared

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