RT Journal Article SR Electronic T1 EULAR/ACR classification criteria for adult and juvenile idiopathic inflammatory myopathies and their major subgroups: a methodology report JF RMD Open JO RMD Open FD EULAR SP e000507 DO 10.1136/rmdopen-2017-000507 VO 3 IS 2 A1 Matteo Bottai A1 Anna Tjärnlund A1 Giola Santoni A1 Victoria P Werth A1 Clarissa Pilkington A1 Marianne de Visser A1 Lars Alfredsson A1 Anthony A Amato A1 Richard J Barohn A1 Matthew H Liang A1 Jasvinder A Singh A1 Rohit Aggarwal A1 Snjolaug Arnardottir A1 Hector Chinoy A1 Robert G Cooper A1 Katalin Danko A1 Mazen M Dimachkie A1 Brian M Feldman A1 Ignacio García-De La Torre A1 Patrick Gordon A1 Taichi Hayashi A1 James D Katz A1 Hitoshi Kohsaka A1 Peter A Lachenbruch A1 Bianca A Lang A1 Yuhui Li A1 Chester V Oddis A1 Marzena Olesinka A1 Ann M Reed A1 Lidia Rutkowska-Sak A1 Helga Sanner A1 Albert Selva-O’Callaghan A1 Yeong Wook Song A1 Jiri Vencovsky A1 Steven R Ytterberg A1 Frederick W Miller A1 Lisa G Rider A1 Ingrid E Lundberg A1 , YR 2017 UL http://rmdopen.bmj.com/content/3/2/e000507.abstract AB Objective To describe the methodology used to develop new classification criteria for adult and juvenile idiopathic inflammatory myopathies (IIMs) and their major subgroups.Methods An international, multidisciplinary group of myositis experts produced a set of 93 potentially relevant variables to be tested for inclusion in the criteria. Rheumatology, dermatology, neurology and paediatric clinics worldwide collected data on 976 IIM cases (74% adults, 26% children) and 624 non-IIM comparator cases with mimicking conditions (82% adults, 18% children). The participating clinicians classified each case as IIM or non-IIM. Generally, the classification of any given patient was based on few variables, leaving remaining variables unmeasured. We investigated the strength of the association between all variables and between these and the disease status as determined by the physician. We considered three approaches: (1) a probability-score approach, (2) a sum-of-items approach criteria and (3) a classification-tree approach.Results The approaches yielded several candidate models that were scrutinised with respect to statistical performance and clinical relevance. The probability-score approach showed superior statistical performance and clinical practicability and was therefore preferred over the others. We developed a classification tree for subclassification of patients with IIM. A calculator for electronic devices, such as computers and smartphones, facilitates the use of the European League Against Rheumatism/American College of Rheumatology (EULAR/ACR) classification criteria.Conclusions The new EULAR/ACR classification criteria provide a patient’s probability of having IIM for use in clinical and research settings. The probability is based on a score obtained by summing the weights associated with a set of criteria items.