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ACR, EULAR Release Classification Criteria for Idiopathic Inflammatory Myopathies
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The American College of Rheumatology and The European League Against Rheumatism have released their 2017 classification criteria for juvenile and adult idiopathic inflammatory myopathies and their major subgroups, which were published in Arthritis and Rheumatology.
The criteria allow for idiopathic inflammatory myopathies (IIM) to be classified as “definite,” “probable,” and possible.” They also allow classification of IIM subgroups, including dermatomyositis (DM), polymyositis (PM) and inclusion body myositis (IBM), as well as juvenile DM (JDM).
“The currently available classification criteria for IIM have several limitations, such as they have not been data driven, and they capture patients with some but not all phenotypes of myositis,” Ingrid E. Lundberg, MD, of Karolinska University Hospital, in Stockholm, told Healio Rheumatology.
According to Lundberg, the new criteria are data-driven, based on data from patients and comparators from 47 rheumatology, dermatology, neurology and pediatric clinics worldwide.
“Each variable is given a different score, and the sum of the scores gives a probability of having IIM,” Lundberg said. “The new EULAR/ACR classification criteria for adult and juvenile IIM, and their major subgroups, capture patients with typical skin rash of dermatomyositis without clinically manifest muscle weakness so-called clinically amyopathic dermatomyositis or hypomyopathic dermatomyositis.”
In addition, the new criteria have a good feasibility, high sensitivity and specificity, have been partly validated in external cohorts, and are superior to previous criteria in capturing different subgroups of IIM, according to the authors.
The International Myositis Classification Criteria Project formed in 2004 as an international collaboration of experts in adult and pediatric rheumatology, neurology, dermatology, epidemiology and biostatistics. Their specific goal was to identify clinical and laboratory features that distinguish IIM from mimicking conditions, with high sensitivity and specificity, and to distinguish IIM’s major subgroups.
The researchers assembled candidate variables from published criteria and expert opinion using consensus methodology. Data were collected from 47 centers in Europe, North America, South America and Asia. In addition, several statistical methods were used to derive the classification criteria, the researchers said.
The researchers analyzed data from 976 patients with IIM, 74% of whom were adults, and 624 patients without IIM, of whom 82% were adults.
Based on their data and research, the classification team developed the following recommendations:
Patients with pathognomonic skin rashes — such as heliotrope rash, Gottron's papules, and Gottron's sign — of JDM or DM are accurately grouped with the EULAR/ACR classification criteria without including muscle biopsy data. For patients without these skin manifestations, muscle biopsy is recommended, and for patients with DM without muscle involvement, a skin biopsy is recommended;
The new classification criteria provide a score and probability of IIM. According to the researchers, each probability displays a unique sensitivity and specificity. For example, the best balance between sensitivity and specificity can be found for a probability of 55% to 60%, which represents a total aggregated score of 5.5 to 5.7, for the criteria not including muscle biopsy data, and 55% to 75%, representing a total aggregated score of 6.7 to 7.6, when including muscle biopsies. These cases are designated “probable IIM.” The recommended cutoff needed for classifying a patient as having IIM is at least 55%;
A probability of at least 90%, or a total aggregate score of 7.5 or more without muscle biopsy, and 8.7 with muscle biopsy, is classified as “definite IIM.” This classification is recommended in studies where a high specificity is required;
If the probability is at 50% or greater but less than 55% — a minimum score of 5.3 without biopsies and 6.5 with biopsies — then the patient is termed “possible IIM”; and
For clarity and transparency, both the descriptive term — “possible,” “probable,” or “definite” — as well as the probability and the aggregated score, should be reported in studies.
According to the authors, the new criteria including muscle biopsy features reported high sensitivity of 93%, and a specificity of 88%. The researchers added that there was slightly lower performance without biopsy variables, with a sensitivity of 87% and a specificity of 82%.
The criteria will need revisions in the future when additional validated myositis autoantibody tests, imaging, and other tests are available in more IIM cases and comparator cases without IIM, they added.
“These are classification criteria, to be used in research and are based on cases with at least 6 months observation after diagnosis,” Lundberg said. “A web calculator has also been developed to facilitate classification of IIM or non-IIM, which is available at www.imm.ki.se/biostatistics/calculators/iim.” – by Jason Laday
Disclosure: The researchers report funding from the European League Against Rheumatism, the American College of Rheumatology, The Myositis Association and in part by the NIH, the European Science Foundation for the Euromyositis Register, the Swedish Research Council and the regional agreement on medical training and clinical research between the Stockholm County Council and the Karolinska Institutet. See the full study to additional author disclosures.
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