VIENNA -- A new set of criteria to classify idiopathic inflammatory myopathies was more specific and sensitive than current diagnostic methods, researchers reported here.
The new criteria were able to correctly classify 87% of idiopathic inflammatory myopathies without muscle biopsy data with a sensitivity of 87% and a specificity of 88%, and correctly classify 88% of cases with muscle biopsy data with a sensitivity of 88% and a specificity of 89%, according to Marianne de Visser, MD, of the Academic Medical Center in Amsterdam, the Netherlands, and colleagues.
However, the criteria had worse prognostic probability when used to diagnose inclusion body myositis without muscle biopsy data (78%) and when used to diagnose polymyositis with (74%) or without (73%) muscle biopsy data, de Visser said at an oral presentation during the World Congress of Neurology.
Session moderator Eva Feldman, MD, PhD, of the University of Michigan Health System in Ann Arbor, noted that the inclusion of body myositis accuracy was particularly cautionary, as "you would not want to misclassify and inappropriately treat it."
She added that through their plan to analyze data from an additional 1,000 patients, the researchers may be able to refine and increase the accuracy of the diagnostic system. However, she said she "was extremely impressed with the monumental task they've undertaken and how well they've done it."
"There is no consensus on the classification of idiopathic inflammatory myopathies," de Visser noted, adding that current identifying criteria are often not specific and do not distinguish polymyositis from inclusion body myositis or mimics.
The researchers developed criteria for clinical and basic research that distinguished idiopathic inflammatory myopathies from other mimicking conditions with high sensitivity and specificity, and that could distinguish major subgroups of the condition from each other accurately.
Data were collected from 973 patients with an idiopathic inflammatory myopathy, and from 629 patients with mimicking conditions, as part of the International Myositis Classification Criteria Project. These data were used to assess 75 clinical and laboratory variables to determine a patient's probability, or risk score.
Participants were included if they had received a diagnosis for at least 6 months and if the physician was certain of the diagnosis. Data recorded on patients included gender, age, ethnicity, pattern of muscle weakness, skin manifestations, response to treatment dysphagia, electromyogram, MRI, laboratory data on muscle enzymes and autoantibodies, and information gathered from muscle biopsy on histopathology, immunohistochemistry, and electron microscopy.
Comparator cases included dystrophies, drug- and toxin-associated myopathies, metabolic myopathies, mitochondrial myopathies, endocrine myopathies, rheumatic conditions, and dermatologic conditions.
Risk scores utilized skin variables, clinical muscle variables, age of onset of first symptoms, other clinical variables, laboratory variables, and variables from muscle biopsy. Scores were out of a possible 12 points.
De Visser noted that the research is still ongoing and that she and her co-authors would like to improve accuracy of the criteria in diagnosing polymyositis and inclusion body myopathy. She added that additional validation was incoming from other cohorts and that consensus on new classification criteria was needed.
The study was supported by the Myositis Association.
The authors declared no conflicts of interest.
- Reviewed by Robert Jasmer, MD Associate Clinical Professor of Medicine, University of California, San Francisco and Dorothy Caputo, MA, BSN, RN, Nurse Planner
World Congress of NeurologySource Reference: de Visser M, et al "Progress report on the development of new classification criteria for adult and juvenile idiopathic inflammatory myopathies" WCN 2013.