Katalin Dankó

OBJECTIVE: To develop and validate new classification criteria for adult and juvenile idiopathic inflammatory myopathies (IIM) and their major subgroups. METHODS: Candidate variables were assembled from published criteria and expert opinion using consensus methodology. Data were collected from 47 rheumatology, dermatology, neurology, and pediatric clinics worldwide. Several statistical methods were utilized to derive the classification criteria. RESULTS: Based on data from 976 IIM patients (74% adults; 26% children) and 624 non-IIM patients with mimicking conditions (82% adults; 18% children), new criteria were derived. Each item is assigned a weighted score. The total score corresponds to a probability of having IIM. Subclassification is performed using a classification tree. A probability cutoff of 55%, corresponding to a score of 5.5 (6.7 with muscle biopsy) "probable IIM," had best sensitivity/specificity (87%/82% without biopsies, 93%/88% with biopsies) and is recommended as a minimum to classify a patient as having IIM. A probability of ≥90%, corresponding to a score of ≥7.5 (≥8.7 with muscle biopsy), corresponds to "definite IIM." A probability of <50%, corresponding to a score of <5.3 (<6.5 with muscle biopsy), rules out IIM, leaving a probability of ≥50-<55% as "possible IIM." CONCLUSION: The European League Against Rheumatism/American College of Rheumatology (EULAR/ACR) classification criteria for IIM have been endorsed by international rheumatology, dermatology, neurology, and pediatric groups. They employ easily accessible and operationally defined elements, and have been partially validated. They allow classification of "definite," "probable," and "possible" IIM, in addition to the major subgroups of IIM, including juvenile IIM. They generally perform better than existing criteria.

The idiopathic inflammatory myopathies are characterized by chronic muscle inflammation and involvement of internal organs, which contribute considerably to the morbidity and mortality of the disease. We conducted the current study to determine the survival data for patients with idiopathic inflammatory myopathies according to the presence of extramuscular clinical manifestations. We also determined the cumulative survival probability and the long-term prognosis and analyzed the causes of death at a single clinical immunology center.A survival analysis was performed using data for 162 patients diagnosed between 1976 and 1997 according to Bohan and Peter's criteria. Patients were followed up for a minimum of 5 years (median, 101.5 mo) or to date of death. Cumulative survival probability was calculated by the Kaplan-Meier method. The influence of extraskeletal and extramuscular involvement was analyzed as prognostic factors for death by Cox proportional hazards survival model. Eighteen disease-specific deaths occurred; pulmonary and cardiac complications were the most frequent causes of death. Global survival rates were 95%, 92%, and 89% for 1, 5, and 10 years, respectively. Analysis for clinicopathologic subgroups revealed that cancer-associated myositis had the worst prognosis, while juvenile and overlap myositis had the best prognosis. Five- and 10-year survival rates were 94.2% and 89.4% for patients with primary polymyositis and 90.1% and 86.4% for primary dermatomyositis patients, respectively. In the whole group of patients with idiopathic inflammatory myopathy, cardiac (p < 0.01) and respiratory muscle involvement (p = 0.045) were significant prognostic factors for death. In the group of patients with primary polymyositis/dermatomyositis, cardiac involvement was the main prognostic factor for death (p < 0.01). Myositis patients described in this study have higher survival rates than reported previously worldwide. We examine the reasons for the differences between the data in the current study and the available survival data in the relevant literature.

OBJECTIVES: To determine prevalence and co-existence of myositis specific autoantibodies (MSAs) and myositis associated autoantibodies (MAAs) and associated clinical characteristics in a large cohort of idiopathic inflammatory myopathy (IIM) patients. METHODS: Adult patients with confirmed IIM recruited to the EuroMyositis registry (n = 1637) from four centres were investigated for the presence of MSAs/MAAs by radiolabelled-immunoprecipitation, with confirmation of anti-MDA5 and anti-NXP2 by ELISA. Clinical associations for each autoantibody were calculated for 1483 patients with a single or no known autoantibody by global linear regression modelling. RESULTS: MSAs/MAAs were found in 61.5% of patients, with 84.7% of autoantibody positive patients having a sole specificity, and only three cases (0.2%) having more than one MSA. The most frequently detected autoantibody was anti-Jo-1 (18.7%), with a further 21 specificities each found in 0.2-7.9% of patients. Autoantibodies to Mi-2, SAE, TIF1, NXP2, MDA5, PMScl and the non-Jo-1 tRNA-synthetases were strongly associated (p < 0.001) with cutaneous involvement. Anti-TIF1 and anti-Mi-2 positive patients had an increased risk of malignancy (OR 4.67 and 2.50 respectively), and anti-SRP patients had a greater likelihood of cardiac involvement (OR 4.15). Interstitial lung disease was strongly associated with the anti-tRNA synthetases, anti-MDA5, and anti-U1RNP/Sm. Overlap disease was strongly associated with anti-PMScl, anti-Ku, anti-U1RNP/Sm and anti-Ro60. Absence of MSA/MAA was negatively associated with extra-muscular manifestations. CONCLUSIONS: Myositis autoantibodies are present in the majority of patients with IIM and identify distinct clinical subsets. Furthermore, MSAs are nearly always mutually exclusive endorsing their credentials as valuable disease biomarkers.