Overlap myositis, a distinct entity beyond primary inflammatory myositis: A retrospective analysis of a large cohort from the REMICAM registry.

BACKGROUND: Inflammatory idiopathic myositis (IIM) comprises a heterogeneous group of systemic muscular diseases that can occur together with other connective tissue diseases (CTD), named overlap myositis (OM). The question of whether OM is a distinct entity still remains controversial. AIM: The present study was conducted to assess the clinical and prognostic differences between patients diagnosed with OM, primary polymyositis (PM) and primary dermatomyositis (DM). METHOD: The study consists of a retrospective longitudinal and multicenter series of IIM patients. Patients were classified as OM, PM and DM. Overlap myositis was defined as patients fulfilling criteria for IIM plus criteria for other CTD (namely systemic sclerosis, systemic lupus erythematosus, mixed connective tissue disease, rheumatoid arthritis and primary Sjögren's syndrome). RESULT: A total of 342 patients were included (98 OM, 137 PM and 107 DM). Overlap myositis patients, in comparison with PM and DM, showed significant differences, with more extramuscular involvement, particularly more arthritis (66%, 34.6% and 48.1%, respectively), puffy fingers (49.5%, 11.1% and 24.3%), sclerodactyly (45.4%, 2.2% and 2%), dysphagia (41.8%, 18.2% and 26.4%), Raynaud phenomenon (65.3%, 16.9% and 19.8%), leucopenia (28.9%, 2.2% and 8.4%), thrombocytopenia (8.2%, 2.2% and 1.9%), interstitial lung disease (ILD) (48%, 35% and 30.8%), renal manifestations (13.4%, 3.7% and 1.9%), and more severe infections (41.3%, 26.7% and 21%). No significant differences were found in survival between groups in log rank test (P = 0.106). Multivariate adjusted survival analyses revealed a worse prognosis for severe infections, ILD and baseline elevation of acute phase reactants. CONCLUSION: Overlap myositis stands out as a distinct entity as compared to PM and DM, featuring more extramuscular involvement and more severe infections. Close monitoring is recommended in this subset for early detection and treatment of possible complications.

Mortality and prognostic factors in idiopathic inflammatory myositis: a retrospective analysis of a large multicenter cohort of Spain.

The present study was undertaken to assess mortality, causes of death, and associated prognostic factors in a large cohort of patients diagnosed with idiopathic inflammatory myositis (IIM) from Spain. A retrospective longitudinal study was carried out in 467 consecutive patients with IIM, identified from 12 medical centers. Patients were classified as primary polymyositis, primary dermatomyositis (DM), overlap myositis, cancer-associated myositis (CAM), and juvenile idiopathic inflammatory myopathies. A total of 113 deaths occurred (24%) after a median follow-up time of 9.7 years. In the overall cohort, the 2-, 5-, and 10-year survival probabilities were 91.9, 86.7, and 77%, respectively. Main causes of death were infections and cancer (24% each). Multivariate model revealed that CAM (HR = 24.06), OM (HR = 12.00), DM (HR = 7.26), higher age at diagnosis (HR = 1.02), severe infections (HR = 3.66), interstitial lung disease (HR = 1.61), and baseline elevation of acute phase reactants (HR = 3.03) were associated with a worse prognosis, while edema of the hands (HR = 0.39), female gender (HR = 0.39), and longer disease duration (HR = 0.73) were associated with a better prognosis. The standardized mortality ratio was 1.56 (95% CI 1.28-1.87) compared to the Spanish general population. Our findings indicate that IIM has a high long-term mortality, with an excess of mortality compared to the Spanish population. A more aggressive therapy may be required in IIM patients presenting with poor predictive factors.