Predictors of myositis in mixed connective tissue disease: a multicentre retrospective study
Authors:   Rheumatology Unit, Centro Hospitalar Universitário Lisboa Central,  Lisbon, Portugal, Melo AT , Silvério-António M ,   Rheumatology Department, Centro Hospitalar  Universitário Lisboa Norte, Centro Académico de Medicina de  Lisboa, Lisbon, Portugal; 3Rheumatology Research Unit, Instituto  de Medicina Molecular, Faculdade de Medicina, Universidade de  Lisboa, Centro Académico de Medicina de Lisboa, Lisbon, Portugal, Martins-Martinho J ,   Rheumatology Department, Centro Hospitalar  Universitário Lisboa Norte, Centro Académico de Medicina de  Lisboa, Lisbon, Portugal; 3Rheumatology Research Unit, Instituto  de Medicina Molecular, Faculdade de Medicina, Universidade de  Lisboa, Centro Académico de Medicina de Lisboa, Lisbon, Portugal, Guimarães F ,   Rheumatology Department, Unidade Local de Saúde do Alto  Minho, Ponte de Lima, Portugal, Dourado E ,   Rheumatology Department, Centro Hospitalar do Baixo Vouga, Aveiro, Portugal; Aveiro  Rheumatology Research Center, Egas Moniz Health Alliance,  Aveiro, Portuga, Oliveira D ,   Rheumatology Department, Centro Hospitalar Universitário São João, Porto, Portugal; Center for Health Technology and Services Research (CINTESIS), Faculty of Medicine,  University of Porto, Porto, Portugal, Lopes J ,   Rheumatology Department,  Hospital Garcia de Orta, Lisboa, Portugal, Saraiva A ,   Rheumatology  Department, Centro Hospitalar Universitário de Coimbra, Coimbra, Portugal, Gago A ,   Rheumatology Department, Centro Hospitalar Lisboa  Ocidental, Lisbon, Portugal, Correia M ,   Rheumatology Department, Hospital  de Braga, Braga, Portugal, Fernandes AL ,   Rheumatology Department, Centro  Hospitalar Universitário do Algarve, Faro, Portugal, Dinis S ,   Rheumatology  Department, Unidade Local de Saúde da Guarda, Guarda, Portugal, Teixeira R ,   Rheumatology Department, Centro Hospitalar Tondela-Viseu, Viseu, Portugal, Silva SP ,   Rheumatology Department,  Centro Hospitalar do Baixo Vouga, Aveiro, Portugal; Aveiro  Rheumatology Research Center, Egas Moniz Health Alliance,  Aveiro, Portuga, Costa C ,   Rheumatology Department, Centro Hospitalar  Trás-os-Montes e Alto Douro, Vila Real, Portugal, Beirão T ,   Rheumatology  Department, Centro Hospitalar Vila Nova de Gaia/Espinho, Gaia,  Portugal, Furtado C ,   Rheumatology Department, Hospital do Divino Espírito  Santo, Ponta Delgada, Portugal, Abreu P ,   Rheumatology Unit, Unidade  Local de Saúde de Castelo Branco, Castelo Branco, Portugal, Khmelinskii N ,   Rheumatology Department, Centro Hospitalar  Universitário Lisboa Norte, Centro Académico de Medicina de  Lisboa, Lisbon, Portugal; Rheumatology Research Unit, Instituto  de Medicina Molecular, Faculdade de Medicina, Universidade de  Lisboa, Centro Académico de Medicina de Lisboa, Lisbon, Portugal
Published: October 2024

Objectives: We aimed to identify clinical and serological predictors of myositis in mixed connective tissue disease (MCTD). Methods: We performed a nationwide, retrospective, multicentre study including adult-onset MCTD patients fulfilling at least one of the following diagnostic criteria: Sharp’s, Kasukawa, Alarcón-Segovia, or Kahn’s. Univariable analysis was performed using Chi-square, Fisher exact, Student’s t or Mann-Whitney U tests, as appropriate. Multivariable analysis was performed using binary logistic regression. Results: Ninety-eight patients were included. Myositis was observed in 43.9% of patients, of whom 60.5% had myositis at disease onset. Proximal muscle weakness was described in 30 patients with muscle involvement (70%). Gastrointestinal involvement was identified in 28% and respiratory involvement in 29% of myositis patients. In the same subgroup of patients, 41.7% had a myopathic pattern on electromyography, and 47.1% had histological myositis features in the muscle biopsy. Fever (OR=6.96, p=0.022) was an independent predictor of myositis, regardless of sex, age at diagnosis, ancestry, and respiratory involvement. African ancestry (OR=8.39, p=0.019), leukopenia at the disease onset (OR 6.24, p=0.021), and younger age at diagnosis (OR=1.07/year, p=0.035) were identified as independent predictors of myositis at disease onset, regardless of sex and scleroderma pattern in capillaroscopy. Conclusions: Myositis is a common manifestation of MCTD, even at the disease onset. African ancestry, leukopenia at the disease onset, younger age at diagnosis, and fever should prompt a thorough evaluation for myositis.