Idiopathic inflammatory myositis (IIM), also known as myositis, are a heterogeneous group of diseases characterized by chronic inflammation of striated muscles and skin, with different clinical manifestations, treatment responses, and prognosis. This project will build a clinical follow-up cohort for idiopathic inflammatory myositis (IIM) centered on Renji Hospital, Shanghai Jiao Tong University School of Medicine, to promote the clinical and pathogenesis of this group of diseases.

Inclusion Criteria:Subjects must meet the following criteria for inclusion in this study: meet the 2017 EULAR/ACR classification criteria for inflammatory myopathy (IIM) or the 2018 ENMC-DM classification criteria (see above), plus:

1. Age≥ 18 years old and ≤ 75 years old

2. Meet the 2017 EULAR/ACR classification criteria for inflammatory myopathy (IIM), the above score ≥ 5.5 points if there is no muscle biopsy, and 6.7 points ≥ if there is muscle biopsy

3. Cooperate with follow-up, examination and treatment and voluntarily sign the informed consent form.

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   Exclusion Criteria:Potential subjects who meet the inclusion criteria will be excluded if they meet any of the following criteria:

   a. IIM with other connective tissue diseases; b. Negative myositis antibody test; c. Those who are in the period of acute infection, or have a history of active tuberculosis in the past; d. People with allergies or allergies to multiple drugs; e. Those who have mental illness or other reasons and cannot cooperate with examination, follow-up or treatment; f. Women who are pregnant, or are trying to become pregnant; g. Those who are participating in or have participated in clinical trials within the specified time.

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Aged 18-75 years and eligible for the 2017 European League Against Rheumatism/American College of Rheumatology.