Baricitinib in the Treatment of New-onset Juvenile Dermatomyositis (MYOCIT)

Inclusion Criteria:

• Patient aged 3-18 years with new-onset juvenile dermatomyositis, according to the ENMC 2018 dermatomyositis classification criteria

• Muscle weakness at MMT and/or CMAS (MMT < 74 and/or CMAS < 45)

• Seropositivity or vaccination for chickenpox

• For patients of childbearing age (following menarche) : Negative βHCG and effective method of contraception (sexual abstinence, hormonal contraception, intrauterine device or hormone-releasing system, cap, diaphragm or sponge with spermicide, condom) until the 7 days after administration of the last dose of Baricitinib

• Informed consent form signed by the patient or child' s parents Patient affiliated to a social security regime

Exclusion Criteria

• Amyopathic dermatomyositis (without muscle weakness)

• Inability to be treated by oral way or to take pills

• Previous treatment with JAK inhibitor

• Previous treatment of JDM with immunosuppressive drugs or biologics other than corticosteroids. Previous treatment with prednisone was allowed for no more than 1 month.

• Previous history of cancer

• Live vaccine within the 4 weeks before starting baricitinib therapy

• Current, or recent (< 4 weeks prior to baseline) of active infections according to investigator appreciation, but necessarily, including HBV, HCV, HIV, tuberculosis.

• Positive blood CMV PCR

• Creatinine clearance < 40 ml/min

• Lymphocytes < 0,5x109 cell/L and Neutrophils < 1x109 cell/L

• Hemoglobin < 8 g/dL

• Symptomatic herpes herpes simplex infection within 12 weeks prior to inclusion

• History of thrombosis or considered at high risk of venous thrombosis by the investigator

• Presence of severe JDM-related involvements: cardiovascular (requiring vasopressive drug and/or intensive care unit), respiratory (requiring oxygen and/or intensive care unit), gastrointestinal (requiring abdominal surgery).

• History of severe non-related JDM involvement: cardiovascular, respiratory, hepatic, gastrointestinal, endocrine, hematological, neurological or neuropsychiatric disorders or any other serious and/or instable illness that, in the opinion of the investigator, could constitute an unacceptable risk, when taking baricitinib.

• Actual or in project of pregrancy and breast-feeding until the 7 days after administration of the last dose of Baricitinib

• Patient on AME (state medical aid)

• Participation in another interventional study involving human participants or being in the exclusion period at the end of a previous study involving human participants