Ruxolitinib Treatment in Inclusion Body Myositis

Inclusion Criteria: * Age ≥ 45 years * Effective contraception for the duration of the clinical trial for fertile women of childbearing age * Defined diagnosis of IBM according to data-derived criteria (Llyod et al, 2014): Patient must fulfill the three following criteria for being diagnosed as IBM: (1) finger flexor or quadriceps weakness; and (2) muscle biopsy showing endomysial inflammation; and (3) muscle biopsy showing invasion of nonnecrotic muscle fibers or rimmed vacuoles * To be able to walk 6 min without assistance from another person (external assist devices permitted \[e.g., canes, walkers, or rollators\]) * Patient informed and having signed the consent for participation, possibly assisted by a trusted person Exclusion Criteria: * Pregnancy or breastfeeding * Patient under guardianship, curatorship, safeguard of justice or deprived of liberty * Patient with cognitive disorders or unable, according to the investigator, to understand the study and/or to give informed consent * Quadriceps weakness (manual muscle testing, MRC) below or equal 1 * Forced vital capacity (FVC) or forced expiratory volume (FEV) \< 50% of predicted value * Concomitant use of immunomodulatory drugs including previous treatment with JAK inhibitor, or medications acting on muscle anabolism or catabolism * Live vaccine within the 4 weeks before starting treatment * Comorbidity or active chronic disease which contraindicate ruxolitinib: * Lipid parameters abnormalities/elevations * Seve…