IFIH1 and dermatomyositis: Among patients with DM-RPIP, for those with any of the poor prognostic factors of anti-MDA5 Ab-positivity, serum ferritin ≥ 600 ng/ml plus AaDO2 ≥ 45 mmHg, or serum LIGHT ≥ 120 pg/ml, combined administration of prednisolone at 1 mg/kg/day and calcineurin inhibitor (CSA C2 level or TAC trough level adjusted to ≥ 1500 ng/ml or 10–20 ng/ml, respectively), and aggressive additional doses of IVCY are recommended as soon as possible after diagnosis.