Myositis-specific autoantibody subtypes are associated with response to Janus kinase inhibitors in patients with juvenile dermatomyositis.

OBJECTIVES

To evaluate the efficacy and safety of Janus kinase inhibitors (JAKi) in a monocentric series of patients with JDM and to identify factors associated with the achievement of clinically inactive disease (CID).

METHODS

Single-centre retrospective study of 39 JDM patients treated with JAKi for at least 6 months. The proportion of patients achieving CID within 6 months after initiation of JAKi was assessed using the PRINTO criteria and the Skin Disease Activity Score. Type 1 IFN gene signature, serum IFN-α and IFN-β protein titres were measured as potential response biomarkers.

RESULTS

Thirty-nine patients with JDM were included. Partial or complete CID was achieved in 32/39 (82%) patients after 6 months of treatment. In responders, the mean steroid dose decreased from 1 to 0 mg/kg/day (P = 0.001) and all other medications were withdrawn. In multivariable analysis, the presence of anti-transcriptional intermediary factor 1 gamma (anti-TIF1γ) Abs was the only factor at JDM onset associated with the absence of CID (P < 0.001). A significant decrease in the median Type 1 IFN score and serum IFN-α from the diagnosis of JDM to the 6-month follow-up was observed only in patients with CID. JAKi-related adverse events consisted of infections in nine patients (including five herpes zoster infections) and weight gain in three patients.

CONCLUSIONS

JAKi induced CID in the majority of new-onset and refractory JDM patients, except in a subset of patients with refractory TIF1γ-positive JDM. Overall tolerance was acceptable. These results need to be validated in a larger prospective international cohort study.