Janus kinase inhibitors therapy in idiopathic inflammatory myopathies: a case series

To evaluate the clinical response of Janus kinase inhibitors (JAKi) across subtypes of idiopathic inflammatory myopathies (IIM) in a cohort of patients with refractory disease.

We conducted a retrospective analysis of all adult IIM patients treated with JAKi at our centre. Treatment response was assessed based on changes in muscle strength, serum biomarkers of muscle damage and inflammation, pulmonary function, radiological evolution of interstitial lung disease (ILD) and corticosteroid dosage.

Ten IIM patients who were previously or currently receiving JAKi therapy were identified. Six patients were female and the mean age was 52.7 years (standard deviation [SD] 13.91). Anti-synthetase syndrome was the most common subtype (n=5, 50%). At baseline, median manual muscle test 8 score was 136 (interquartile range [IQR] 25.5) and, after therapy, was 147 (IQR 8), representing a statistically significant increase (p<0.05). Corticosteroid dose reduction was also statistically significant (p<0.05), with the median daily dose decreasing from 10mg to 2.5mg. Additionally, four patients were able to discontinue corticosteroid therapy. In six patients with ILD, diffusion capacity for carbon monoxide improved significantly (p<0.01), from 68.33% (IQR 19.31) to 93% (IQR 7.27). No significant changes were observed in serum inflammatory markers, creatine kinase, forced expiratory volume first second or forced vital capacity.

JAKi therapy appears to be clinically effective, well tolerated, and safe in patients with refractory IIM, with a particular benefit in ILD. The steroid sparing effect was also a major outcome. Future prospective and controlled studies are warranted to confirm these preliminary results and better define the therapeutic potential of JAKi in IIM.