The place of JAK inhibitors in systemic juvenile idiopathic arthritis with lung disease (SJIA-LD): French experience.

Objectives: A new form of systemic juvenile idiopathic arthritis (SJIA) with associated lung disease (SJIA-LD) has recently been described. Multiple lines of treatment have failed to yield satisfactory results for this disorder. JAK inhibitors (JAKis) have recently been approved for the treatment of JIA, but clinical evidence of their efficacy in SJIA-LD is still weak. Here we describe and assess real-life experience of SJIA-LD treatment with JAKis in France.

Methods: This is a retrospective study based on information gathered from patients' medical records. Systemic and pulmonary symptoms, biological data including CRP, ferritin, IL18, chest CT scan, and functional respiratory tests were collected.

Results: Eight patients with SJIA-LD were identified in French pediatric rheumatology centers. All received at least one JAKi (baricitinib, ruxolitinib, and/or tofacitinib). Complete disease control was obtained in four patients. Steroids were tapered in four patients and stopped in two. Three patients presented an episode of MAS shortly after anti-IL1s were stopped when JAKis were introduced. Two patients had other serious side effects (viral reactivation-EBV, BK virus, cytopenia). At last follow-up, one patient had died from severe MAS, two patients had undergone hematopoietic stem cell transplantation, four were in complete response (two of them free of steroids), and one in partial response with JAKis. Lung response to JAKi was not clearly linked to disease duration.

Conclusion: JAKis offer another therapeutic option for patients with SJIA-LD. However, the risk of MAS argues for caution about stopping anti-IL1s when introducing JAKis. Tolerance needs careful monitoring in larger studies.