Excellent response to treatment with hydroxychloroquine in pediatric patients with SLE-related immune thrombocytopenia

Background: Pediatric immune thrombocytopenia (ITP) may precede systemic autoimmune disorders. In adolescent patients with ITP, routine screening for systemic lupus erythematosus (SLE) may be performed by testing for antinuclear antibody (ANA) titer. Hydroxychloroquine (HCQ) is a safe and effective immunomodulatory drug in patients with SLE but rarely used in ITP. We analyzed the platelet count response and safety of HCQ in treating pediatric patients with SLE-related ITP. Methods: A retrospective study including pediatric patients with ITP and definite or incomplete SLE, who were treated with HCQ during 2010-2021. SLE was defined by ANA titer >= 1:160 as measured by immunofluorescence and >= 10 points according to the 2019 EULAR/ACR 2019 classification criteria, while patients with incomplete SLE achieved a score < 10. Complete response (CR) of the platelet count was defined as platelet count > 100 x 109/L; partial response (PR) as platelet count 30-100 x 10(9)/L and exceeding >= twice baseline counts. Results: Of the 17 patients included (median age 15.5 years; IQR 3.6), 15 (88.2%) were female, 13 had definite SLE, and four had incomplete SLE. HCQ was initiated at a median of 17 months after ITP diagnosis with a median platelet count of 38 x 10(9)/L (IQR 28). At 8 weeks, 8 (47.1%) patients responded, including 6 (35.3%) achieving CR. After one year, the overall response was 82.4%, with the remaining patients having stable platelet counts requiring no additional ITP therapy. The response was maintained at a median follow-up of 42 months. No adverse effects to HCQ were noted. Conclusion: Pediatric patients with SLE-related ITP may benefit from treatment with HCQ.