Response to Hydroxychloroquine in Immune Thrombocytopenia in Childhood-Onset Systemic Lupus Erythematosus

Objectives The management of immune thrombocytopenia in childhood-onset systemic lupus erythematosus (cSLE) is not standardized. We examined the efficacy and safety of hydroxychloroquine (HCQ) as monotherapy for thrombocytopenia in cSLE.[1] Methods We retrospectively reviewed the medical records of patients who developed thrombocytopenia (platelet count < 100 ×10^9/L) and were diagnosed with cSLE and followed in the rheumatology clinic at The Hospital for Sick Children (SickKids) between January 2005 and December 2024. In this clinic, structured data, including disease activity (assessed by the Systemic Lupus Erythematosus Disease Activity Index (SLEDAI)), are prospectively collected at every visit. Definite cSLE was defined by the 2019 EULAR/ACR classification criteria, while patients with incipient cSLE had clinical features of evolving SLE but achieved a EULAR/ACR score below 10. A complete response was defined as a platelet count >100 ×10^9/L with no bleeding. Partial response was defined as a platelet count >30 ×10^9/L with at least a 2-fold increase from the lowest count and no bleeding. Descriptive statistics were used to characterize the study groups and outcomes. Results Of the 798 patient records reviewed, 207 (26%) of patients had thrombocytopenia. One hundred sixty-one patients (78% female) with a median age of 12.7 years (IQR 10.1-14.5) and a median platelet count of 22 ×10^9/L (IQR 7-59) at the time of thrombocytopenia diagnosis were included (Figure 1).[1] The median lowest platelet count was 11 ×10^9/L (IQR 2-41). 131 patients (81%) had definite, and 30 (19%) had incipient cSLE (Table 1). One hundred nine (67%) of patients were treated with corticosteroids, and 80 (50%) of them received IVIG prior to commencing on HCQ (Table 2). Seventy-three (45%) patients achieved complete or partial responses before initiating HCQ. 147 (91%) patients were treated with HCQ, initiated at a median of 6 months (IQR 2.7-12.2) after thrombocytopenia diagnosis, at a median platelet count of 77 × 10^9/L (IQR 32.5-198.0). Of those, 35 (24%) patients were treated with HCQ monotherapy (Table 3). All 35 responded; 30 had complete responses after a median follow-up of 52 months (IQR 33-75). Of the 147 patients who received HCQ during their disease course, 11 experienced side effects, and 7 of them had to discontinue the treatment due to these effects. Conclusion While most patients initially required additional treatments, HCQ monotherapy effectively maintained a partial or complete response in thrombocytopenia for over 4 years in approximately 1 in 5 cSLE patients. References [1.] Khellaf M. Am J Hematol 2014;89:194-8.