Background
Immune thrombocytopenia (ITP) is an immune-mediated disorder characterized as isolated thrombocytopenia. The incidence of ITP has been estimated at 1.0 to 6.4 per 100000 children annually.1, 2 About 20-30% of patients with ITP will progress to chronic disease.3 Chronic ITP is defined as ITP lasting for more than 12 months. Children with chronic ITP who require treatments may have a disappointing response to the first-line treatments (including corticosteroids and intravenous immunoglobulin (IVIG)) or a high rate of relapse after withdrawal of medication. For individuals who don’t respond to the first-line therapy, treatment with rituximab, thrombopoietin receptor agonist (TPO-RA), splenectomy, or other immunosuppressive drugs is required, and combination therapy can be considered in some contexts.
Hydroxychloroquine (HCQ), originally an antimalarial drug, can accumulate in lysosomes and alkalinize them, inhibiting their functions and interfering with metabolic and immune pathways.4This medication has been proved effective in treating some autoimmune diseases, such as systemic lupus erythematosus (SLE) and antiphospholipid syndrome.5, 6 Based on its effect on immunomodulation, some researchers applied it in the treatment of ITP and found that it may be effective in increasing platelet counts, especially for those with positive antinuclear antibody (ANA) or SLE associated ITP.7-9 However, the mechanism of HCQ in modulating platelet counts is not certified. And the association between its effect on platelet counts and ANA positivity is unclear.
ANA, a common marker of autoimmune diseases, can be present in children with ITP. Previous studies have reported a different response to medication between patients with positive ANA and those without.10-12 Determining whether ANA can be considered a biomarker for predicting the efficacy of HCQ on platelet counts will facilitate the reasonable application of HCQ. Here, we conducted a retrospective cohort study to assess the efficacy of HCQ in children with chronic ITP and to explore the interaction effect of ANA on the efficacy of HCQ.