Is There a Need to Look for Antithyroid Antibodies in Children With Immune Thrombocytopenia?

Abstract

To the Editor: I read with interest the paper on polyautoimmunity in childhood immune thrombocytopenia (ITP) by Kamioka et al1 but I would like to challenge the suggestion of looking for antithyroid antibodies in children with otherwise uncomplicated ITP outside a research setting. Our experience and data from the published literature do not support a prognostic value of antithyroid antibodies in the management of ITP. There were 78 consecutive children diagnosed with ITP in the author’s institution from 2007 to 2015.2 Fifteen (19.2%) had chronic ITP at 1 year after diagnosis. Tests for antinuclear antibody, direct antiglobulin test, antithyroglobulin (Tg-Ab,) and antithyroperoxidase (TPOAb), were done in children with chronic ITP annually. Two (14.3%) of them were found to be positive for both Tg-Ab and TPO-Ab on first testing, and they were negative for other autoantibodies. Case 1 was a female first diagnosed at 71⁄2 years of age with platelet of 77×109/L.3 Her TgAb (131.2 IU/mL, normal <34.0) and TPO-Ab (54.1 IU/mL, normal <12.0) were both elevated. She received intermittent intravenous immunoglobulin during the first 3 years of follow-up, and had since been free from bleeding or treatment. At 71⁄2 years after diagnosis, her platelet was 44×109/L, Tg-Ab (215 IU/mL) remained positive while TPO-Ab antibody had disappeared. Case 2 was a female first diagnosed at 71⁄4 years of age with platelet of 15×109/L. Tg-Ab was 388.50 IU/mL and TPO-Ab was 249.33 IU/mL. As she had frequent epistaxis, treatment with eltrombopag was commenced during the second year of the illness and her platelet count had been maintained between 50 and 100×109/L since then. Her last autoimmune screen showed Tg-Ab 382.23 IU/mL and TPOAb 1170.29 IU/mL at 51⁄2 years after diagnosis. Both children remained euthyroid clinically and biochemically. The are 3 other case series on childhood ITP and thyroid disorders in the literature.4–6 Like Kamioka and colleagues publication, they were crosssectional studies with relatively short follow-up. Pooling all their data and ours together, there were 189 children diagnosed with chronic ITP. Almost twothirds of the subjects were female (96/148 or 64.9%). Their mean age was 8.0 (range: 0.5 to 17.0) years. Twenty-nine (15.3%) were tested positive for antithyroid antibodies. As reviewed by Giordano et al,7 the presence of antithyroid antibodies in children with ITP does not predict chronicity or response to treatment. Most of them were clinically and biochemically euthyroid while 2 needed treatment with thyroxine. One of these 2 patients was described as having overt hypothyroidism.4 The patient reported by Kamioka et al1 had signs of thyroiditis with grossly elevated serum thyroid stimulating hormone (71.05 μU/mL; normal <4.9). Thus, while antithyroid antibodies are common among children with chronic ITP, hypothyroidism affects only 1% of them and there were other clinical findings to suggest its presence. Routine screening for antithyroid antibodies in children with ITP may only generate anxiety with doubtful significance in predicting disease severity, chronicity, and later development of thyroid disorders. Prospective studies with longer follow-up are needed to answer these questions.