An Incidental Finding of Elevated Thyroid Hormones; Everything You Need to Know About Interpreting Thyroid Function Tests - הכינוס השנתי של החברה הישראלית לפדיאטריה קלינית

נועה שפר-אברבוך ^1,2,3 Liora Lazar ^1,2 Ariel Tenenbaum ^1,2 Monica Franca ⁴ Moshe Phillip ^1,2 Liat de Vries ^1,2

¹The Jesse Z. and Sara Lea Shafer Institute for Endocrinology and Diabetes, National Center for Childhood Diabetes, Schneider Children’s Medical Center of Israel, Petah Tikva, ישראל
²Sackler Faculty of Medicine, Tel Aviv University, Tel Aviv, Israel, ישראל
³Raphael Recanati Genetics Institute, Rabin Medical Center, Beilinson Campus, Petah Tikva, Israel, ישראל
⁴Endocrinology Laboratory, The University of Chicago, South Maryland Avenue, Chicago, Il, ארצות הברית

Background: Thyroid functions are being tested often in the pediatric population for different reasons. Thyroid abnormalities might be false, transient or chronic. Simple algorithms to interpret thyroid functions will be displayed and an intriguing case will be presented.

Case presentation: A previously healthy five-year-old boy was found to have elevated FT4 and FT3 with a normal TSH, in a routine workup. He had no symptoms or signs of hyperthyroidism. According to the possible differential diagnosis, further workup was performed. Thyroid functions were similar using different platforms. Anti-thyroglobulin, thyroid peroxidase and thyroid receptor antibodies were negative. Parents and siblings were found to have normal thyroid functions. To rule out a TSH-secreting adenoma, performance of a brain MRI and a TRH test were considered. Genetic testing was performed instead.

Results: The proband was found to have a de novo mutation in one allele of the THRB gene, coding for part of the thyroid hormone receptor. The missense mutation, previously described in 10 families, reduces the binding affinity for T3 to 25% that of the normal receptor.

Conclusion: Thyroid hormones abnormalities are a common finding in the pediatric population. A specific work-up should be performed according to the abnormality. Resistance to thyroid hormones should be considered in the differential diagnosis of patients with non-autoimmune hyper-thyrotropinemia. Most patients are asymptomatic and elevated thyroid hormone levels can be an incidental finding. A fast genetic diagnosis can help avoid unnecessary, costly and complicated work-up, unnecessary treatment and of course enables appropriate follow-up and genetic family counseling.