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<p>Resistance to thyroid hormone beta (RTHβ) is a rare genetic disorder characterized by reduced tissue responsiveness to thyroid hormones despite elevated circulating levels. The coexistence of RTHβ and ectopic thyroid tissue is exceptionally rare and presents significant diagnostic and management challenges. We report an eight-year-old girl diagnosed with congenital hypothyroidism through neonatal screening, with thyroid scintigraphy demonstrating a lingual ectopic thyroid. Levothyroxine maintained free thyroxine within the upper reference range and clinical euthyroidism; however, biochemical control as judged by TSH was persistently suboptimal. Genetic sequencing identified a heterozygous <i>THRB</i> c.1312&#xa0;C &gt; T (p.Arg438Cys) mutation, confirming RTHβ. At seven years of age, the patient developed progressive sublingual swelling with markedly elevated thyroglobulin levels. Positron emission tomography demonstrated metabolic activity consistent with functioning thyroid tissue. Surgical excision was undertaken after multidisciplinary discussion in view of progressive enlargement and chronic TSH stimulation. Histopathology revealed benign hyperplastic thyroid tissue, and <i>BRAF</i> mutation testing was negative. The patient remains clinically stable on levothyroxine replacement. This case highlights the diagnostic delay that may occur when RTHβ coexists with congenital hypothyroidism due to ectopic thyroid, and underscores that persistent unexplained TSH elevation despite clinical euthyroidism on levothyroxine should prompt reassessment for RTHβ even when an alternative diagnosis is established.</p>

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Lingual thyroid and resistance to thyroid hormone beta due to a novel THRB c.1312 C > T mutation in a child: diagnostic pitfalls and management

  • 期刊论文

  • 发表日期：

    2026年6月2日

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  • Mohammad Hosny Awad,
  • Nandu Thalange,
  • Mohamed El Abiary

摘要

Resistance to thyroid hormone beta (RTHβ) is a rare genetic disorder characterized by reduced tissue responsiveness to thyroid hormones despite elevated circulating levels. The coexistence of RTHβ and ectopic thyroid tissue is exceptionally rare and presents significant diagnostic and management challenges. We report an eight-year-old girl diagnosed with congenital hypothyroidism through neonatal screening, with thyroid scintigraphy demonstrating a lingual ectopic thyroid. Levothyroxine maintained free thyroxine within the upper reference range and clinical euthyroidism; however, biochemical control as judged by TSH was persistently suboptimal. Genetic sequencing identified a heterozygous THRB c.1312 C > T (p.Arg438Cys) mutation, confirming RTHβ. At seven years of age, the patient developed progressive sublingual swelling with markedly elevated thyroglobulin levels. Positron emission tomography demonstrated metabolic activity consistent with functioning thyroid tissue. Surgical excision was undertaken after multidisciplinary discussion in view of progressive enlargement and chronic TSH stimulation. Histopathology revealed benign hyperplastic thyroid tissue, and BRAF mutation testing was negative. The patient remains clinically stable on levothyroxine replacement. This case highlights the diagnostic delay that may occur when RTHβ coexists with congenital hypothyroidism due to ectopic thyroid, and underscores that persistent unexplained TSH elevation despite clinical euthyroidism on levothyroxine should prompt reassessment for RTHβ even when an alternative diagnosis is established.