Challenging diagnosis of thyroid hormone resistance initially as Hashimoto's thyroiditis

Background: Resistance to thyroid hormone (RTH) commonly presents with goiter, attention deficit hyperactivity disorder (ADHD), short stature and tachycardia. However, due to its variable presentation with subtle clinical features, a third of the cases are mistreated, typically as hyperthyroidism. Case presentation: A 15-year-old female with ADHD and oligomenorrhea was initially diagnosed as Hashimoto's thyroiditis but found to have a rare heterozygous mutation in c803 C> G (p Ala 268 Gly) in the THR beta gene, confirming resistance to thyroid hormone. Conclusions: Fluctuating thyroid function tests in addition to thyroid peroxidase antibody (TPO Ab) positivity complicated the diagnosis of RTH, initially diagnosed as Hashimoto's thyroiditis. A high index of suspicion is needed to prevent misdiagnosis and mistreatment.