Endocrine Abstracts

A 30-year-old gentleman presented with non-specific symptoms of tiredness and lethargy persisting over many years. Initial private TFTs in 2021 revealed a normal TSH of 2.29 mIU/l and elevated FT4 at 39.4 pmol/l. Repeat testing by his GP showed similar results (TSH 1.85, FT4 39.3, and free T3 9.3 pmol/l). Due to these abnormal thyroid function results and ongoing symptoms, he was referred to Endocrinology for further assessment. The patient reported no hyperthyroid symptoms such as weight loss, fever, increased sweating, neck pain / swelling, tremor, or palpitations. His medical history was unremarkable, with no medications except for past smoking cessation 10 years prior. Family history included multiple sclerosis in his mother only. On examination, he was euthyroid with no goitre and no Thyroid Eye signs. Given the discordant TFT results and clinical euthyroidism, an alternative assay at Leeds confirmed elevated thyroid hormones (TSH 2.0, FT4 35, FT3 11 pmol/l). The patient led an active lifestyle as a fitness enthusiast, frequenting the gym 4–5 times weekly, and had a physically demanding occupation. He regularly took creatine, multivitamins, and minerals, which were discontinued for 6–8 weeks to exclude assay interference. Repeat TFTs remained unchanged (TSH 1.85, FT4 39.3, FT3 9.3). Subsequently, a thyrotropin-releasing hormone (TRH) stimulation test was performed with the following results: The exaggerated rise in TSH following TRH administration strongly suggests a diagnosis of thyroid hormone resistance (THR) rather than a TSH-secreting pituitary adenoma (TSHoma), which typically shows a blunted TSH response. The patient exhibited no clinical signs of pituitary disease, lowering suspicion for TSHoma. Given his euthyroid status and absence of symptoms, no thyroid hormone treatment was initiated. This case exemplifies the diagnostic challenges in thyroid hormone excess with non-suppressed TSH and highlights the utility of the TRH test in differentiating THR from TSHoma

Conclusion: • The TRH test showed a clear, exaggerated TSH rise, which strongly favors THR over TSHoma. • The lack of pituitary symptoms or clinical suspicion lowers the pre-test probability of TSHoma. • MRI and alpha-subunit measurement remain options if the clinical or biochemical picture changes or if there is diagnostic uncertainty. • This approach aligns with a targeted, cost-effective diagnostic strategy minimizing unnecessary tests. • Will continue clinical and biochemical monitoring to catch any evolution.