Endocrine Abstracts

Case report: A 76-year-old lady was referred to our Endocrinology department due to general malaise and abnormal thyroid function tests: TSH 1.1 (0.3–4.2) mU/l, fT₄ 30.6 (12.0–23.0) pmol/l, fT₃ 8.3 (4.0–7.8) pmol/l. She had received ¹³¹I twice, 16 and 36 years previously, at different hospitals for presumed thyrotoxicosis. She was clinically euthyroid and had a small diffuse goitre.

Repeat thyroid function tests at our lab and 2 other labs using different kits showed similar results, excluding the antibody assay interference. Thyroid microsomal antibodies and TBII were negative.

Hence a differential diagnosis between TSHoma and THR (thyroid hormone resistance syndrome) was sought. Anterior pituitary endocrine profile was unremarkable. Alpha subunit and SHBG were in the normal range. There was a 6 fold increment in TSH on TRH test. Pituitary MR scan did not show any pituitary abnormality. Investigations thus suggested a diagnosis of THR. This was confirmed by measuring thyroid function tests in the patient’s two sons one of whom showed a similar pattern. We thus made a diagnosis of euthyroid generalised THR and did not offer her specific treatment.

Discussion: This case serves as a reminder that the assessment of clinical thyroid status is vital in order to make the correct diagnosis and avoid inappropriate treatment. The case highlights the differential diagnosis of elevated free thyroid hormone levels in conjunction with a non-suppressed TSH, which can occur due to assay interference with heterophile antibodies, TSHoma or thyroid hormone resistance syndrome.