Pituitary resistance to thyroid hormone caused by a novel mutation (H435A) in the thyroid hormone receptor beta: A...

In patients with pituitary thyroid hormone resistance, the ability of the pituitary gland to detect (and down-regulate) the increase of triiodothyronine is selectively impaired, while the periphery remains sensitive to triiodothyronine levels, producing symptoms of peripheral thyrotoxicity. Subsequently, there is no feedback of pituitary production of thyroid-stimulating hormone (TSH), which is responsible for this hyperthyroidism.

We report a case of a 46-year-old Chinese woman diagnosed with a thyroid nodule, with normal thyroid function. She underwent conventional subtotal thyroidectomy, and replacement therapy (levothyroxine) was used for as convention. However, it was later proven that she had pituitary resistance to thyroid hormone, as supra-physiological doses of levothyroxine were required to normalize TSH levels, which resulted in peripheral thyrotoxicity.

Based on the patient's symptoms, laboratory tests results, imaging examinations, and genetic analysis (which noted a gene mutation), a diagnosis of pituitary resistance to thyroid hormones was confirmed.

The dose of levothyroxine was adjusted periodically and β-adrenergic blocker was used as symptomatic treatment.

The outcome in the reported case has been satisfactory despite the persistence of non-suppressed TSH.

An inappropriate level of TSH should always be evaluated. We found a new mutation (H435A) of the thyroid hormone receptor beta gene, which allowed for the establishment of a definitive diagnosis.