Endocrine Abstracts

Case history: A 52 year old lady presented to her GP with a 2 year history of headaches, anxiety and loose stools. The GP found lid retraction and fine tremor but no goitre. Her heart rate was 100. Her GP sent blood for thyroid function tests and results showed a TSH of <0.03 mu/l and free T3 of >30.8 pmol/l. She was started on propranolol 40mg thrice daily and referred to endocrinology. In clinic she described palpitations whilst watching TV and sweatiness. She had suspected she had lost weight over two years. She had no eye symptoms. Her only past medical history was depression and she was only on propranolol. Her sister and son had been diagnosed with Thyroid Hormone Resistance (THR). On examination she had mild smooth enlargement of her thyroid and no thyroid bruit. Her heart rate was 72 bpm. She had mild lid retraction and mild proptosis of her right eye with no diplopia. Her propranolol was decreased to 40 mg twice daily and she was started on carbimazole 30 mg once daily.

Investigations: TFTs on follow-up three months later in clinic demonstrated an improved T3 of 11.0 pmol/l and her TSH remained suppressed at <0.03 mu/l. Ultrasound of the thyroid showed overall appearance in keeping with Graves’ disease and an 8 mm nodule in the right lobe. A thyroid uptake scan showed borderline diffuse enlargement of the thyroid with diffuse symmetrical uptake throughout. Thyroid receptor antibodies were raised at 0.8 U/l (0–0.4). Alpha subunit levels were normal at 1.15 iu/l (0–3).

Results and treatment: The carbimazole dose was slowly titrated downwards and 4 years later was stopped. This lady’s symptoms settled within a few months of starting carbimazole. Her TSH rose into the reference range within 5 months of treatment starting and remained in range. Her free T3 remained elevated and seemed to respond to the changes in carbimazole dose, settling at ~10 pmol/l once treatment had finished. Her free T4 remained ~30 pmol/l throughout.

Conclusion and points for discussion: This lady has strongly suspected Thyroid Hormone Resistance (genetic testing results awaited) and this case demonstrates the challenges when THR presents alongside Graves’ disease. TSH at presentation was suppressed despite the THR due to the extreme thyroid hormone levels overcoming the thyroid hormone resistance. TFTs need to be taken in context and elevated levels accepted with the dosage of carbimazole titrated according to the patient’s symptoms.