Endocrine Abstracts

Case 1: A 32 year old fit and well female presented with symptoms of thyrotoxicosis and goitre. Her initial investigations revealed fT4 45 pmol/l (10–20) and fT3 26 pmol/l (3.5–6.5), with undetectable TSH. TSH receptor antibodies were positive. She was commenced on beta blockers and carbimazole and increased to 60 mg daily, with the fT4 improving only to 34.4 and fT3 to 13.8. Cholestyramine was commenced and titrated to a dose of 4 g twice daily, with resultant normalisation of free thyroid hormones levels. Vitamin D deficiency developed which was treated, but no coagulopathy. Planned thyroidectomy was reconsidered by the patient in view of the clinical response.

Case 2: A 39 year old male gave a history of Graves thyrotoxicosis 4 years earlier for which he was treated with carbimazole for 2 years before defaulting attendance. He represented with severe thyrotoxic symptoms affecting his physical, personal and professional life. Investigations showed fT4 61.6, fT3 29.4, TSH suppressed and TSH receptor antibodies positive. Despite 60 mg of carbimazole daily the fT4 improved only to 37.6 and fT3 to 16.4. Addition of cholestyramine was well tolerated and resulted in further improvements in thyroid hormone levels and considerable symptomatic improvement. Surgery is planned with Lugol’s iodine pretreatment.

Discussion: Cholestyramine is a bile acid sequestrant that is predominantly used in the treatment of cholestatic pruritus and dyslipidaemias. The thyrotoxic state leads to an increased enterohepatic circulation, and cholestyramine can bind to thyroid hormones and lead to their increased excretion via the intestinal system. These two cases illustrate its clinical utility as a well tolerated adjunct to thionamides in severe thyrotoxicosis, and its use can buy time for more considered long term management.