Endocrine Abstracts

A 65-year-old lady who was known to hypothyroidism and was treated with Levothyroxine 100microgram once daily for more than 20 years presented to the endocrine clinic with symptoms and signs of thyrotoxicosis. Apart from Levothyroxine, she was taking over-the-counter multivitamins and Vitamin D. Visual fields were full to confrontation and there was no goitre. Thyrotoxicosis was confirmed biochemically and levothyroxine was stopped. Despite being off Levothyroxine for more than a few months, she remained clinically and biochemically thyrotoxic. TPO antibodies were positive and ultrasound thyroid showed coarse echotexture of thyroid gland suggesting chronic thyroiditis. She was treated with antithyroid drugs and became euthyroid. Hoshimotos and Graves’ disease are the two most common autoimmune thyroid problems. Conversion from thyrotoxic to hypothyroid state is common but vice versa is relatively rare. The exact aetiology is unknown but may involve autoimmune mechanisms. It is thought to be due to either switching of blocking TSH receptor antibodies (TRAb) to stimulating ones or predominant effect of TPO antibodies over stimulating TRAb when both antibodies (TPO and TSH receptor antibodies) are present. Clinicians should be mindful that patients with hypothyroidism can become thyrotoxic years down the line and hence regular monitoring of TFTs is required. Also, many such patients will require long term block and replacement antithyroid drugs to ensure fluctuations between stimulating and blocking antibodies does not significantly affect thyroid functional status or thyroid eye disease.