Endocrine Abstracts

Background: Graves’ disease and Hashimoto’s thyroiditis are the most common autoimmune thyroid conditions. Hyperthyroidism following hypothyroidism is a rare phenomenon. Hypothyroidism was once thought to be a permanent state requiring lifelong replacement therapy but we have noted that there are increasing numbers of cases which are against this postulation. We would like to report 3 cases initially diagnosed with hypothyroidism and referred to us following development of hyperthyroidism in recent times.

Case 1: 84-year-old lady with clinical and biochemical hypothyroidism in 2017, initiated on levothyroxine therapy, presented with hyperthyroid symptoms in 2020 confirmed by laboratory testing and strongly positive TSH receptor antibody.

Case 2: 66-year-old lady, diagnosed with hypothyroidism in 1998, was initiated on thyroxine developed hyperthyroid symptoms in 2018 leading to stopping levothyroxine therapy. She was treated with Carbimazole for 18-months following which she developed hypothyroidism needing Levothyroxine.

Case 3: 51-year-old lady was diagnosed and treated as hypothyroidism from 2015. She developed hyperthyroidism and ophthalmopathy in 2018. She then had Carbimazole therapy, followed by near-total-thyroidectomy in 2019.

Conclusions: The pathophysiology behind the fluctuating thyroid biochemistry is poorly understood. One involves switching of TSH-receptor-blocking-antibodies (TSAb) and TSH-receptor-stimulating-antibodies (TBAb) resulting in hypothyroid and hyperthyroid phase respectively, causing a push-pull effect. Second is initial autoimmune thyroid damage causing underactivity of thyroid followed by the recovery phase where the stimulating antibodies would lead to a hyperactive state. Conversion of hypothyroidism to hyperthyroidism may not be as rare as we have previously thought. The underlying mechanism is still not clear, needing more research in this area. Having this knowledge and awareness will guide the clinicians to suspect the fluctuation in the condition earlier, stop thyroxine timely and counsel patients better about the potential uncertain natural course of the disease.