Endocrine Abstracts

The conversion of Hashimoto thyroiditis (HT) to hypothyroidism is frequently observed in daily clinical practice, but the development of Grave’s disease (GD) after long-standing hypothyroidism is rare and intriguing. A 70-year-old woman visited an endocrinologist, complaining of increased heart rate, anxiety, and a feeling of discomfort in the neck. Past medical history revealed HT with hypothyroidism. Laboratory tests showed significantly increased thyroid-stimulating hormone (TSH) and positive anti-thyroid peroxidase antibodies. Replacement therapy with levothyroxine 100 µg daily was initiated and implemented for approximately ten years. During the annual follow-up, thyroid hormones were found to be in the normal range. The recent physical examination revealed a firm and slightly enlarged thyroid. TSH suppression was detected, the peripheral thyroid hormone concentration and thyroid-stimulating hormone receptor antibodies (TRAB) were seen to have increased. Neck ultrasound showed slight thyroid hypoechogenicity and non-homogeneity due to multiple hypoechogenic zones. Sonographically, the thyroid lesions were indicative of chronic thyroiditis. Overactive thyroid was suspected. Therefore, levothyroxine was gradually withdrawn. Six months later, hyperthyroidism was seen to have persisted and, ultimately, required anti-thyroid treatment. This case demonstrates a rare case of HT converting to GD. We suggest that the possibility of conversion from hypothyroidism to hyperthyroidism should be considered even if there is long-standing hypothyroidism. We propose measuring TRAB in suspected cases. Further studies are needed to confirm this proposal.