Endocrine Abstracts

Introduction: An intrinsic relationship exists between the thyroid gland and diabetes mellitus, alongside their respective treatments. We report a patient with type 2 diabetes mellitus and hypothyroidism on levothyroxine who developed clinical (and biochemical) hyperthyroidism following the initiation of a subcutaneous semaglutide, requiring a dosage reduction in levothyroxine.

Case Report: A 56-year-old female with type 2 diabetes mellitus and hypothyroidism on 100 micrograms of levothyroxine is seen at the clinic. Her thyroid-stimulating hormone (TSH) level increased on two separate visits (4.80→11.30 mIU/l) five months apart, for which levothyroxine is increased to 125 micrograms (TSH 1.020 mIU/L five months later). Subcutaneous semaglutide is introduced to treat her body mass index of 41 kg/m² and HbA1c (7.3%). At follow-up, she demonstrated clinical and biochemical hyperthyroidism, with weight loss of 39 pounds, sweating, and palpitations (TSH <0.005 mIU/l). Following a reduction of her levothyroxine to 100mcg, her symptoms abated and TSH normalised.

Discussion: The dosage of levothyroxine for hypothyroidism is weight-based; as depicted, with weight loss, the need for a potential decrease in the dosage, to prevent untoward hyperthyroidism, should be anticipated. This pathophysiological basis is not entirely understood but is believed to occur via two mechanisms: (1) changes in absorption from delayed gastric emptying; (2) secondary to weight loss imposed by semaglutide.

Conclusion: The relationship between the thyroid and diabetes mellitus is not entirely understood. Moreover, the medications used for either disorder appear to affect (positively/negatively) one another. Due to the scarcity of data, our case is presented to highlight this phenomenon and remind clinicians of the potential for iatrogenic hyperthyroidism in such a cohort.