case_images: PMC11131390_01
case_images: Thyroid function tests and antithyroid drug treatment from the diagnosis to the onset of hypothyroidism.. CBZ, carbimazole; T4, thyroxine; TRAbs, TSH receptor antibodies; TSH, thyroid-stimulating hormone.
case_images: 10.1177_20420188241256470-fig1.jpg
case_images: PMC11131390_01_10.1177_20420188241256470-fig1.jpg
case_images: fig1-20420188241256470
case_images: The first follow-up off CBZ in August 2017, the patient was euthyroid with TSH = 3.3 microIU/L, free T4 = 1.17 ng/dL, and TRAbs was 3.3 IU/L. In November 2017, 4 months after stopping CBZ, the patient presented with 4 kg weight gain (67-71 kg) and severe biochemical hypothyroidism, TSH = 73.5 microIU/L and free T4 = 0.35 ng/dL, which was repeatedly confirmed, TSH = 48.9 microIU/L and free T4 = 0.66 ng/dL (Figure 1). Considering the patient age (66 years) and body weight (71 kg), the patient was started on replacement therapy in the form of levothyroxine 75 microg/day (calculated as 1.1 microg/kg/day), and the dose was later titrated to achieve a target TSH of 0.3-3 microIU/L, which was finally achieved using 100 microg/day, and this target was maintained for 45 months (July 2019-April 2023). TRAbs were measured in November 2021, and it was negative at <0.8 IU/L. The coincidence of quitting smoking in July 2017 and the spontaneous development of overt hypothyroidism in November 2017, only 4 months later, urged us to search for a possible link between quitting smoking and new onset hypothyroidism in patients with treated GD.