Endocrine Abstracts

Background: Levothyroxine (LT4Rx) is one of the most prescribed drugs worldwide the vast majority of patients receive long-term treatment. However, in a recent study of 291 subjects, it was found that 60% were euthyroid 2 months after LT4-Rx discontinuation¹.

Aim of the study: A prospective clinical cohort follow-up study was carried out. In 688 subjects (82% females) aged 48.01±15.96 (range 17-84years) with 8.59±6.98 years on LT4Rx without a solid diagnosis of hypothyroidism, treatment was abruptly interrupted. The indications for treatment were nodule(s) (33%), undefined (27%), post-partum (7%) and Hashimoto’s thyroiditis (33%). A short period of follow-up was initiated in 54% of subjects (≤ 4 months, Group A) and long-term follow-up in the rest (up to 60 months, Group B). The subjects were evaluated when LT4Rx was discontinued, 2-4 months later, and at the end of follow-up. At each time point, estimation of TSH, FT4 levels, and thyroid ultrasound was performed. A TSH value of ≥4.5IU/ml was considered as underlying hypothyroidism.

Results: Among the entire cohort, 158 subjects became hypothyroid, while the remaining 530 remained euthyroid off LT4-Rx (23 vs. 77%, P<0.001). On subgroup analysis, 40% of subjects comprising Group A became hypothyroid, whereas the corresponding value for Group B was 3%. In Group A, the rationale for LT4Rx, LT4 dose, LT4 dose/BMI, TSH levels, and the existence of thyroid autoantibodies (ATA) were significantly different in those who became hypothyroid. No difference among any parameters evaluated was observed in Group B. Subjects with a diagnosis of Hashimoto’s thyroiditis, positive ATA, higher TSH values, and higher LT4 dose were significantly more likely to become hypothyroid. Furthermore, in Group A, 15.4% became hypothyroid with baseline TSH>3IU/ml vs. 5.4% with baseline TSH<3IU/ml (P<0.001); the corresponding values for Group B were 44.4% vs. 10.0%, (P<0.001), respectively.

Conclusions: These findings suggest considerable overuse of thyroxine administration. In cases of uncertainty, the existence of nodules, low-normal TSH level a relatively small T4 dose, and absence of ATA are strong indicators of euthyroid patients’ overuse of the LT4Rx and, accordingly, treatment discontinuation is strongly advised. Furthermore, in the case that a subject does not become hypothyroid 2-4 months post treatment discontinuation, the likelihood of developing hypothyroidism long-term is insignificant.

Reference1. Livadas S, et al. Thyroid 2018.