Endocrine Abstracts

Background: Levothyroxine (LT4-Rx) is one of the most prescribed drugs worldwide and the vast majority of patients receive long-term treatment. However, in a recent study of 291 subjects we found that 60% of this cohort were euthyroid two 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, the treatment was abruptly interrupted. The treatment indications and corresponding percentage for LT4-Rx were classified as nodule(s) (33%), indefinite (27%), post-partum (7%) and Hashimoto’s (33%). Follow up for a short period of time occurred in 54% of subjects (≤ 4 months, Group A) and long-term follow-up was achieved in the remaining (up to 60 months, Group B). The studied subjects were evaluated at the time LT4-Rx 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 ≥4.5 IU/ml was considered as underlying hypothyroidism.

Results: Among the entire cohort, n=158 subjects became hypothyroid, while the remaining n=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 reason for LT4-Rx, 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 parameter evaluated was disclosed in Group B. Subjects with diagnosis of Hashimoto’s, positive ATA, higher TSH values and higher LT4 dose had significantly higher probability to became hypothyroid. Furthermore, in Group A, 15.4% became hypothyroid with baseline TSH>3 IU/ml vs. 5.4% with baseline TSH<3 IU/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, a low-normal TSH value, a relative small T4 dose and the absence of ATA are strong indicators of euthyroid patients on LT4Rx and accordingly treatment discontinuation is strongly advised. Furthermore, in the case that a subject does not became hypothyroid 2-4 months post treatment discontinuation, then the likelihood to develop hypothyroidism long term is insignificant.

Livadas S, et al. Thyroid 2018.