LBSAT247 Factors Guiding Successful Treatment Discontinuation In Levothyroxine Replacement Therapy Overuse: Short And Long-term Observation Data Of 802 Subjects.

BACKGROUND: Levothyroxine (LT4-Rx) is one of the most commonly prescribed drugs worldwide and the vast majority of patients receive long-term treatment. However, in a recent study of LT4-Rx withdrawal in 291 subjects, it was found that 60% of those remained biochemically euthyroid two months after LT4-Rx discontinuation1. AIM OF THE STUDY: A prospective clinical cohort follow-up study was carried out to address this issue. We registered all patients presented in our clinical practice who were not on LT4-Rx for a solid diagnosis of hypothyroidism and abruptly discontinued treatment. All subjects underwent weight, height, TSH, TPO, Tg-Abs and free T4 measurement and thyroid ultrasound on enrolment, 2-4 months later, and at the end of follow up. A TSH value of ≥4.5IU/mL was considered as underlying hypothyroidism. RESULTS: We enrolled 802 consecutive subjects (83% females) aged 48±16 (range 18-84 years) with 8.8±7.3 years on LT4-Rx. The treatment indications and corresponding percentage for LT4-Rx were classified as a nodule(s) (35%), indefinite (25%), post-partum (7%) and Hashimoto's (33%); 48% of subjects were part of Group A and long-term follow-up up to 5 years was achieved in the remaining. Among the entire cohort, n=182 subjects became hypothyroid, while the remaining n=620 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 7%. In Group A, the reason for LT4-Rx, LT4 dose, LT4 dose/BMI, TSH levels and the presence of increased thyroid autoantibodies titers (ATA) were significantly different in those who became hypothyroid, whereas only the reason for LT4-Rx differed in Group B. Subjects with a diagnosis of nodules, negative ATA, lower TSH values and lower LT4 dose during treatment had significantly lower probability to become hypothyroid. Furthermore, in Group A, 14.8% became hypothyroid with baseline TSH>3IU/mL vs. 5.2% with baseline TSH<3IU/mL (p<0. 001); the corresponding values for Group B were 22.2% vs. 8.8%, (p<0. 001), respectively. CONCLUSIONS: These findings suggest considerable overuse of thyroxine therapy. In cases of uncertainty, the existence of nodules, a low-normal TSH value, a relatively small T4 dose, and the absence of ATA are strong predictors of euthyroidism, and accordingly a treatment discontinuation trial is recommended. Furthermore, if hypothyroidism does not ensue 2-4 months post-treatment discontinuation, the likelihood to develop hypothyroidism in the long term is minimal.1. Livadas S, et al. Thyroid 2018. Presentation: Saturday, June 11, 2022 1:00 p.m. - 3:00 p.m.