Changes in TSH levels in athyreotic patients with differentiated thyroid cancer during levothyroxine therapy: influence on dose adjustments

Abstract

Purpose: The aim of the study was to describe the spontaneous TSH level variations and levothyroxine dose adjustments in athyreotic patients with differentiated thyroid cancer (DTC) in real-life practice. Methods: Patients with DTC were retrospectively evaluated at a tertiary referral center between October 2006 and November 2013. Hormone measurements (TSH and FT4 serum levels), L-T4 prescription information (dose per kg per day) and other medications were recorded at 1 month and 3, 12, 24, 36 and 48 months after primary treatment (surgery ± radioiodine therapy). Results: The cohort was composed of 452 patients; about 20% of patients with stable levothyroxine dose have clinically meaningful spontaneous TSH variations (defined as ΔTSH > 2 mcUI/mL) at yearly follow-up visit. Furthermore, about 25% of athyreotic DTC patients with stable dose have a ΔTSH > 1.5 mcUI/mL and about 40% a ΔTSH > 1 mcUI/mL during each follow-up visit. We further investigated whether this TSH variation would lead to subsequent dose changes. About 19.9–37.7% of DTC patients on stable LT4 dose on the previous visit had their levothyroxine dose reduced, while 7.8–14.9% increased due to TSH variations. We further evaluated the decision to change the dose in relation with the age-specific TSH range. Up to 77.2% of patients had their dose adjusted due to TSH falling below the age-specific range. Conclusions: Spontaneous serum TSH variations determine levothyroxine replacement therapy in athyreotic patients with DTC, requiring multiple dose changes.