# Successful Treatment of Bexarotene-Induced Central Hypothyroidism

## TL;DR

A patient with skin cancer developed thyroid issues from a drug called bexarotene and needed high doses of thyroid hormone supplements to manage it.

## Contribution

This case highlights the need for high-dose levothyroxine and liothyronine to treat bexarotene-induced central hypothyroidism.

## Key findings

- The patient required 2.8 times the weight-based levothyroxine dose plus liothyronine.
- Free T4 and total T3 levels were normalized with a combination of 600 mcg levothyroxine and 15 mcg liothyronine.
- Central hypothyroidism due to bexarotene may require higher thyroid hormone supplementation than standard dosing.

## Abstract

The synthetic retinoid bexarotene (BXT), used in the treatment of cutaneous T-cell lymphoma (CTCL), has been associated with central hypothyroidism due to suppression of thyrotropin (TSH) secretion and upregulation of peripheral thyroxine (T4) and triiodothyronine (T3) metabolism. We present a case of a 41-year-old man with CTCL who developed central hypothyroidism within 1 month of receiving BXT. He required sequential uptitration of levothyroxine (LT4) over 15 months, and free T4 (FT4) and total T3 levels were normalized by a daily regimen of LT4 600 mcg and liothyronine (LT3) 15 mcg. While almost all patients regain normal hypothalamic-pituitary-thyroid axis function after cessation of BXT, there are limited data regarding LT4 and LT3 dosing required to adequately treat central hypothyroidism in patients on BXT. Our patient required an LT4 dose approximately 2.8 times the calculated weight-based dose and LT3 supplementation, demonstrating a large LT4/LT3 combination dose may be required to compensate for BXT-induced central hypothyroidism.