Thyroid hormone plays a vital role in regulating human metabolism. They affect the functions of major organs, such as the brain, liver, skeletal muscle, and heart. Hypothyroidism can lead to dilated cardiomyopathy and decreased heart function. In this report, we describe a case of a teenage boy who developed dilated cardiomyopathy due to hypothyroidism and was considered to undergo heart transplantation. Levothyroxine monotherapy was initiated but produced no improvement. Thereafter, a combination therapy of liothyronine and levothyroxine was administered, and heart function was gradually restored; he recovered completely after 6 months. Cardiac myocytes respond more specifically to liothyronine than to levothyroxine. Therefore, we suggest that liothyronine and levothyroxine combination therapy should be considered rather than levothyroxine monotherapy for hypothyroidism accompanied by heart disease.
Keywords: Dilated cardiomyopathy; Heart failure; Hypothyroidism; Levothyroxine; Thyroid hormone; Triiodothyronine.