Marked Improvement of Levothyroxine Malabsorption by Simply Changing the Timing of Thyroxine Ingestion in an Adult Woman With Hypothyroidism After Radioiodine Therapy for Graves Disease

Abstract

We report the case of a 37-year-old woman suffering from hypothyroidism resistant to oral levothyroxine (LT4) substitution after radioiodine therapy for Graves disease. She was admitted to our endocrinology clinic for persistent hypothyroidism despite administration of full-dose LT4 (175 mg/day). The patient complained of severe general fatigue, leg edema, and body weight gain. Her serum free thyroxine (FT4) and thyrotropin (TSH) levels were 0.64 ng/dL and 58.0 mIU/L, respectively. Extensive investigations excluded disease of the small bowel, liver, and pancreas, as well as drug interactions. She also had no gastrointestinal diseases (for exmple, ulcer, inflammatory colitis). We were also able to rule out failure to take LT4 and concomitant use of other drugs. One month after changing the timing of LT4 ingestion from after breakfast to before breakfast, her serum TSH level did not decrease and her serum FT4 level increased from 0.64 to 1.02 ng/dL. The symptoms of hypothyroidism remained unchanged. We then changed the timing of LT4 ingestion from morning to bedtime. One month later, her serum TSH level had normalized and signs of hypothyroidism had disappeared. This case emphasizes the clinical importance of the timing of thyroxine ingestion in not a few patients with hypothyroidism resistant to LT4, although the reason for the malabsorption in this patient remains unclear.




J Endocrinol Metab. 2012;2(6):232-234
doi: https://doi.org/10.4021/jem129w