Endocrine Abstracts

Introduction: Levothyroxine is the treatment of hypothyroidism, achieving normal thyroid stimulating hormone (TSH) levels. The optimal dose of Levothyroxine may be affected by several factors such as age, gender, body weight, patient’ compliance, some medical disorders and drugs intake. Persistent hypothyroidism secondary to non compliance is rare and represents a diagnostic challenge.

The aim of this study was to describe cases with refractory hypothyroidism due to pseudomalabsorption of Levothyroxine.

Observations: We report three patients who presented with persistent primary hypothyroidism despite high doses of Levothyroxine. All patients confirmed the good compliance with the hormone replacement therapy. An oral dose of 600 µg of Levothyroxine was administered under medical supervision. Baseline thyroid function tests were performed and repeated after 2, 4, 6 and 24 hours.

The first case was a 33-year-old man with a hypothyroidism diagnosed 19 years ago. He presented with a refractory hypothyroidism on 300 µg/d of Levothyroxine. The oral lévothyroxine test revealed a persistent high TSH level and low FT4 level consisting with the diagnosis of lévothyroxine malabsorption. The serology of celiac disease was negative. Gastroscopy revealed H. pylori gastritis. After treatment, the patient presented with a persisting refractory hypothyroidism with a TSH levels of 1068 mIU/l and a FT4 level of 0.46 ng/dl on 500 µg of Levothyroxine. The second patient was a 27-year-old woman who was treated with radioactive iodine for Graves’ disease. She was on lévothyroxine replacement therapy since 3 years. She presented with a TSH level superior to 100 mIU/l and a FT4 level of 0.51 ng/dl on 250 µg of Levothyroxine. The third patient was a 45-year-old woman who had a thyroidectomy and radioactive iodine for a thyroid papillary carcinoma 4 years ago. She had a TSH level of 26.144 and a FT4 level of 1.04 ng/dl on 400 µg of Levothyroxine. Oral lévothyroxine absorption challenge test revealed a correct increase in FT4 levels and a decrease in TSH levels in all patients. They were diagnosed with pseudomalabsorption, and were advised about compliance. The mean TSH after 3 months was 10.3 mUI/l under lower doses for two patients and same dose for the second one, secondary to a persistent non-compliance.

Conclusion: In the absence of evident causes of persistent hypothyroidism despite optimal doses of lévothyroxine, the oral absorption test under medical supervision is useful to diagnose pseudomalabsorption.