Pseudomalabsorption of Levothyroxine: A Challenge for the Endocrinologist in the Treatment of Hypothyroidism

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Background: Hypothyroidism due to non-compliance with levothyroxine therapy (pseudomalabsorption) is rare. The diagnosis is considered in patients with persistent severe hypothyroidism despite treatment with large doses of levothyroxine. Intestinal malabsorption, drug and dietary interference with levothyroxine absorption and nephrotic syndrome should be excluded. The diagnosis of pseudomalabsorption can be demonstrated by using “an oral 1,000 µg of levothyroxine test” showing a rapid decrease in thyroid-stimulating hormone and increase in thyroxine. There are however few data on the sensitivity and specificity of the test in large cohorts of hypothyroid patients. Treatment of pseudomalabsorption is controversial, with reports using parenteral, intramuscular or single weekly oral dosing of levothyroxine. Cases: We report 3 patients who presented with persistent clinical and biochemical signs of hypothyroidism despite replacement therapy with high doses of levothyroxine. Pseudomalabsorption was diagnosed by a systematic approach, including prior exclusion of digestive, liver and kidney diseases. A peroral challenge test was positive in all cases. Patients denied non-compliance, and a psychiatric approach was elusive. Two of the patients were treated successfully with a single supervised weekly 1,000-µg administration of levothyroxine, while non-supervised weekly administration resulted in hypothyroidism confirming pseudomalabsorption. Conclusions: Non-compliance with medical therapy should be considered in patients with treatment-refractory hypothyroidism. Supervised once weekly levothyroxine treatment is a safe and well-tolerated treatment option, obviating the need for parenteral administration of the drug. Apart from the medical treatment, there is also a need for psychiatric evaluation and care.

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