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

Abstract

Hypothyroidism by non-compliance with levothyroxine therapy (pseudomalabsorption) is rare. The diagnosis is considered in patients with persistent severe hypothyroidism despite large doses of levothyroxine treatment. Intestinal malabsorption, drug and dietary interference with levothyroxine absorption and nephrotic syndrome should be excluded. Diagnosis of pseudomalabsorption can be demonstrated by using “ an oral 1000 µg of levothyroxine test” showing a rapid decrease of TSH and increase of T4. 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, IM or single weekly oral dosing of levothyroxine.