Pseudo malabsorption of levothyroxine
M. Alves, D. Rodrigues, C. Baptista, C. Ribeiro, P. Oliveira, A. Vieira, S. Gouveia, J. Saraiva, C. Moreno, M. Bastos & M. Carvalheiro
Background: Therapy with levothyroxine (L-T4) is essential in hypothyroidism treatment. The marked elevation of thyrotropin (TSH) in patients treated with appropriate doses of L-T4 is rare and can result from malabsorption, drug interaction or poor adherence. The non-adherence, omitted by the patient, is called pseudo malabsorption.
Clinical report: ACCS, female, 30 years old, hospitalized for persistent hypothyroidism despite L-T4 therapy. Personal history: submitted to total thyroidectomy in March 2010 because cytological suspicion of follicular tumor in a simple multinodular goiter. The histology revealed a papillary microcarcinoma (T1N0M0), without other changes. Started replacement therapy with L-T4. After increasing doses of L-T4 (125 to 400 μg/day) there was no normalization of TSH or thyroid hormones (TSH 74.3→93→50 μUI/ml (RR: 0.44.0), FT4 0.2→0.4→0.5 ng/dl (RR: 0.81.9)), with reappearance of thyroid tissue in surgical loca. Admitted to hospital for surveillance of taking L-T4 and study of possible L-T4 malabsorption.No drug habits. Physical examination: BMI 29 kg/m2, without major clinical signs of thyroid dysfunction. Laboratory: TSH 74 μUI/ml, FT4 0.4 ng/dl. Blood count, biochemistry, folic acid, vitamin B12, iron metabolism, stool examination, research and degree of fat digestion of feces, autoimmunity for celiac disease or pernicious anemia: all normal. Esophagus and gastric endoscopy was macroscopically normal; a gastric biopsy was performed and showed chronic antral gastritis, non-atrophic, with mild activity and colonization by H. pylori. The test of oral overload with 1 mg of L-T4 revealed: TSH 60 μUI/ml at baseline→33 μUI/ml after 4 h, FT4 0.7 ng/dl at baseline → 1.0 ng/dl after 4 h. This result confirmed the diagnosis of pseudo malabsorption of L-T4. The therapeutic regimens included confronting the patient with the results and the eradication of H. pylori.
Conclusions: The poor adherence to therapy is the most common cause of persistent hypothyroidism in patients receiving adequate doses of levothyroxine. Clinical suspicion should be investigated excluding malabsorption syndromes or drug interaction. In this patient, the high dose overload of levothyroxine allowed the confirmation of the diagnosis. Psychological counseling may be necessary.
Declaration of interest: The authors declare that there is no conflict of interest that could be perceived as prejudicing the impartiality of the research project.
Funding: This research did not receive any specific grant from any funding agency in the public, commercial or not-for-profit sector.