Endocrine Abstracts

A 42 year old female presented with classical symptoms of hypothyroidism. Thyroid function tests confirmed hypothyroidism: TSH >100 mu/L and free T4 7 pmol/L. Thyroid peroxidase antibodies were significantly elevated at >3340 iu/ml. She was started on thyroxine 150 mcg but 3 months later the TSH remained elevated at 45 mu/L. Further review indicated no significant symptomatic improvement and TSH remained high at 61 mu/L. Her thyroxine dose was increased to 200 mcg but despite this her TSH continued to be raised. Poor compliance was discussed and she was not on any medications that impair absorption. The possibility of a malabsorption state such as coeliac disease was considered. Anti-endomysial antibodies were negative but gastric parietal cell and intrinsic factor antibodies were strongly positive. Gastric biopsy showed antral inflammation confirming pernicious anaemia. Her thyroxine dose was increased and she initiated on B12 injections. Symptom improvement was dramatic on the high dose of thyroxine and thyroid function tests normalised. Pernicious Anaemia is associated with atrophic gastritis and is a rare cause of thyroxine malabsorption. It is recognised that there may be an increased need for thyroxine in patients with impaired gastric acid secretion such as H.pylori-related gastritis, atrophic gastritis and in those using high-dose proton pump inhibitors. The mechanism by which intestinal absorption of thyroxine may be impaired in hypochlorhydric patients remains unclear. The efficiency of intestinal T4 absorption may be altered by the ionization status of the T4 molecule. Oral T4 preparation is a hydrophilic sodium salt that may remain undissociated under hypochlorhydric gastric environment and thus less efficiently absorbed through the intestinal lipid bilayer. While atrophic gastritis is a rare disease, it should be considered as a cause of sub-optimal thyroxine replacement. The optimal daily dose of T4 may need to be increased to compensate in these patients.

Declaration of interest: There is no conflict of interest that could be perceived as prejudicing the impartiality of the research reported.

Funding: No specific grant from any funding agency in the public, commercial or not-for-profit sector.