Objective: Most hypothyroid patients require an optimal dose of 1.61.8 μg/body weight (kg) of L-thyroxine to restore a normal TSH. Poor response to treatment can be due to malabsorption, drugs interaction and poor compliance. We conducted a test to determine the likely cause of persistent hypothyroidism in a coeliac patient despite taking supraphysiological doses of L-thyroxine (>1000 μg OD).
Case report: This is a 41 year old female who developed a post-RAI hypothyroidism, which was difficult to treat. Her TSH levels were persistently elevated (>30 mU/l) despite taking once daily dose of 10001400 μg L-thyroxine and admission of good compliance. Liothyronine was added on but gave little value. Her other significant medical problems include coeliac disease, diarrhoea-predominant irritable bowel syndrome, previous subarachnoid haemorrhage and asthma.
Method: Stage 1: Thyroxine absorption test: Baseline TSH and free T4 were checked (47.17 mU/l and 6.5 pmol/l). A 1000 μg L-thyroxine dose was administered. The fT4 levels were repeated, and they rose to 8.9 pmol/l (60 min), 14.1 (120 min), 14.4 (180 min) and 16.8 (240 min), which suggested a degree of absorption. Stage 2: Observed weekly thyroxine administration. Patient was given 1000 μg of L-thyroxine once/week for 4 weeks. A repeat TFT checked 4 weeks after this protocol demonstrated a huge improvement in her TFT, with TSH 1.65 mU/l and fT4 13 pmol/l. A repeat thyroxine absorption test at the end of this 4 weeks period confirmed a good degree of absorption.
Conclusion: A thyroxine absorption test followed by weekly thyroxine administration as described by Walker JN et al. (Eur J Endocrinol 2013; 168:9137) can determine the underlying cause of poor response to thyroxine treatment. As in this case, we suspected poor compliance and we modified the doses from 1400 μg L-thyroxine OD to 1000 μg twice weekly with good response. Future raise in TSH levels would prompt an observed L-thyroxine administration to improve compliance.