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Carbamazepine drug effect simulating biochemical central hypothyroidism in a patient with Bardet-Biedl syndrome
  1. David Kishlyansky1 and
  2. Gregory Kline2
  1. 1Department of Internal Medicine, University of Calgary, Calgary, Alberta, Canada
  2. 2Division of Endocrinology, Department of Medicine, University of Calgary Cumming School of Medicine, Calgary, Alberta, Canada
  1. Correspondence to Dr Gregory Kline; Gregory.kline{at}ahs.ca

Abstract

Carbamazepine (CBZ) is a medication used commonly in epilepsy. Decreases in free T4 levels simulating central hypothyroidism have been reported, although the clinical significance is still unclear. We present a 24-year-old man with Bardet-Biedl syndrome (BBS) who was found to have isolated biochemical central hypothyroidism. BBS is a ciliopathy occasionally associated with anterior pituitary dysfunction. While taking CBZ for epilepsy, his TSH was 1.73 mIU/L (reference range: 0.20–4.00 mIU/L) with a low free T4 of 6.6 pmol/L (reference range: 10.0–26.0 pmol/L). Pituitary MRI was normal. Although treated with levothyroxine initially, his apparent biochemical central hypothyroidism was later recognised as secondary to CBZ drug effect. This was confirmed with a normal free T4 of 12.2 pmol/L while he was off CBZ and levothyroxine. Despite the association between CBZ and biochemical central hypothyroidism, nearly all patients remain clinically euthyroid. This effect is reversible and recognition could lead to reductions in unnecessary thyroid replacement therapy if CBZ is discontinued.

  • endocrine system
  • drugs: endocrine system
  • thyroid disease

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Footnotes

  • Contributors DK planned and wrote the manuscript. GK is the patient’s adult endocrinologist and contributed to the writing and editing of the manuscript.

  • Funding The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.

  • Competing interests None declared.

  • Provenance and peer review Not commissioned; externally peer-reviewed.