Endocrine Abstracts

Case Presentation

A 25-year-old lady presented with symptomatic hyperthyroidism. She had a 4–6-week history of unexplained weight loss, pain in her neck and difficulty swallowing. Bloods confirmed mild hyperthyroidism with TSH 0.19 mU/l (reference range 0.27-4.2) with free T4 24.4 pmol/l (reference range 12.0-22.0), and she was commenced on carbimazole. There was no evidence of inflammation with CRP < 1 mg/l. Her mother had a thyroidectomy for thyroid cancer. Ultrasound of the thyroid showed multiple nodules with U2 features with no evidence of thyroiditis. She had positive TPO antibodies 415 IU/ml (reference range 0-5.5). Carbimazole was rapidly tapered to the lowest dose, and thyroid function stabilised. She has been under the sleep disorder clinic for severe sleepwalking and sleep-related eating disorder (SRED), which was treated with Topiramate with modest effect. Topiramate was considered a possible cause of thyroiditis, on a background of elevated TPO antibodies, and this medication was therefore discontinued.

Discussion

Topiramate was initially approved in 1995 in the UK as adjunctive treatment of partial-onset seizures. It blocks voltage-dependent sodium and calcium channels, inhibits the excitatory glutamate pathway while enhancing the inhibitory effect of GABA and inhibits carbonic anhydrase activity. In an open-label retrospective trial, Topiramate was found to be highly effective in reducing nocturnal eating in patients with chronic SRED. There have been no peer-reviewed studies of Topiramate induced hyperthyroidism; however, there are a few cases reports in the literature with no exact mechanism postulated. It is unclear whether Topiramate interacts with the immune system as postulated in non-thyroidal side effects. In our case, as the thyroid peroxidase antibodies were elevated this may have contributed to the possible effect of Topiramate on thyroid function.

Learning Points

Drug-related hyperthyroidism and thyroiditis need to be considered in biochemical thyrotoxicosis. Thorough drug history and clinical evaluation with correlating biochemistry are vital; however, there is often no definitive cause. In addition to the previous case reports of thyroid derangement observed with Topiramate, we also wanted to highlight our patient’s possible link. Further research is required into the exact mechanisms however thyroid autoimmunity may be an indicator of individuals who require thyroid function monitoring during treatment with Topiramate.

References

1. Pearce EN. Diagnosis and management of thyrotoxicosis. BMJ. 2006;332(7554):1369–1373. doi:10.1136/BMJ.332.7554.1369.