Thyroid Highlights From ENDO 2021

Angela M. Leung, MD, MSc


March 30, 2021

Editorial Collaboration

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This year's virtual Endocrine Society annual meeting was another excellent event packed with exciting content. Here are a few interesting highlights from the thyroid research presented.

Does Radioactive Iodine (RAI) Treatment for Hyperthyroidism Lead to Cancer?

One of the most well-attended sessions at this meeting was a balanced, spirited, and provocative debate on this topic between Cari Kitahara, PhD, from the National Cancer Institute (arguing the affirmative) and Brian Kim, MD, from Rush University Medical Center (arguing the negative).

Ionizing radiation is a known carcinogen that is associated with increased risks for both solid and hematologic cancers. Dr Kitahara summarized a recent study by her group that examined the largest cohort of patients with hyperthyroidism treated with RAI (18,805 participants followed for up to 70 years). This study reported increased risks for all solid cancers, specifically female breast cancer, even at relatively lower RAI doses than those traditionally used for thyroid cancer ablation.

From the opposing perspective, Dr Kim reassuringly reminded us that there are over 100 years of data on the risks associated with RAI use related to thyroid cancer, although the historical studies are widely heterogeneous. This evidence has resulted in several societal recommendations assuring the overall safety of RAI use in patients with hyperthyroidism.

Overall, the session was a great discussion on this important and thought-provoking topic. Perhaps the speakers phrased it best in their respective viewpoints: It's important to consider the differing quality of the historical studies, and the recent data should serve as a signal for additional studies employing more modern epidemiologic/statistical techniques.

And finally, some provocative questions: How do we define safety when speaking about RAI use? Is it the absolute absence of any and all adverse effects, or is safety defined by the outweighing of benefits over these exceedingly rare risks? This session showed that we need to find ways to better communicate the concept of RAI-related risks to patients in order to more effectively and accurately reflect the pros and cons of this common treatment.

One Third of Older Adults Take Medications That May Interfere With Thyroid Hormone Replacement

It is remarkable that levothyroxine has been the most widely prescribed medication in the United States for the past several years. For clinicians managing hypothyroidism, it is common to ask what other medications patients are taking. Our goal is to optimize the consistency of thyroid hormone absorption and ensure the accuracy of serum thyroid function tests.

Dr Rachel Beeson and colleagues from the University of Michigan reported that among 538,137 thyroid hormone users aged ≥ 65 years from the US Veterans Health Administration, nearly one third (31.6%) were concurrently taking at least one medication that could potentially be a thyroid interference. Examples included prednisone, prednisolone, carbamazepine, phenytoin, phenobarbital, amiodarone, lithium, interferon-alpha, and tamoxifen. Factors associated with taking one of these medications included non-White race, Hispanic ethnicity, female sex, and presence of comorbidities. In contrast, age ≥ 85 years was less likely to be associated with concurrent use of interfering medications.

This report is very clinically relevant to the practicing general endocrinologist as well as clinicians in primary care. It is notable that managing thyroid hormone replacement in older patients is complex. Many of our patients are at risk for adverse effects from thyroid hormone use and monitoring, particularly in the context of polypharmacy and multiple comorbidities.

An Effective Alternative Treatment for Differentiated Thyroid Cancer Recurrences

Drs Marlen Alejandra Alvarez Castillo and Antonio Segovia Palomo from the Hospital General de Mexico Dr Eduardo Liceaga presented a poster abstract regarding the use of percutaneous polidocanol injection (PPI) for a patient with a structural differentiated thyroid cancer recurrence.

Their case was a 35-year-old woman with a history of AJCC stage I papillary thyroid cancer who developed a 0.97-cm right level III lymph node recurrence at 8 months after total thyroidectomy and RAI ablation. The patient was treated with PPI, a therapy that is available in Latin America and may be a good option in regions where 99% ethanol, required for percutaneous ethanol injection (PEI), is not widely obtainable. At 1 month, PPI reduced the lesion size to 0.1 cm, and at 4 months, the mass completely disappeared; correspondingly, the thyroglobulin concentration from the washout decreased from 4743.72 ng/mL to 2.4 ng/mL.

PPI is an option for shrinking thyroid nodules/masses that is not as frequently used as other interventional thyroid techniques such as PEI and thermal ablation. The authors noted that the risk for hematoma with PPI is comparable to that of the more common practice of PEI, but PPI usually requires fewer sessions and tends to be less painful. PPI therapy has been used for hemangiomas, hemorrhoids, gastric varices, varicose veins, and hepatic and renal cysts.

Most of the available literature has described PPI as an option primarily for benign thyroid cysts rather than solid thyroid cancers. With this abstract, the authors nicely share their expertise from having treated nearly 50 patients with parathyroid adenomas, thyroid cysts, and thyroid cancer recurrences with PPI since 2017 at their institution.

Angela M. Leung, MD, MSc, is an endocrinologist at UCLA Health and the VA Greater Los Angeles Healthcare System and an associate professor of medicine in the Division of Endocrinology, Diabetes, and Metabolism at the UCLA David Geffen School of Medicine. She speaks on the topics of iodine nutrition, environmental thyroid toxicants, thyroid nodules, and thyroid cancer and serves on the Medscape Endocrinology advisory board.

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