BACKGROUND
Hypothyroidism happens when our bodies cannot produce thyroid hormone. It was recognized as a disease of the thyroid and treated using animal thyroid glands (desiccated thyroid extract, DTE) as early as the 6th century. Synthetic thyroxine (T4) was developed in the 1930’s and became the standard of treatment in the 1970’s. By this time, more accurate laboratory assays had been developed for diagnosis and evaluation of treatment response; also, enzymes called deiodinases that can convert T4 into triiodothyronine (T3), the active thyroid hormone, inside the body were discovered. DTE was harder to dose accurately, because it came from animal thyroids which had more T3 than the human thyroid gland. As T3 is the more active thyroid hormone, excess T3 can cause problems with heart and bone health. Currently, levothyroxine (L-T4) is the recommended treatment for hypothyroidism worldwide. In recent years, more patients have been interested in using alternative treatments like DTE. Some prefer this option considering it to be a more natural treatment. Another reason is that despite normal thyrotropin (TSH) levels while on treatment with LT4, about 15% of patients do not feel well, which drives interest in other options.

The researchers wanted to learn more about the effectiveness and safety of DTE to guide doctors and patients. They designed this study to systematically review and summarize the available evidence on the potential risks and benefits of DTE compared to conventional therapies like L-T4.”

THE FULL ARTICLE TITLE
Riis K et al Potential risks and benefits of desiccated thyroid extract for the treatment of hypothyroidism: a systematic review. Thyroid 2024;34(6):687-701; doi: 10.1089/thy.2023.0649. PMID: 38526391.

SUMMARY OF THE STUDY
The authors reviewed existing research on adult patients 18 years and older who were treated for hypothyroidism using DTE. They searched electronic databases for studies published up to January 2024. They focused on studies that compared DTE with other thyroid treatments like L-T4 only, combination of L-T4 with T3 or in some cases no treatment. They did not include studies where TSH was not used to diagnose and monitor hypothyroidism. The primary outcome studied was quality of life (QoL). They also looked at whether DTE reduced hypothyroid symptoms, which treatment patients preferred, results of thyroid tests, genetic factors that can influence the effect of treatment, changes in body weight and cholesterol and potential side effects.

There were 9 nonrandomized studies (NRCTs), 2 randomized clinical trials (RCT’s), and 3 case reports in the final analysis. Overall, the quality of the studies ranged from moderate to low. NRCT’s do not assign patients randomly to treatment groups so results may be influenced by factors other than the studied treatment, such as patient selection and expectations of the patient or the researcher. RCT’s on the other hand are strictly controlled, for this type of study patients get randomly assigned to treatment groups and researchers and patients are kept unaware of the group assignments. This makes RCT results more reliable but less dramatic.

In the 2 RCT’s, there were no clear differences in QoL or symptom control. NRCT’s suggested that DTE may improve QoL and reduce symptoms for some patients. The effect of DTE on the TSH levels was inconsistent in all the studies. Some studies showed higher T3 levels on DTE, and all studies showed lower T4 levels on DTE compared to L-T4 treatment. There were no differences in body weight, blood pressure, or cholesterol levels.

WHAT ARE THE IMPLICATIONS OF THIS STUDY?
Overall, there was not enough evidence showing a benefit of using DTE compared to standard treatments. Even though some patients seemed to prefer DTE over L-T4, it didn’t consistently improve QoL or symptom scores. Perhaps the most important message to take away from this study is that there aren’t enough high-quality studies to make strong conclusions about DTE. In many studies, the treatment regimens were very variable, patients were not always comparable, tools that were used to measure outcomes were not consistent and follow up periods were short. We need studies with better design to understand how well DTE works and whether it’s safe. This study gives valuable information about how future studies in this area should be designed to find how DTE works for patients that don’t feel well after using L-T4, how genetics may affect conversion of T4 into T3 in the body, and how to give DTE to mimic how the thyroid naturally works. Patients interested in DTE should carefully discuss the benefits and risks with their doctor to decide on the best treatment option together.

— Ebru Sulanc, MD

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