BACKGROUND
Hypothyroidism is common, affecting 2-3% of the US population. When you include mild forms (subclinical hypothyroidism), up to 25% of certain populations may be affected. Thyroxine (T4) is the main thyroid hormone secreted by the thyroid gland. It is converted to triiodothyronine (T3) in other areas of the body where thyroid hormone acts. The thyroid also secretes T3 at a low level. Most of the actions of thyroid hormone are attributed to T3.
Levothyroxine (L-T4), the pill form of T4, is the most commonly recommended treatment for hypothyroidism. Long-term experience with this therapy suggests that it is safe and effective and is accepted by most patients with hypothyroidism, resolving most, if not all, of their hypothyroid symptoms. However, despite returning the thyroid hormone levels to normal, a certain percentage of hypothyroid patients continue to have symptoms attributed to hypothyroidism. This has led to a desire by patients to find alternative treatments to L-T4 alone. One such treatment is the use of combination therapy, adding L-T3 (liothyronine) with L-T4 to increase blood T3 levels. As a consequence, combination therapy with L-T4/L-T3 began to be used, despite the lack of evidence suggesting a real benefit. Interesting new data have emerged to suggest a genetic basis why some patients may do better on combination therapy. Rarely, changes in the enzyme that converts T4 to T3 (type 2 deiodinase) causes it to not work well. In these patients, more of their blood T3 levels may come from the thyroid rather than from the conversion of T4. Thus, in those patients, L-T4/L-T3 combination therapy may be preferred.
To help address this, the American Thyroid Association (ATA), the British Thyroid Association (BTA), and the European Thyroid Association (ETA) developed a consensus statement in which they reviewed the latest evidence of hypothyroidism treatment with L-T4/L-T3 and developed recommendations for future clinical trials.
THE FULL ARTICLE TITLE
Jonklaas J et al 2020 Evidence based use of LT4/LT3 combinations in treating hypothyroidism: A consensus document. Thyroid. Epub 2020 Dec 4. PMID: 33276704.
SUMMARY OF THE STUDY
To draft this consensus statement, a task force consisting of 12 experts in all aspects of LT4/LT3 combination therapy was formed. Comments from members of all three societies, as well as input from two patients involved in the conference, were also taken into account. A total of 34 consensus items were available for voting, of which 28 received at least a 75% approval and 13 full approval. The following are selected highlights from the published statement: