There exists an ongoing controversy about whether thyroid patients need both rapidly-acting T3 and long-acting T4 to treat hypothyroidism. The Endocrine Society’s recent meeting included an important clinical presentation entitled Controversies in Thyroid Hormone Replacement, which provided news about new research.
Dr. Hector F. Escobar-Moreale and colleagues from the Molecular Endocrinology Institute in Madrid, Spain, described research in which they gave thyroid hormone treatment to rats from which the thyroid had been removed and all remaining thyroid tissue had been destroyed with radioactive 131I.
After confirming hypothyroidism, osmotic minipumps were implanted under the skin for infusion with either T4 alone (in various concentrations), or several combinations of T4 plus T3. Rats with normal thyroid function served as controls. Infusion of T4 alone was unable to restore normal levels of T4 and T3 in plasma and in the thyroid tissues of the rats. Although both T4 and T3 appeared in tissues, the various levels were not the same as found in normal rats.
Dr. Escobar-Moreale emphasized that there was more work to be done to determine the importance of reaching the exact levels of T4 and T3 found in normal individuals. Rats, for example, normally have a 6:1 ratio of T4 to T3 in tissues. It is not clear how important an exact match of normal ratio is in either rats or patients to correct evidence of hypothyroidism and relieve symptoms.
Drs. Robertas Bunevicius and Arthur Prang, Jr., from the Institute of Endocrinology in Kaunas, Lithuania, and the Department of Psychiatry at the University of North Carolina, Chapel Hill, respectively, reported on an important follow-up study. They discussed additional evidence that treatment with T3/T4 combinations seems to improve mood in comparison with patients who are treated with T4 alone.
In 1999, the group described the results of treating 33 hypothyroid patients with T4 alone or with a reduced amount of T4 combined with a small amount of T3. Improvements in mood state, cognitive functioning, and concentration of sex hormone-binding globulin occurred after combined treatment. Later, they reported that improvements in psychological functioning seemed more evident in cancer patients than in patients with autoimmune thyroiditis. More recently, they studied ten patients with hypothyroidism following the removal of the thyroid gland for Graves’ disease. Here, too, the combination of T4 plus T3 seemed to improve mood in comparison to treatment with T4 alone.
Although these new figures support the original research hypothesis of Drs. Bunevicius and Prang, those in the audience seemed to agree that the numbers of patients studied is still too small to be sure that patients with combination therapy are indeed better off than those taking T4 alone. One concern is that T3 may cause brief periods of temporary hyperthyroidism daily, which could have dangerous effects on the heart, causing heart arrhythmias and possibly even myocardial infarction, especially in elderly individuals or those with heart disease.
There is continuing interest in manufacturing a slow-release T3 product which would not cause temporary hyperthyroidism, but in the meantime, we expect new research and larger clinical studies to either confirm or refute the opinion of Drs. Bunivicius and Prang.
More than three quarters of the people suffering from an underactive thyroid don't know it and have never been treated.