The addition of T3 also makes treatment and monitoring more complex. Treatment with T4 provides steady levels of both T3 and T4 hormones. However, when synthetic T3 is given, it builds up and then dissipates quickly, according to Jonklaas, who added that if patients on combination therapy aren't carefully monitored, they can develop symptoms of thyroid overactivity, such as heart palpitations and trouble sleeping.
In an attempt to put this debate to rest, Jonklaas and her colleagues followed 50 people between the ages of 18 and 65 who needed to have their thyroid removed due to thyroid nodules, cancer or a goiter. None of the volunteers had symptoms of underactive (hypo) or overactive (hyper) thyroid glands at the start of the study.
All of the study participants were treated with T4 alone after surgery.
The researchers measured T4 and T3 levels both before and after surgery and essentially found no change.
"This is further evidence that combination therapy is unlikely to be of use to people who've had thyroid surgery," said Dr. David Cooper, director of the division of endocrinology at Sinai Hospital of Baltimore and director of Johns Hopkins University's thyroid clinic. He wrote an editorial that accompanied the study.
Cooper did point out that there were some people who had slightly lower levels of T3 after surgery and that these people may be the ones who are candidates for combination therapy.
Both Jonklaas and Cooper said the findings are likely applicable to people who have improperly functioning thyroid glands as well, particularly for people with overactive thyroids that either have their thyroids removed or destroyed with radioactive iodine.
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