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 A recent case study provides a snapshot of the larger problem, the
authors write in JAMA Internal Medicine.
Just 1 percent to 2 percent of people have hypothyroidism, in which
their thyroid gland is underactive and requires treatment, coauthor
Dr. Juan P. Brito of the Mayo Clinic in Rochester, Minnesota, told
Reuters Health. But about 15 percent of people have “subclinical
hypothyroidism” - hormone levels that are between the healthy range
and the diagnostic cutoff for hypothyroidism and that cause few or
no symptoms.
Clinical hypothyroidism can cause constipation, depression, fatigue,
dry skin, unexplained weight gain and greater sensitivity to cold.
The authors present the story of a 72-year-old obese man with type 2
diabetes, high blood pressure and heart disease who complained to
his doctor of fatigue. The doctor ordered a hormone panel and found
a blood thyroid-stimulating hormone (TSH) level of 7.2 microunits
per milliliter (mlU/L).
TSH triggers the thyroid to make hormones that control metabolism,
so elevated TSH is considered a sign the thyroid might be making too
little thyroid hormone. The healthy TSH reference range for adults
is usually 0.3 to 5.0 microunits per milliliter.
The elderly patient was prescribed 75 micrograms daily of
levothyroxine, available under brand names like Synthroid and
Novothyrox, to treat subclinical hypothyroidism.
A month after starting the medication, the patient came to the
emergency room with heart palpitations, labored breathing and chest
pain. A new hormone panel found his TSH levels had dropped to 0.1
mlU/L.
Doctors brought his heart rate under control and stopped
levothyroxine therapy. Three months later his heart rhythm had
returned to normal and his TSH level was 5.6 mlU/mL. That was still
slightly above healthy reference range, but considering the pros and
cons of treating subclinical hypothyroidism, he and his clinicians
decided not to restart levothyroxine,
“There is some evidence linking subclinical hypothyroidism to
cardiovascular events,” Brito told Reuters Health. “But there’s no
really good argument or data to support treatment.”
Despite that, levothyroxine is the most prescribed drug in the U.S.,
he said. A 30-day supply of generic levothyroxine costs about $13,
according to Healthcare Bluebook.
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“This is what happens when we pay too much attention to values and
not to the patient,” Brito said.
The medication is relatively safe but may push TSH levels so low
that it causes side effects, like the ones this elderly patient
experienced, he said. Not all subclinical hypothyroidism may require
drug treatment, especially for the elderly.
“I don’t think it’s the spirit of the guideline to treat everyone,”
Brito said.
For the elderly, the healthy reference range may be higher than the
adult range – having a TSH of 5.6 mlU/L may still be healthy, he
said.
Healthy ranges may also differ by individual, said Dr. Jennifer
Mammen of Johns Hopkins School of Medicine, who was not involved in
the case study.
Testing TSH levels more than once in a three to six-month period may
also give a clearer picture of whether the thyroid is truly
underactive.
“Our recommendation for diagnosis of subclinical hypothyroidism is
to check the levels twice with a separation between them,” Mammen
told Reuters Health by phone.
“The vast majority of people with symptoms (like fatigue) do not
have thyroid problems to begin with,” she said.
SOURCE: http://bit.ly/2cWFJ8X JAMA Internal Medicine, online October
3, 2016.
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