This transcript has been edited for clarity.
In this podcast, I'm going to talk about the diagnosis and management of subclinical hyperthyroidism in primary care. Let's start with a typical case we all might see in primary care.
Valerie is a 71-year-old lady who attended my clinic with a history of nonspecific malaise. Past medical history was significant and included atrial fibrillation, ischemic heart disease, and osteoporosis. Current medications are apixaban 5 mg twice a day, atorvastatin 40 mg once a day, amlodipine 5 mg once a day, and risedronate 35 mg weekly.
Valerie's widowed, lives alone, and is functionally independent, so I checked some bloods. Full blood count, kidney function, HbA1c, and calcium were all normal. LDL cholesterol levels were 2.1 mmol/L. However, thyroid function tests were reported as a thyroid-stimulating hormone (TSH) of less than 0.01 (normal range, 0.2-4.5), free T4 levels of 14 (normal range, 9-21), and free T3 levels of 3.8 (normal range, 3-6.5).
Valerie appears to have subclinical hyperthyroidism with a TSH suppressed below the normal reference range but with normal free T3 and T4 levels.
What do we do next? Do we repeat thyroid function tests in 2-4 weeks or wait a bit longer and simply repeat them in 6-8 weeks? Do we refer to endocrinology? Do we do this routinely or do we need to do this urgently?
Subclinical hyperthyroidism affects 5% of people over 60 years of age. Importantly, over 50% of cases of isolated low TSH with normal free hormones will return to normal with no treatment.
Subclinical hyperthyroidism progresses to overt hyperthyroidism in a minority of individuals, with lower TSH levels associated with a higher chance of progression. Endogenous causes include Graves’ disease, toxic thyroid nodules, transient thyroiditis, and nonthyroidal illness, the preferred terminology for sick euthyroid syndrome.
It can also be caused by individuals taking excessive doses of levothyroxine. Other iatrogenic causes include steroids, amiodarone, dopamine agonists such as pramipexole and ropinirole, cancer immunotherapies, and antiretrovirals. Rarely, subclinical hyperthyroidism can be caused by pituitary disease.
The main concern with subclinical hyperthyroidism is an increased risk of atrial fibrillation and heart failure, particularly in older individuals, an increased risk of cardiovascular and all-cause mortality, and also an increased risk of decreased bone mineral density and increased bone fracture risk, again, particularly in postmenopausal women.
However, the effectiveness of treatment in preventing these conditions does remain unclear. That said, if risk factors for any of these conditions are present, it is recommended to discuss with endocrinology for consideration of treatment.
What should I do for Valerie? I should assess her for clinical features of hyperthyroidism, which are quite varied: quick-onset malaise, compression symptoms of shortness of breath or hoarseness caused by a toxic multinodular goiter, emotional lability, heat intolerance, and unintentional weight loss, to name a few.
I should also consider checking for thyroid receptor antibodies. If underlying causes have been excluded, we can simply repeat thyroid function tests in 6 months in most individuals or sooner in older people or individuals at risk of the comorbidities I mentioned earlier: atrial fibrillation, heart failure, cardiovascular disease, and osteoporosis.
If the subclinical hyperthyroidism persists, especially in the presence of any of these high-risk comorbidities or in the presence of symptoms of thyrotoxicosis, individuals should be discussed with endocrinology.
Of course, if individuals have a thyroid nodule or goiter present and malignancy is suspected — for example, a hard or irregular goiter in the presence of local lymphadenopathy — then referrals should be made via suspected cancer pathway.
Treatment is usually offered to those with a TSH persistently less than 0.1, if over the age of 65 years. Also, treatment tends to be offered to postmenopausal women, to those with risk factors for osteoporosis or cardiovascular disease, or those with overt symptoms of hyperthyroidism.
In Valerie's case, she was asymptomatic from a thyroid point of view, and her thyroid receptor antibodies were negative. However, because she has three high-risk comorbidities with regard to subclinical hyperthyroidism, I referred her to endocrinology routinely for consideration of treatment.
Finally, although this podcast covered subclinical hyperthyroidism, I have produced a Medscape UK primary care hack or clinical aide - memoire on managing subclinical hypothyroidism in primary care for all healthcare professionals, which can be found at medscape-uk.co/Hacks. I hope you find this resource helpful.
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Any views expressed above are the author's own and do not necessarily reflect the views of WebMD or Medscape.
Cite this: Subclinical Hyperthyroidism in Primary Care - Medscape - Jan 13, 2025.
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