What is subclinical hyperthyroidism?

The subclinical hyperthyroidism (HSc or HiperSc), is a condition characterized by a low concentration of thyrotropin, the thyroid gland stimulating hormone (TSH). Those who have received this diagnosis do not present clinical symptoms and, in their blood tests, they show normal concentrations of thyroid hormones (free T3 and T4, according to the reference range of the laboratory). It is a disorder that must be treated to avoid negative health consequences. Indeed, if it becomes clinical hyperthyroidism (definitive and overt), it can become a risk factor for the development of osteoporosis and bone fractures of any kind: hip, spine, etc.

Below you will find a summary of the most important things you should know about this disorder: What is it? What are its most relevant causes, symptoms and consequences. You will also have information on hand about how it is diagnosed and what treatment is currently used to overcome it.

What are the causes of subclinical hyperthyroidism (HSc)?

The causes that generate subclinical hyperthyroidism are the same as clinical hyperthyroidism. They are usually grouped into two types:

Exogenous causes

  • In case the patient is under treatment for goiter, when the hormone levothyroxine sodium (L-T4) is administered excessively.
  • By suppressing the hormone thyrotropin (TSH) in people who have undergone surgery for thyroid cancer.
  • For doses higher than those necessary of the hormone levothyroxine sodium (L-T4), in the case of patients under treatment for hypothyroidism.
  • By consumption of certain drugs. Among these is amiodarone, which is frequently used to treat arrhythmias, but is high in iodine. One amiodarone tablet will provide 20 to 40 times more iodine than necessary. Hence the high probability of generating the disorder.

Endogenous causes

When suffering from Graves’ disease. This etiology (or cause of the disease) is more common in young patients. If you suffer from toxic multinodular goiter. This case is more common in adults over 65 years of age.

What symptoms do patients diagnosed with HSc present?

The main symptoms that patients with a diagnosis of subclinical hyperthyroidism may show are the following:

  • Palpitations
  • Heat intolerance
  • Sweating
  • Excessive nervousness
  • Trembling in the hands
  • Fatigue
  • Insomnia
  • Weightloss
  • Increased appetite
  • Diarrhea
  • Menstrual disturbances
  • If there are enlarged eyes, it could be Graves’ disease

Consequences of exogenous and endogenous HSc

Whatever the cause of subclinical hyperthyroidism, this condition can cause the following consequences:

  • Cardiovascular effects in those who suffer from it. There may be increased heart rate, arrhythmias, and tachycardia. It increases the risk of morbidity and mortality as it helps to develop cardiovascular diseases. In young people, cardiovascular risk increases when they suffer from Graves’ disease. Cardiovascular effects are more common in older adults.
  • There is an increased risk of suffering from atherosclerotic disease. Reports show a tendency to develop thrombosis and an increase in the inner layer of the carotid artery, that is, the main artery that carries blood from the heart to the head.
  • Transformation into clinical hyperthyroidism. Already in this case, the risk of suffering osteoporosis and fractures increases. The risk is higher in postmenopausal women, especially when the causes of hyperthyroidism are endogenous. In men, these risks become apparent after the age of 65, approximately.

How is the diagnosis of this disorder made?

This diagnosis is made by biochemical means. The reference values ​​for thyrotropin hormone (TSH) are between 0.45-4.5µU / mL.

Two types of subclinical hyperthyroidism can be distinguished:

  • Of slight alteration of TSH. The range of this diagnosis is between 0.45 and 0.1 µU / mL.
  • Of severe alteration of TSH. Here the diagnostic range is TSH ˂0.1 µU / mL.

Patients with TSH values ​​below the reference range may continue to be symptom free for months or years. Those who suffer from subclinical hyperthyroidism of endogenous etiology, usually respond to treatment and overcome this condition. In addition, the cases of HSc that each year transform into definitive clinical hyperthyroidism are reduced.

It is recommended to repeat the TSH measurement 1 to 3 months after you obtain a TSH value of ˂0.45 µU / mL. The specialist will consider whether it is necessary to complete the evaluation by ordering other tests.

It must be taken into account that some medications such as dopamine and corticosteroids tend to reduce TSH levels, which can lead to suspect that the patient suffers from some form of hyperthyroidism. That is why it is so important that you inform your doctor of other drugs you are taking.

During diagnosis it is also necessary to consider that another possible cause of subclinical hyperthyroidism may be: pregnancy during the first three months and, in this case, it tends to be transitory. It usually resolves spontaneously and symptomatic treatment is indicated, if required.

The cases of multinodular goiter should be attended especially, because they can develop definitive clinical hyperthyroidism if they receive excess iodine during their treatment (iatrogenism).

What treatment is recommended to overcome it?

Treatment depends on the cause of the subclinical hyperthyroidism and the condition of the patient. Spontaneous remissions are common with this disorder. Therefore, it is best to monitor the patient and follow up.

A multidisciplinary team must attend to the case, depending on the diagnosis. This must be constituted, at first, by the endocrinologist. If any complication occurs, it should also be treated by another specialist, depending on the case.

  • Those patients with a large goiter will likely be referred for surgery.
  • If a lowered TSH is confirmed, the drug should be discontinued (to rule out that it is caused by the prescribed drug) or replaced.
  • In cases of arrhythmias or weight loss for no apparent reason, antithyroid drugs will likely be prescribed.
  • Patients who are indicated for treatment with iodine 131 will need the care of a nuclear medicine specialist.
  • Those receiving levothyroxine sodium replacement therapy should have their TSH levels checked to see that they are within the normal reference range of serum laboratory tests.

Subclinical hyperthyroidism is a common medical problem that can usually resolve on its own. In case treatment is required, it depends on the causes that originate it. Hence the importance of a timely and accurate diagnosis.

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