What is hyperthyroidism? Definition and facts

Hyperthyroidism is a condition in which there is excessive production and secretion of thyroid hormones by an overactive thyroid. This leads to a hypermetabolic state of increased metabolism characterized by an abnormal increase in the body’s basal metabolic rate.

It is a condition, wherein the thyroid gland becomes overactive leading to excessive amounts of its hormones, triiodothyronine (T3) and thyroxine (T4) into the blood (thyrotoxicosis).

Thyrotoxicosis is a clinical state in which there is excess thyroid hormone activity, usually due to high-circulating thyroid hormones. The clinical picture varies, ranging from an asymptomatic status to a life-threatening thyroid storm.

This overactive thyroid can cause certain complications to develop, which can be serious.

What causes hyperthyroidism?

There are various causes that can give rise to hyperthyroidism. They can be intrinsic and extrinsic.

Diffuse toxic goiter (Graves’ disease), toxic multinodular goiter (Plummer disease), toxic adenoma, and subacute thyroiditis account for about 90% of all cases.

Graves’ diseases

Graves’ disease is named after Robert Graves, an Irish physician who discovered it about 150 years ago. It is also referred to as diffuse toxic goiter.

In this condition, the thyroid is enlarged and the entire gland produces excessive T3 and T4. It accounts for hyperthyroidism in 70% of people. It is 7 to 8 times more common in women than men and tends to run in families indicating a hereditary trait.

Graves’ disease is basically an autoimmune disorder in which certain antibodies in the blood attack the thyroid causing it to grow in size and produce excessive hormones.


Thyroiditis is a painful inflammation of the thyroid accompanied by a fever. It may cause hyperthyroidism and this subsides once the inflammation is brought under control. Little is known about its etiology and why it occurs.

5% of women experience symptoms of thyroiditis after they have delivered a baby. However, this is painless and subsides after a few months.

Thyroid nodules

One or more nodules can develop in the thyroid and may cause hyperthyroidism. Here, only the thyroid cells in the nodules become hyperactive.

If excessive hormone production is being secreted from a single nodule in the gland, it is called toxic adenoma.

Hypothyroid medication

Excessive intake of thyroid medicines prescribed for hypothyroidism can cause hyperthyroidism. This is called factitious hyperthyroidism.

When this occurs due to a high prescribed dose, it is called iatrogenic, or doctor-induced hyperthyroidism. This is common and usually happens due to improper medical follow-ups.

Pituitary induced hyperthyroidism

In this condition, due to a tumor in the pituitary gland, there is excessive secretion of the Thyroid Stimulating Hormone (TSH) by the pituitary gland and this, in turn, triggers the excessive secretion of thyroid hormones.

You should know that the pituitary gland in the brain regulates the function of the thyroid gland through controlled TSH secretion.

Hyperthyroidism symptoms

Hyperthyroidism symptoms are not typical and may not immediately lead the physician to a diagnosis. Symptoms vary from individual to individual and in senior people, it can be mistaken as signs of aging.

The thyroid controls the metabolism in the body through the secretion of its hormones T3 and T4. Excessive secretion of these hormones leads to a hypermetabolic state and can give rise to corresponding symptoms.

  • Excessive sweating leading to a moist skin
  • Loss of hair
  • Cannot tolerate heat
  • Increased bowel movement
  • Anxiety
  • Fine tremors in hands
  • Improper Sleep
  • Breathlessness
  • Scanty menstrual flow
  • Fatigue and inability to concentrate
  • Increased heart rate causing palpitations
  • Loss of weight
  • Typical Staring gaze: This is called exophthalmos.

Effects of hyperthyroidism

  • Hyperthyroidism can lead to impaired tolerance to glucose causing a prediabetes condition.
  • Diabetes type 2 can also develop.
  • Tachycardia and atrial fibrillation are other complications, which can lead to congestive cardiac failure.
  • Osteoporosis may develop because increased levels of T3 and T4 interfere with the utilization of calcium by the bones.
  • Blurring and/or double vision may develop and the eyes become red and swollen.
  • Hoarseness of voice is another complication
  • A thyrotoxic crisis or storm may develop when a large amount of thyroid hormones are released. There is a sudden exacerbation of symptoms of hyperthyroidism. Delirium develops.

Diagnosis of hyperthyroidism

A detailed personal and family history and physical examination can give the physician a clue as to the nature of this disease and its cause.

For example, a family history or past history of autoimmune disease (rheumatoid arthritis, vitiligo, pernicious anemia) will raise suspicion of Graves’ disease.

Again, the presence of thyroid eye disease including periorbital edema, diplopia, or proptosis can be another pointer to Graves’ disease.

Patients with nontoxic goiter can develop toxic multinodular goiters.

Tests to diagnose hyperthyroidism

  • In hyperthyroidism, T3 and T4 levels in the blood rise above the normal range.
  • TSH levels fall below the normal range.
  • An iodine thyroid scan will indicate how much iodine uptake is there by the thyroid and help in diagnosis because iodine is used by the thyroid to make its hormones. In hyperthyroidism, iodine uptake is increased.
  • A lipid profile test will show reduced levels of serum cholesterol and triglycerides because of the increased metabolic rate in which the body burns these lipids very fast.
  • A thyroid scan will show if the whole thyroid gland is enlarged or only a particular part of it is causing hyperactivity.
  • The ultrasound of the thyroid will help measure the size of the thyroid and detect any mass and its consistency.
  • CT scan and MRI of the brain will help to rule out any pituitary abnormality.

Treatments for hyperthyroidism

There are three options involved in treating hyperthyroidism.


  • Methimazole(Tapezole) or Propylthiouracil(PTU). Anyone of these drugs may be used. They block the action of the thyroid hormones in the blood and interfere with the uptake of iodine by the thyroid gland, thereby blocking the formation of T3 and T4 by the thyroid gland.
  • Beta-blockers may also be given to block the side effects of hyperthyroidism on the heart.

Radioactive iodine therapy

Radioactive iodine therapy involves giving the patient radioactive iodine-131 to drink in appropriate doses. This radioactive iodine is different from the regular iodine present in our blood.

The iodine is taken up by the cells of the overactive thyroid and it gradually destroys the thyroid cells. As a result, the increased size of the thyroid is reduced and the thyroid hormone levels are brought to normal.

The radioactivity, however, goes away over a period of time. Chances of recurrence are there after a few months or years.

Surgery for hyperthyroidism

Surgery for hyperthyroidism is indicated when the above-mentioned conservative treatments fail or cannot be given to a particular patient due to some reason. Surgical removal of a nodule or the full thyroid gland is carried out as indicated. If possible, a small portion of the thyroid may be left to maintain the level of the thyroid hormones in the blood.

If total removal is required, then the patient has to be kept on thyroid replacement therapy throughout life.


The outlook and long-term outcome of a case of hyperthyroidism depend on what has caused it. In some cases, hyperthyroidism may resolve on its own, while other cases require treatment.

Thyroid disorders are generally referred to an endocrinologist for treatment and cure because any comorbidities can cause dangerous complications.

For example, improper treatment can precipitate a thyroid storm or thyrotoxicosis

Nodular goiters, whether multiple or single usually continue to grow in size gradually during treatment. Hyperthyroidism is permanent in such cases. Once the medication has normalized the thyroid function, radioactive iodine ablation is recommended.

If hypothyroidism sets in due to radioactive therapy, T4 is recommended once daily.

Graves’ disease can worsen over time if left untreated and its complications can be life-threatening. Early detection and treatment improve the long-term outlook.

Subclinical hyperthyroidism may resolve on its own or progress to clinical hyperthyroidism or it may remain in the subclinical state.