The Causes, Diagnosis & Treatment Of An Underactive Thyroid Gland

Born in NYC, and raised in NJ, Dr. Sandhu has traveled around the country for undergraduate school, medical school, and residency. He completed his Internal Medicine residency at Indiana University and then joined a large multi-care specialty group where he rapidly experienced many cases in a short amount of time. Now with roughly 10 years of medical experience, he is able to treat conditions ranging from congestive heart failure, COVID-19, diabetes, anxiety, bronchitis, sinusitis, and the common cold. 

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What does it mean when your body has an underactive thyroid? Here Haute MD expert Dr. Vineet Sandhu dives into the details of causes, diagnosis, and treatment regarding the most common thyroid disorder, hypothyroidism.

Most common causes

There can be many reasons why the cells in the thyroid gland can’t make enough thyroid hormone. Here are the major causes, from the most to the least common.

  • Autoimmune disease. In some people’s bodies, the immune system that protects the body from invading infections can mistake thyroid gland cells and their enzymes for invaders and can attack them. Then there aren’t enough thyroid cells and enzymes left to make enough thyroid hormone. This is more common in women than men. Autoimmune thyroiditis can begin suddenly or it can develop slowly over the years. The most common forms are Hashimoto's thyroiditis and atrophic thyroiditis.
  • Surgical removal of part or all of the thyroid gland. Some people with thyroid nodules, thyroid cancer, or Graves’ disease need to have part or all of their thyroid removed. If the whole thyroid is removed, people will definitely become hypothyroid. If part of the gland is left, it may be able to make enough thyroid hormone to keep blood levels normal.
  • Radiation treatment. Some people with Graves’ disease, nodular goiter, or thyroid cancer are treated with radioactive iodine (I-131) for the purpose of destroying their thyroid gland. Patients with Hodgkin’s disease, lymphoma, or cancers of the head or neck are treated with radiation. All these patients can lose part or all of their thyroid function.
  • Congenital hypothyroidism (hypothyroidism that a baby is born with). A few babies are born without a thyroid or with only a partly formed one. A few have part or all of their thyroid in the wrong place (ectopic thyroid). In some babies, the thyroid cells or their enzymes don’t work right.
  • Thyroiditis. Thyroiditis is an inflammation of the thyroid gland, usually caused by an autoimmune attack or by a viral infection. Thyroiditis can make the thyroid dump its whole supply of stored thyroid hormone into the blood at once, causing brief hyperthyroidism (too much thyroid activity); then the thyroid becomes underactive.
  • Medicines. Medicines such as amiodarone, lithium, interferon-alpha, and interleukin-2 can prevent the thyroid gland from being able to make hormones normally. These drugs are most likely to trigger hypothyroidism in patients who have a genetic tendency to autoimmune thyroid disease.
  • Too much or too little iodine. The thyroid gland must have iodine to make thyroid hormone. Iodine comes into the body in food and travels through the blood to the thyroid. Keeping thyroid hormone production in balance requires the right amount of iodine. Taking in too much iodine can cause or worsen hypothyroidism.

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Ways to diagnosis

  • Symptoms. Hypothyroidism doesn’t have any characteristic symptoms. There aren't common symptoms that people experience with hypothyroidism. In fact, many symptoms of hypothyroidism can occur in people with other diseases. One way to help figure out whether your symptoms are due to hypothyroidism is to think about whether you’ve always had the symptom (hypothyroidism is less likely) or whether the symptom is a change from the way you used to feel (hypothyroidism is more likely).
  • Medical and family history. You should tell your doctor:
    • About changes in your health that suggest that your body is slowing down;
    • If you’ve ever had thyroid surgery;
    • If you’ve ever had radiation to your neck to treat cancer;
    • If you’re taking any of the medicines that can cause hypothyroidism— amiodarone, lithium, interferon-alpha, interleukin-2, and maybe thalidomide;
    • Whether any of your family members have thyroid disease.
  • Physical exam. The doctor will check your thyroid gland and look for changes such as dry skin, swelling, and heart rate.
  • Blood tests.
  • TSH (thyroid-stimulating hormone) test. This is the most sensitive test for hypothyroidism. It measures how much of the thyroid hormone thyroxine (T4) the thyroid gland is being asked to make. An abnormally high TSH means hypothyroidism: the thyroid gland is being asked to make more T4 because there isn’t enough T4 in the blood.
  • T4 tests. Most of the T4 in the blood is attached to a protein called thyroxine-binding globulin. The “bound” T4 can’t get into body cells. Only about 1%–2% of T4 in the blood is unattached (“free”) and can get into cells. The free T4 and the free T4 index are both simple blood tests that measure how much unattached T4 is in the blood and available to get into cells.

Treatment option

Thyroxine (T4) Replacement. Hypothyroidism can’t be cured. But in almost every patient, hypothyroidism can be completely controlled. It is treated by replacing the amount of hormone that your own thyroid can no longer make, to bring your T4 and TSH levels back to normal levels. So even if your thyroid gland can’t work right, T4 replacement can restore your body’s thyroid hormone levels and your body's function. Synthetic thyroxine pills contain hormones exactly like the T4 that the thyroid gland itself makes. All hypothyroid patients except those with severe myxedema (life-threatening hypothyroidism) can be treated as outpatients, not having to be admitted to the hospital. For the few patients who do not feel completely normal taking a synthetic preparation of T4 alone, the addition of T3 (Cytomel®) may be of benefit.

The only dangers of thyroxine are caused by taking too little or too much. If you take too little, your hypothyroidism will continue. If you take too much, you’ll develop the symptoms of hyperthyroidism—an overactive thyroid gland. The most common symptoms of too much thyroid hormone are fatigue but the inability to sleep, greater appetite, nervousness, shakiness, feeling hot when other people are cold, trouble exercising because of weak muscles, shortness of breath, and a racing, skipping heart. Patients who have hyperthyroid symptoms at any time during thyroxine replacement therapy should have their TSH tested. If it is low, indicating too much thyroid hormone, their dose needs to be lowered.

For more information, visit Dr. Vineet Sandhu's social media: