Hypothyroidism – Diagnosis, Symptoms, and Treatment

Doctor Nathan LeDeaux, MD

Medically reviewed by Dr. Nathan LeDeaux, MD

Medical Professional

Updated - January 4, 2021

Nathan LeDeaux is an emergency medicine physician at the University of Wisconsin and got his M.D. from Northwestern University in Chicago Illinois.

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What is Hypothyroidism?

Hypothyroidism is a medical condition characterized by reduced thyroid hormone production by the thyroid gland.  This gland sits in the front of the lower portion of the neck and plays a critical role in human metabolism.  Low thyroid hormone levels result in a reduced metabolic rate, leading to findings such as slow heart rate (bradycardia), fatigue, mental fogginess, weight gain, constipation, diabetes, elevated cholesterol, and cold intolerance.  Most cases of hypothyroidism are due to autoimmune destruction of the thyroid hormone producing cells – known as Hashimoto’s thyroiditis.

Patients with severe forms of hypothyroidism may develop a condition called myxedema coma – this disease can be fatal if left untreated.  In extreme cases, patients may also develop cardiogenic shock due to the inability of the heart muscle to create and utilize energy from food.

What Causes Hypothyroidism?

Most cases of hypothyroidism are caused by Hashimoto’s thyroiditis. This condition occurs when patients form autoantibodies that attack proteins in the thyroid.  This may initially result in increased thyroid hormone production due to thyroid inflammation. Over time the thyroid tissue is damaged and thyroid hormone production naturally falls.  Patients eventually develop symptoms of hypothyroidism: fatigue, weight gain, and cold intolerance.  Patients with Hashimoto’s disease are at increased risk of developing other autoimmune conditions.

Other causes of hypothyroidism are less common and may include:

  • Pregnancy
  • Iodine deficiency
  • Thyroid removal (surgery)
  • Radioactive iodine ablation

Pregnancy can lead to temporary hypothyroidism as the growing fetus requires a large amount of thyroid hormone to develop properly. Thyroid hormone is made from iodine and a lack of iodine in the diet will lead to hypothyroidism. This is far more common in developing countries and rarely occurs in the United States. Thyroid removal and intentional destruction with radioactive materials is done in patients who have overactive thyroids that are leading to hyperthyroidism. 

How common is Hypothyroidism?

Hypothyroidism is common in the United States. The U.S. Center for Disease Control estimates that 4.6% of the U.S. population is living with hypothyroidism. Some of these cases are “subclinical” meaning that they only result in mild symptoms and may go undetected. All forms of hypothyroidism are more common in women, some forms such as pregnancy induced hypothyroidism only occur in women. 


Signs and Symptoms

The most common symptom of hypothyroidism is fatigue, nearly all patients that are symptomatic report feeling fatigued. There are many other symptoms of hypothyroidism but the majority of these are only present in moderate to severe cases. The most common symptoms of hypothyroidism are: 

  • Fatigue
  • Mental fogginess – memory loss or confusion
  • Constipation – slowed gastrointestinal motility
  • Cold intolerance
  • Depressed mood
  • Numbness & tingling in the extremities – peripheral neuropathy
  • Swelling in the legs

The Signs of hypothyroidism are generally absent in patients with mild hypothyroidism but those with moderate and severe hypothyroidism typically present with the following signs:

  • Slow heart rate (bradycardia)
  • Increased weight
  • Delayed relaxation phase of deep tendon reflexes
  • Memory impairment
  • Lower extremity edema

Hypothyroidism can have many complications if untreated. Some of these are slowly progressive such as weight gain, diabetes, elevated cholesterol, peripheral neuropathy, and dementia. However other complications can develop rapidly and lead to sudden and rapid illness. Some of these more severe complications are bradycardia, heart failure, depression, coma, and death.


The diagnosis of hypothyroidism is typically suspected based on the symptoms listed above. This suspicion is always confirmed with thyroid function studies such as thyroid stimulating hormone (TSH) and thyroid hormone (free T4).  Your doctor may also order thyroperoxidase antibodies (TPO antibodies) – these indicate that you have autoantibodies against the thyroid gland (Hashimoto disease).

Other commonly ordered blood tests include a CMP (comprehensive metabolic panel), CBC (complete blood cell count).  They will also usually check your cholesterol levels and screen for diabetes.  Women of childbearing age are typically screened for pregnancy with a urine test.

If your heart rate is slow (bradycardic) your doctor will likely obtain an ECG (electrocardiogram).  If you have symptoms or signs of heart failure, they will likely obtain a chest x-ray and ultrasound of the heart (echocardiogram). An ultrasound of the thyroid may also be performed if there is a suspicion for any nodules or abnormalities of the thyroid gland. 

Hypothyroidism Medication and Treatment

Hypothyroidism is treated with thyroid hormone – Synthroid (levothyroxine). This medication is dosed based on body weight and adjusted based on the TSH levels at your repeat visits.  The starting dose is generally smaller in elderly patients and those with kidney disease.  The medication should be taken on an empty stomach first thing in the morning to ensure proper drug absorption. Failure to take thyroid hormone properly and on a regular schedule can lead to the rapid return of hypothyroidism and its damaging complications. 

Patients are typically reassessed in 4-6 weeks for symptoms and TSH levels.  The Synthroid (levothyroxine) dose is either reduced, kept the same, or increased depending on symptoms and TSH.

Patients with severe hypothyroidism or complications of hypothyroidism such as myxedema coma typically require hospitalization with endotracheal intubation (to protect their airway).  They may also require the use of norepinephrine or dopamine intravenous drips to maintain heart rate and blood pressure.  Treatment with intravenous levothyroxine and corticosteroids is curative and patients that improve and that are extubated are eventually transitioned to oral levothyroxine.


  1. Canaris GJ, Manowitz NR, Mayor G, Ridgway EC. The Colorado thyroid disease prevalence study. Arch Intern Med 2000; 160:526. - https://jamanetwork.com/journals/jamainternalmedicine/fullarticle/415184
  2. Rugge JB, Bougatsos C, Chou R. Screening and treatment of thyroid dysfunction: an evidence review for the U.S. Preventive Services Task Force. Ann Intern Med 2015; 162:35. - https://www.ncbi.nlm.nih.gov/pubmed/25347444
  3. Jonklaas J, Bianco AC, Bauer AJ, et al. Guidelines for the treatment of hypothyroidism: prepared by the american thyroid association task force on thyroid hormone replacement. Thyroid 2014; 24:1670. - https://www.ncbi.nlm.nih.gov/pubmed/25266247


Drugs for Hypothyroidism

The above information is an educational aid only. It is not intended as medical advice for individual conditions or treatments. Talk to your doctor, nurse or pharmacist before following any medical regimen to see if it is safe and effective for you.