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 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 – this disease is called 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, requiring vasopressors to maintain hemodynamic stability.
What Causes Hypothyroidism?
Most causes of hypothyroidism are caused by Hashimoto’s disease - in this disease, patients form autoantibodies that attack proteins in the thyroid. This may initially result in increased thyroid hormone production due to thyroid inflammation – with time, the thyroid ultimately begins reducing hormone production. Patients eventually develop symptoms of hypothyroidism – fatigue, weight gain, 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:
- Iodine deficiency
- Thyroid removal (surgery)
- Radioactive iodine ablation
Complications of hypothyroidism in include weight gain, diabetes, elevated cholesterol, peripheral neuropathy, dementia, bradycardia, heart failure, depression, and fatigue. Severe cases may lead to coma and even death.
How common is Hypothyroidism?
Hypothyroidism is exceedingly common in the United States and responsible for frequent primary care visits. The most common cause is Hashimoto disease. Severe or complicated cases often require referral to an endocrinology specialist.
About 0.1%-2% of people have hypothyroidism. Subclinical hypothyroidism has an even higher prevalence, varying from 4%-10% of adults. Hypothyroidism is 5-8 times more common in women in comparison to men.
Signs and Symptoms
There are number of patients who have biochemical evidence of hypothyroidism with elevated TSH levels, but normal free T4 levels and no symptoms of hypothyroidism. This condition is referred to as subclinical hypothyroidism.
Hypothyroidism is characterized by elevated TSH and low free T4 levels. Symptoms often include:
- 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
Signs of hypothyroidism typically include:
- Slow heart rate (bradycardia)
- Increased weight
- Delayed relaxation phase of deep tendon reflexes
- Memory impairment
- Lower extremity edema
Patients with severe forms of hypothyroidism may be in a coma called myxedema coma. Patient may also present in cardiogenic shock.
The diagnosis of hypothyroidism is suggested based on symptoms and physical examination, but typically 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 EKG (electrocardiogram). If you have symptoms or signs of heart failure, they will likely obtain a chest x-ray and ultrasound of the heart (echocardiogram).
Occasionally, you doctor will order an ultrasound of the thyroid gland if they feel thyroid nodules.
Hypothyroidism Medication and Treatment
Hypothyroidism is treated with thyroid hormone – Synthroid (levothyroxine). Your doctor will typically start you on a dose depending on your weight. 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.
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 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 Synthroid.
- 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
- 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
- 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
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.