Hypothyroidism is a common chronic endocrine disorder characterized by thyroxine underproduction. Of the worldwide population, 5% have been diagnosed with the disorder, and experts from the National Library of Medicine estimate that another 5% remain undiagnosed. This post will review thyroid anatomy, relevant symptoms, the diagnosis, and management of hypothyroidism.
Thyroid Anatomy and Terminology
The thyroid is a butterfly-shaped organ located at the junction of the trachea and larynx. Its two lobes are connected anteriorly by the isthmus, which spans the trachea. The thyroid gland contains colloid-filled follicles that synthesize the protein thyroglobulin. Thyroglobulin then binds to iodine to form triiodothyronine (T3) and tetraiodothyronine (T4). T4 is also known as thyroxine.
The hypothalamic-pituitary-thyroid axis regulates thyroid hormone release. The brains hypothalamus produces a thyrotropin-releasing hormone (TRH), which passes into the anterior pituitary gland. TRH stimulates the pituitary gland to release a thyroid-stimulating hormone (TSH).
TSH, in turn, prompts the thyroid to produce more thyroxine. In the functioning of a healthy thyroid, the gland produces the correct amount of thyroid hormones to promote homeostasis and help the body maintain many of its daily processes, such as:
- Bone growth
- Energy levels
- Internal temperature regulation
- Metabolism
- Muscle maintenance
In the case of hypothyroidism, the thyroid gland is unable to produce enough hormones to allow for daily metabolic function.
Symptoms of Hypothyroidism
Patients with suspected or confirmed hypothyroidism may report the following symptoms:
- Bradycardia
- Brain fog
- Brittle nails
- Cold intolerance
- Constipation
- Depression
- Dry skin
- Goiter development
- Heavy or irregular menstruation
- Infertility
- Joint and muscle pain
- Lethargy
- Thinning hair
- Weight gain
Healthcare providers should note that hypothyroidism occurs more often in females than in males. Additionally, patients over 60 years of age and those with celiac disease, diabetes mellitus, rheumatoid arthritis, or lupus are more likely to develop this disorder.
What Causes Hypothyroidism?
There are many causes of hypothyroidism. Both genetic and environmental components seem to play a role in the organs development and its efficacy in hormone production.
Congenital hypothyroidism
Congenital hypothyroidism occurs when a patient is born with thyroid hypoplasia or agenesis. It can also occur when thyroid-attacking antibodies pass from mother to fetus, preventing the thyroid from developing normally. If left untreated, the defect can cause jaundice, stunted growth, and mental disabilities, among other complications. The condition can manifest with or without a diffuse nontoxic goiter.
Hypothyroidism due to medications and substances
The adverse effects of drugs or toxins can prevent the thyroid from producing hormones. For example, clinical studies have shown that amiodarone and lithium can cause thyroid disorders.
Myxedema coma
Myxedema coma is a severe form of hypothyroidism that can be lethal. Myxedema describes swelling of the face, eyelids, tongue, and larynx, as well as low basal metabolic rate and body temperature.
This condition occurs when the homeostatic mechanisms of a patient with hypothyroidism become disrupted. The American Family Physician provides examples of disruptions that include stroke, trauma, or infection, such as pneumonia or sepsis.
Postinfectious hypothyroidism
Hypothyroidism can also result from infection. The inflamed thyroid may not be able to produce adequate amounts of hormones. After prolonged inflammation, the damaged thyroid may not fully recover.
Postprocedural hypothyroidism
Postprocedural hypothyroidism is the result of a partial or total impairment of the thyroid due to medical intervention. This is usually conducted by surgical or radiological means, such as in the treatment of thyroid cancer.
Thyroid atrophy
Thyroid atrophy involves the shrinkage or degeneration of thyroid tissue. An atrophied thyroid may become nonviable or severely limited in its functioning. Acquired thyroid atrophy develops over time and is often the result of years of inflammation, an autoimmune disease (e.g., autoimmune thyroiditis or Hashimotos thyroiditis), or long-term infection.
How is Hypothyroidism Diagnosed?
The efficacy of thyroid function is analyzed through blood tests. Abnormally high amounts of TSH and low concentrations of T4 in the blood are often used to identify hypothyroidism, as they indicate an imbalance in the hypothalamic-pituitary-thyroid axis.
General normal ranges for T3, T4, and TSH tests for adults are as follows:
- T3: 100-200 nanograms per deciliter (ng/dL)
- T4: 5.0-12.0 micrograms (g)/dL
- TSH: 0.4-4.0 milli-international units per liter (mIU/L)
Pregnant patients and patients with a history of thyroid cancer or disease have different normal ranges.
Hypothyroidism Treatment and Management
Hypothyroidism is generally treated with hormone replacement therapy. Daily doses of levothyroxine supply the body with thyroxine and allow for normal metabolic function.
Levothyroxine can be synthetic or zoonotic in origin. The medication is usually administered orally as a tablet, soft gel, or liquid. In extreme cases of hypothyroidism, such as myxedema coma, it may be delivered intravenously.
According to the Food and Drug Administration (FDA), the following medications are approved brand names of tablet and capsule levothyroxine medication:
- Levo-T
- Levothroid
- Levothyroxine sodium
- Levoxyl
- Synthroid
- Tirosint
- Unithroid
Zoonotic levothyroxine (made from desiccated bovine or porcine thyroid) supplement brand names include Armour, NatureThyroid, and NP Thyroid.
It is very important that healthcare providers educate patients on certain supplements and medications that can interfere with levothyroxine absorption. Calcium, iron, and aluminum hydroxide are a few examples. Additionally, studies show that levothyroxine absorption is most effective on an empty stomach.
While in treatment, the healthcare professional, the patient, and/or the caregiver should be aware of changes to vital signs (e.g., tachycardia, arrhythmia, palpitations, bradycardia), sleep disturbances (e.g., insomnia), mental status (e.g., anxiety), appetite, and energy levels. The goal of treatment is to bring the TSH, T3, and T4 into normal ranges so that adverse symptoms decrease.
Conclusion
Hypothyroidism is a common endocrine disorder that can affect the quality of life of patients. With proper treatment, it is manageable. Early diagnosis and detection are key to reducing the symptoms and effects of hypothyroidism.
References:
Alkabban, F. M., Patel, B. C. (2023). Nontoxic Goiter. In StatPearls. StatPearls Publishing. https://www.ncbi.nlm.nih.gov/books/NBK482274/
American Thyroid Association. (n.d.) Thyroid Hormone Treatment. American Thyroid Association. https://www.thyroid.org/thyroid-hormone-treatment/
Chiovato, L., Magri, F., & Carlé, A. (2019). Hypothyroidism in Context: Where We've Been and Where We're Going. Advances in therapy, 36(Suppl 2), 4758. https://doi.org/10.1007/s12325-019-01080-8
Kotwal, A., Brown, R., LaFranchi, S., & Rose, S. (2022). Congenital Hypothyroidism. Endocrine Society. https://www.endocrine.org/patient-engagement/endocrine-library/congenital-hypothyroidism
Mayo Clinic Staff. (2022). Hypothyroidism (underactive thyroid). Mayo Clinic. https://www.mayoclinic.org/diseases-conditions/hypothyroidism/diagnosis-treatment/drc-20350289
Shahid M. A., Ashraf M. A., & Sharma S. (2023). Physiology, Thyroid Hormone. In StatPearls. StatPearls Publishing. https://www.ncbi.nlm.nih.gov/books/NBK500006/
Shine, B., McKnight, R. F., Leaver, L., & Geddes, J. R. (2015). Long-term effects of lithium on renal, thyroid, and parathyroid function: a retrospective analysis of laboratory data. Lancet (London, England), 386(9992), 461468. https://doi.org/10.1016/S0140-6736(14)61842-0
Trohman, R. G., Sharma, P. S., McAninch, E. A., & Bianco, A. C. (2019). Amiodarone and thyroid physiology, pathophysiology, diagnosis and management. Trends in cardiovascular medicine, 29(5), 285295. https://doi.org/10.1016/j.tcm.2018.09.005
U.S. Department of Health and Human Services. (n.d.). Hashimotos Disease. National Institute of Diabetes and Digestive and Kidney Diseases. https://www.niddk.nih.gov/health-information/endocrine-diseases/hashimotos-disease
U.S. Department of Health and Human Services. (n.d.). Hypothyroidism (underactive thyroid) - NIDDK. National Institute of Diabetes and Digestive and Kidney Diseases. https://www.niddk.nih.gov/health-information/endocrine-diseases/hypothyroidism#causes
U.S. Food and Drug Administration. (2015). Table of Approved Levothyroxine Sodium Oral Formulations (Tablet or Capsule). U.S. Food and Drug Administration. https://www.fda.gov/drugs/postmarket-drug-safety-information-patients-and-providers/table-approved-levothyroxine-sodium-oral-formulations-tablet-or-capsule
Wall C. R. (2000). Myxedema coma: diagnosis and treatment. American Family Physician, 62(11), 24852490. https://www.aafp.org/pubs/afp/issues/2000/1201/p2485.html
About the Author:
Savannah Schmidt is a medical content writer and editor with five years of professional experience. She has a BA in English Literature and has had a hand in creating, editing, and publishing over 500 pieces of content for CEUs for healthcare and medical coding professionals.
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