Hypothyroidism refers to an underactive thyroid gland that doesn’t produce enough of the thyroid hormones T3 and T4. This can lead to a variety of symptoms including fatigue, weight gain, dry skin, hair loss, cold sensitivity, constipation and depression among others. Hypothyroidism is a common condition, affecting around 4.6% of the U.S. population. There are several potential causes of hypothyroidism, but the number one cause is Hashimoto’s thyroiditis, an autoimmune disease.
What is Hashimoto’s Thyroiditis?
Hashimoto’s thyroiditis, also known as chronic lymphocytic thyroiditis, is the most common cause of hypothyroidism in the United States. It is an autoimmune disorder in which the body’s immune system mistakenly attacks the thyroid gland, leading to inflammation and damage that impairs the gland’s ability to produce sufficient thyroid hormone.
Some key facts about Hashimoto’s thyroiditis:
– It is 5-10 times more common in women than men.
– Onset is typically between ages 30-50, but can occur at any age.
– There is often a genetic/family link. Having a family member with Hashimoto’s increases your risk.
– The hallmark is the production of antibodies that target the thyroid. These include thyroid peroxidase antibodies (TPOAb) and thyroglobulin antibodies (TgAb).
– The thyroid gland becomes infiltrated with white blood cells, gradually leading to hypothyroidism in the majority of patients.
– Hashimoto’s is the most common cause of goiter (thyroid enlargement).
– It often goes undiagnosed initially as symptoms can be vague. Regular screening of thyroid function is important for at-risk groups.
– There is no cure, but thyroid hormone replacement therapy is effective at managing symptoms by replacing the hormones the thyroid can no longer produce.
Top Causes of Hypothyroidism
The main causes of hypothyroidism include:
1. Hashimoto’s Thyroiditis
As discussed above, Hashimoto’s thyroiditis is by far the number one cause accounting for 90% or more of cases in the United States. It is an autoimmune disorder that damages the thyroid so it does not produce adequate thyroid hormone.
2. Thyroiditis
Thyroiditis refers to thyroid inflammation and includes conditions like postpartum thyroiditis and subacute thyroiditis. These may temporarily impair thyroid function and cause temporary hypothyroidism.
3. Thyroid Surgery
Total or partial removal of the thyroid gland can cause hypothyroidism. This may be done to treat thyroid cancer, nodules, or hyperthyroidism. Patients require thyroid hormone replacement following thyroid surgery.
4. Radiation Therapy
Radiation used to treat cancers of the head and neck can affect the thyroid. This may lead to hypothyroidism months or years later in some patients.
5. Congenital Hypothyroidism
Babies can sometimes be born with an underactive thyroid or no thyroid at all. Causes include problems with thyroid development in the womb or genetic disorders. All newborns should be screened.
6. Iodine Deficiency
Consuming inadequate iodine can reduce thyroid hormone production and cause hypothyroidism, especially in developing parts of the world. Iodine is added to salt in the U.S. to prevent deficiency.
7. Medications
Certain medications like lithium, interferon alpha, and interleukin-2 can impact thyroid function and may induce hypothyroidism.
8. Pituitary disorders
The pituitary gland produces TSH to stimulate the thyroid. Diseases of the pituitary gland may disrupt this relationship and cause hypothyroidism.
9. Pregnancy
The high hormone levels of pregnancy naturally cause increased thyroid hormone demands. Hypothyroidism can surface during or after pregnancy in susceptible women.
Symptoms
Hypothyroidism develops gradually, so symptoms may be subtle at first. They become more noticeable as the condition progresses. Common symptoms include:
– Fatigue
– Increased sensitivity to cold
– Constipation
– Dry skin and hair
– Unexplained weight gain
– Muscle weakness
– Muscle cramps and aches
– Depression
– Impaired memory and concentration
– Abnormal menstrual cycles
– Reduced heart rate
– Goiter (enlarged thyroid gland)
Keep in mind many symptoms are non-specific and could be attributed to other conditions. The only way to confirm hypothyroidism is through blood tests measuring thyroid hormones.
Risk Factors
A number of factors can increase the risk of developing hypothyroidism:
– Female gender – women are 5-8 times more likely than men
– Increasing age – risk rises over age 50
– Autoimmune disease – family history or personal history
– Pregnancy – postpartum thyroiditis occurs in 5-10% of women after giving birth
– Radiation exposure – radiation therapy to the neck region
– Thyroid surgery – partial or full removal of thyroid gland
– Smoking has been linked to increased risk
– Certain medications – lithium, amiodarone, interferons
– Iodine deficiency or excess
– Selenium deficiency
Diagnosis
Diagnosing hypothyroidism involves blood tests measuring levels of thyroid stimulating hormone (TSH) and thyroid hormones T3 and T4. Common findings include:
– Elevated TSH – TSH rises in an attempt to stimulate more thyroid hormone production. Levels above 4.5-5.0 mU/L are considered abnormal.
– Low free T4 – levels below 0.8-1.0 ng/dL indicate hypothyroidism
– Elevated cholesterol – due to reduced clearance from lack of thyroid hormones
– Positive antibodies – Hashimoto’s thyroiditis is associated with anti-TPO and anti-thyroglobulin antibodies
If Hashimoto’s is suspected, an ultrasound of the thyroid may reveal an enlarged gland with a heterogeneous texture.
Treatment
Treatment for hypothyroidism involves replacing the thyroid hormone that your own thyroid can no longer produce adequately through medication.
– The standard treatment is levothyroxine (synthetic T4). The dose is adjusted based on regular monitoring of TSH and T4 levels.
– T3/T4 combination therapy may be beneficial for some patients not responding sufficiently to levothyroxine alone.
– Older infants and children require higher dosing per body weight than adults.
– Treatment is lifelong for permanent hypothyroidism.
– Managing Hashimoto’s may also include anti-inflammatory medications, thyroid-protective nutrients, and stress management.
Complications of Untreated Hypothyroidism
Leaving hypothyroidism uncorrected can result in several complications:
– Goiter – chronic stimulation of the thyroid can lead to gradual enlargement.
– Heart problems – increased risk of heart failure, atherosclerosis, abnormal heart rhythms.
– Mental health issues – progression of depression, dementia.
– Peripheral neuropathy – nerve damage leading to numbness and tingling.
– Carpal tunnel syndrome
– Increased cholesterol and atherosclerosis.
– Myxedema – life-threatening state involving low heart rate, hypothermia, fluid buildup.
– Birth defects – untreated hypothyroidism in pregnancy poses risks to fetal neurocognitive development.
– Infertility – women with hypothyroidism often have irregular or absent periods and reduced fertility.
That is why proper screening and management of hypothyroidism is important, especially for those at higher risk like the elderly, women, and those with autoimmune disease.
Can Hypothyroidism Be Prevented?
It’s not always possible to prevent hypothyroidism, but the following measures can reduce risk in some cases:
– Carefully manage autoimmune disorders like Hashimoto’s under a doctor’s supervision. Follow treatment plans to help prevent progressive thyroid damage.
– Avoid overconsumption of foods that impair thyroid function – cruciferous vegetables, soy, gluten.
– Make sure to get adequate selenium and iodine from dietary sources. Supplement if deficient.
– Maintain a healthy weight. Obesity is linked to increased risk.
– Avoid smoking and tobacco use.
– Limit alcohol. Excess alcohol impacts thyroid function.
– Protect against radiation exposure. Use protective collars during dental x-rays.
– Discuss pros/cons of PTU vs methimazole if antithyroid drug therapy required for hyperthyroidism. PTU has lower risk of causing hypothyroidism later on.
While not always preventable, being informed about risk factors and symptoms allows early detection and treatment if hypothyroidism does develop.
Conclusion
In summary, Hashimoto’s thyroiditis is the leading cause of hypothyroidism, accounting for 90% or more of cases in the U.S. It is an autoimmune condition that damages the thyroid gland, impairing its ability to produce thyroid hormone. Hypothyroidism produces a wide range of symptoms that can be vague initially but become more overt over time. Blood tests measuring TSH and thyroid hormone levels are needed to confirm the diagnosis. With proper detection and levothyroxine treatment, most patients with hypothyroidism can manage their symptoms effectively. Regular screening and being aware of risk factors allows for early diagnosis and prevention of complications from low thyroid hormones.