Hypothyroidism (Underactive Thyroid)

Hypothyroidism, also known as an underactive thyroid, is a medical condition where the thyroid gland does not produce enough thyroid hormones. These hormones are essential for regulating the body's metabolism, meaning that insufficient levels lead to a generalized slowing of metabolic processes. In severe, long-standing cases, it may be referred to as myxedema. There are different types of hypothyroidism: Overt (Clinical) Hypothyroidism: This is diagnosed when thyroid-stimulating hormone (TSH) levels are high and free thyroxine (FT4) levels are low. Subclinical Hypothyroidism: This occurs when TSH levels are high, but FT4 levels remain within the normal range. Central Hypothyroidism: This type is caused by problems with the pituitary or hypothalamus glands, which control the thyroid. It is characterized by low FT4 levels and TSH levels that are not appropriately elevated (they can be low, normal, or slightly high). Congenital Hypothyroidism: This refers to thyroid hormone deficiency that is present at birth.

Symptoms

Fatigue, lethargy, lack of energy
Weight gain (often modest, 5-10 lbs, mostly fluid)
Cold intolerance
Dry skin and hair
Hair loss (including eyebrows, especially the outer third)
Constipation
Muscle aches, weakness, and cramps
Menstrual irregularities (e.g., heavy periods/menorrhagia)
Bradycardia (slow heart rate)
Goiter (enlarged thyroid gland)
Depression, low mood
Cognitive dysfunction ('brain fog'), memory problems, poor concentration
Hoarseness or deepening of the voice
Puffy face (myxedema), especially around the eyes (periorbital edema)
Peripheral neuropathy (numbness, tingling in hands/feet)
Delayed relaxation of deep tendon reflexes
Decreased libido
Infertility
Carpal tunnel syndrome
Sleep apnea
Galactorrhea (due to high TRH stimulating prolactin)
Altered mental status (confusion, lethargy, psychosis, coma) - Emergency symptom
Severe hypothermia (body temperature <35.5°C / 95.9°F) - Emergency symptom
Hypoventilation - Emergency symptom
Hypotension - Emergency symptom
Hypoglycemia - Emergency symptom
Hyponatremia - Emergency symptom

Causes & Risk Factors

Autoimmune disease (Hashimoto's Thyroiditis), where the immune system attacks the thyroid gland
Surgical removal of part or all of the thyroid gland (thyroidectomy)
Radiation therapy, such as radioactive iodine treatment for hyperthyroidism or external radiation for head and neck cancers
Congenital hypothyroidism, where a baby is born with an absent or poorly functioning thyroid gland
Pituitary gland dysfunction (secondary hypothyroidism), leading to insufficient TSH production
Hypothalamic dysfunction (tertiary hypothyroidism), leading to insufficient thyrotropin-releasing hormone (TRH) production
Iodine deficiency (most common cause worldwide)
Certain medications, including amiodarone, lithium, interferon-alpha, and tyrosine kinase inhibitors
Infiltrative diseases like amyloidosis, sarcoidosis, or hemochromatosis
Transient hypothyroidism, which can occur in subacute (de Quervain's) thyroiditis or postpartum thyroiditis
Age, particularly over 60 years
Being female (more common in women)
Personal or family history of autoimmune diseases (e.g., Type 1 diabetes, celiac disease, rheumatoid arthritis) or thyroid disease
Genetic syndromes such as Down syndrome or Turner syndrome
History of postpartum thyroiditis or goiter
Iodine deficiency or excess
Previous radioactive iodine (RAI) therapy for hyperthyroidism
Previous thyroid surgery (thyroidectomy)
External beam radiation therapy to the head, neck, or chest
Use of certain medications, including amiodarone, lithium, interferon-alpha, and tyrosine kinase inhibitors
Postpartum period, increasing the risk of postpartum thyroiditis
Possible environmental exposures to certain chemicals like perchlorate and polychlorinated biphenyls (PCBs), though evidence is evolving

Diagnosis

Review of symptoms (e.g., fatigue, weight gain, cold intolerance)
Assessment of personal medical history, including autoimmune diseases, prior thyroid surgery or radiation
Evaluation of family history of thyroid or autoimmune disorders
Review of current and past medications
Obstetric history in women
Physical examination of the thyroid gland for size (goiter), consistency, and nodules
Assessment of skin and hair for dryness, coarseness, hair loss, and pallor
Cardiovascular examination for bradycardia or distant heart sounds
Neurological examination to test deep tendon reflexes for delayed relaxation phase (Woltman's sign)
General assessment for facial puffiness, periorbital edema, and non-pitting edema (myxedema)
Primary screening test: Serum Thyroid-Stimulating Hormone (TSH). High TSH suggests primary hypothyroidism. Low or inappropriately normal TSH with low FT4 suggests central hypothyroidism.
Confirmatory test: Free Thyroxine (FT4 or T4). Low FT4 confirms overt hypothyroidism. Normal FT4 with high TSH indicates subclinical hypothyroidism.
Thyroid Peroxidase (TPO) Antibodies test to confirm Hashimoto's thyroiditis as an autoimmune cause.
Overt Hypothyroidism is diagnosed when TSH is above the reference range AND FT4 is below the reference range.
Subclinical Hypothyroidism is diagnosed when TSH is above the reference range AND FT4 is within the reference range.
During pregnancy, TSH reference ranges are lower, with trimester-specific ranges recommended (e.g., First trimester: <2.5 mIU/L, or population-based ranges if available).
Differential diagnosis considers conditions like euthyroid sick syndrome, depression, chronic fatigue syndrome, anemia, kidney disease, and adrenal insufficiency.
NICE guidelines recommend measuring TSH alone for initial testing. If TSH is elevated, repeat TSH with FT4. If TSH is within the reference range, further FT4 testing is not needed.
ATA/AACE guidelines state TSH is the single best screening test for primary thyroid dysfunction for most outpatient clinical situations.

Treatment Options

Levothyroxine (L-T4) monotherapy is the standard first-line treatment.
Levothyroxine dosing typically starts at a weight-based dose (e.g., 1.6 mcg/kg/day in healthy adults) or a lower dose in elderly patients or those with cardiac disease (e.g., 25-50 mcg/day).
Levothyroxine should be taken on an empty stomach, 30-60 minutes before breakfast or at bedtime (at least 3 hours after the last meal), with water.
Levothyroxine should be separated from supplements like calcium and iron by at least 4 hours.
Dessicated Thyroid Extract (DTE) is not recommended by major organizations due to inconsistent hormone levels and lack of long-term safety data.
Combination T4/T3 therapy is controversial and generally not recommended for routine use, but may be considered for patients with persistent symptoms on L-T4 monotherapy with normal TSH levels.
For subclinical hypothyroidism, treatment is debated. Guidelines generally recommend treatment if TSH > 10 mIU/L. For TSH levels between the upper limit of normal and 10 mIU/L, treatment may be considered based on symptoms, presence of TPO antibodies, goiter, or plans for pregnancy.
Myxedema coma is a medical emergency requiring ICU admission.
Emergency treatment for myxedema coma includes intravenous (IV) levothyroxine and/or liothyronine, IV hydrocortisone (until coexisting adrenal insufficiency is ruled out), and supportive care (e.g., passive rewarming, mechanical ventilation).
TSH levels should be checked 6-8 weeks after starting therapy or changing a dose.
The goal of treatment is to maintain TSH within the reference range (typically 0.4-4.0 mIU/L, though some aim for 0.5-2.5 mIU/L).
Once TSH levels are stable, they should be monitored annually.
Referral to a specialist is indicated for pregnancy or planning pregnancy, patients under 18 years old, individuals with cardiac disease, presence of a goiter or nodule, difficulty achieving stable TSH levels, or suspected central hypothyroidism.

Frequently Asked Questions

What is the difference between hypothyroidism and Hashimoto's disease?

Hypothyroidism is the general medical condition where your thyroid gland doesn't produce enough hormones. Hashimoto's disease (or Hashimoto's thyroiditis) is the most common autoimmune cause of hypothyroidism, where your immune system mistakenly attacks and damages your thyroid gland.

Do I need to follow a special diet for my hypothyroidism?

The research dossier does not specify a special diet for hypothyroidism, beyond ensuring adequate iodine intake. Iodine is crucial for thyroid hormone production, and both deficiency and excess can affect thyroid function.

Should I avoid certain foods like soy or cruciferous vegetables?

The provided research dossier does not contain specific recommendations to avoid foods like soy or cruciferous vegetables for hypothyroidism.

Will I have to take medication for the rest of my life?

In most cases, such as with Hashimoto's disease or after thyroid surgery, hypothyroidism is a permanent condition that requires lifelong medication. However, some forms of transient hypothyroidism, like postpartum thyroiditis, may resolve, though there's a higher risk of developing permanent hypothyroidism later.

Why do I still feel tired even though my TSH levels are normal?

Even with normal TSH levels on levothyroxine therapy, some individuals may experience persistent symptoms like fatigue. If symptoms continue, your doctor may consider other factors or discuss alternative treatment approaches, such as combination T4/T3 therapy, though its use is controversial.

Is it safe to take levothyroxine during pregnancy?

Yes, it is safe and crucial to take levothyroxine during pregnancy. Untreated or undertreated hypothyroidism during pregnancy can lead to increased risks for both the mother (e.g., miscarriage, preeclampsia) and the baby (e.g., preterm birth, impaired neurocognitive development).

Will my medication dose need to change during pregnancy?

Yes, your levothyroxine dose will likely need to change during pregnancy. TSH reference ranges are lower during pregnancy, and your doctor will monitor your thyroid levels closely to adjust your medication as needed to support both your health and your baby's development.

Can hypothyroidism cause weight gain, and will treatment help me lose weight?

Hypothyroidism can cause modest weight gain, often due to fluid retention. With appropriate levothyroxine treatment, symptoms typically improve within a few weeks, and this can include a reduction in the weight gained due to hypothyroidism.

What is the best time of day to take my thyroid medication?

Levothyroxine should be taken on an empty stomach, either 30-60 minutes before breakfast or at bedtime (at least 3 hours after your last meal), with water. This helps ensure proper absorption of the medication.

What happens if I miss a dose of my medication?

The provided research dossier does not explicitly state what to do if a dose of levothyroxine is missed. You should consult your healthcare provider for specific instructions.

Are natural or desiccated thyroid treatments better than synthetic levothyroxine?

Major medical organizations like the American Thyroid Association (ATA) and the American Association of Clinical Endocrinologists (AACE) do not recommend desiccated thyroid extract (DTE). This is due to inconsistent hormone levels and a lack of long-term safety data compared to synthetic levothyroxine.

Can I take my thyroid medication with my other medications or supplements?

It is important to separate your thyroid medication from certain supplements, such as calcium and iron, by at least 4 hours. Always discuss all your medications and supplements with your doctor or pharmacist to avoid interactions.

How often do I need to have my thyroid levels checked?

After starting levothyroxine therapy or changing a dose, your TSH levels should be checked after 6-8 weeks. Once your levels are stable and within the target range, annual monitoring of TSH is typically recommended.

Does hypothyroidism cause hair loss, and will it grow back?

Yes, hair loss, including thinning of the eyebrows (especially the outer third), is a common symptom of hypothyroidism. With consistent and appropriate treatment, symptoms typically improve, and hair growth can return, though full resolution may take several months.

Can hypothyroidism affect my mood or cause depression?

Yes, hypothyroidism can affect your mood and is associated with symptoms like depression and a low mood. If left untreated or undertreated, it can contribute to long-term neurological issues, including cognitive impairment and depression.

What is the difference between T4 and T3?

Thyroxine (T4) and triiodothyronine (T3) are the two main hormones produced by your thyroid gland. Levothyroxine (L-T4) is the synthetic form of T4, which is the primary hormone replaced in treatment. T3 is a more active form of the hormone, often converted from T4 in the body.

Should my doctor be testing my Free T3 levels?

Free T3 levels are not routinely recommended for the diagnosis of hypothyroidism according to most guidelines. The primary tests for diagnosis and monitoring are TSH and Free T4.

Are my symptoms due to my thyroid or something else?

Many symptoms of hypothyroidism, such as fatigue and depression, can overlap with other conditions. Your doctor will consider a differential diagnosis, which may include conditions like depression, chronic fatigue syndrome, anemia, kidney disease, or adrenal insufficiency, to determine the true cause of your symptoms.

Can hypothyroidism affect my cholesterol levels or heart health?

Yes, untreated or undertreated hypothyroidism can significantly impact your cardiovascular health. It is associated with an increased risk of heart disease, high cholesterol (dyslipidemia), high blood pressure (hypertension), and heart failure.

What is subclinical hypothyroidism and does it need to be treated?

Subclinical hypothyroidism is characterized by an elevated TSH level but normal free thyroxine (FT4) levels. Treatment for subclinical hypothyroidism is debated. Guidelines generally recommend treatment if TSH is above 10 mIU/L. For TSH levels between the upper limit of normal and 10 mIU/L, treatment may be considered based on individual factors like symptoms, presence of TPO antibodies, goiter, or plans for pregnancy.

Will my children be at risk for developing thyroid problems?

If there is a personal or family history of autoimmune diseases or thyroid disease, your children may have an increased risk. Universal newborn screening for congenital hypothyroidism is standard in many countries to detect and treat the condition early.

Can stress affect my thyroid function?

The provided research dossier does not explicitly detail the impact of stress on thyroid function.

Are there any lifestyle changes I can make to support my thyroid health?

Ensuring adequate dietary iodine intake, for example through iodized salt or iodine-rich foods, is a key lifestyle factor that supports thyroid health and is the most effective primary prevention strategy globally.