Thyroid Disease

What the thyroid does

The thyroid makes two hormones, thyroxine (T4) and triiodothyronine (T3), which set the speed of metabolism in nearly every cell, affecting heart rate, energy, body temperature, weight, bowel habits, mood and periods. The pituitary gland controls the thyroid with thyroid-stimulating hormone (TSH). When thyroid hormone is low, TSH rises; when thyroid hormone is high, TSH falls. Iodine from food is essential for making thyroid hormone.

Types of thyroid disease

Hypothyroidism (underactive thyroid)

Hypothyroidism is the most common thyroid disorder. The main US cause is Hashimoto's thyroiditis, an autoimmune attack on the gland. Others include thyroid surgery, radioactive iodine treatment, some medicines (amiodarone, lithium) and, worldwide, iodine deficiency.

Hyperthyroidism (overactive thyroid)

Hyperthyroidism is most often caused by Graves' disease, an autoimmune condition. Other causes are toxic adenoma and toxic multinodular goiter, thyroiditis, and too much thyroid hormone medicine.

Goiter and nodules

A goiter is an enlarged thyroid. Thyroid nodules are lumps within the gland, found in many adults on ultrasound. More than 90% of nodules are benign.

Thyroiditis

Inflammation of the thyroid, including postpartum thyroiditis and painful subacute thyroiditis after viral infections, often causes a temporary overactive phase followed by an underactive phase.

Thyroid cancer

Thyroid cancer usually presents as a painless nodule. Most types, especially papillary cancer, have an excellent outlook.

Symptoms: underactive vs overactive

Thyroid disease in women

Women are 5 to 8 times more likely than men to have thyroid problems. Thyroid disease can cause irregular or heavy periods, fertility problems and miscarriage risk. Pregnancy increases thyroid hormone needs, so people on levothyroxine usually need a dose increase as soon as pregnancy is confirmed. Postpartum thyroiditis affects some women in the year after giving birth. Symptoms around menopause can overlap with thyroid symptoms, so testing helps sort them out.

Risk factors

• female sex
• age over 60
• family history of thyroid disease
• other autoimmune conditions: type 1 diabetes, celiac disease, rheumatoid arthritis, lupus, vitiligo, Addison's disease
• Down syndrome and Turner syndrome
• previous radiation to the neck, thyroid surgery or radioactive iodine
• medicines such as amiodarone and lithium

Diagnosis

• TSH: the best single screening test.
• Free T4 (and T3 in suspected hyperthyroidism).
• Antibodies: TPO antibodies for Hashimoto's; TSH receptor antibodies for Graves'.
• Thyroid ultrasound for goiter and nodules.
• Radioactive iodine uptake scan to identify the cause of hyperthyroidism.
• Fine-needle aspiration biopsy of suspicious nodules.

Treatment

Hypothyroidism

Levothyroxine (synthetic T4) taken once daily, usually on an empty stomach. The dose is adjusted with TSH tests every 6 to 8 weeks until stable, then yearly. Take it apart from calcium, iron and antacids, which reduce absorption.

Hyperthyroidism

• Antithyroid medicines: methimazole (or propylthiouracil in early pregnancy).
• Beta-blockers to control fast heart rate and tremor.
• Radioactive iodine to shrink overactive tissue.
• Surgery (thyroidectomy) for large goiters, nodules, cancer or when other treatments are unsuitable.

Radioactive iodine and surgery often lead to hypothyroidism, treated with levothyroxine.

Nodules and cancer

Benign nodules are usually monitored. Cancer is treated with surgery, sometimes followed by radioactive iodine and thyroid hormone therapy.

Complications if untreated

• Hypothyroidism: high cholesterol, heart disease, infertility, depression, and rarely myxedema coma.
• Hyperthyroidism: atrial fibrillation, heart failure, bone loss (osteoporosis), and rarely thyroid storm.
• In pregnancy: miscarriage, preterm birth and effects on the baby's development.

Frequently asked questions

What are the first signs of thyroid problems?

Common early signs of an underactive thyroid are tiredness, weight gain, feeling cold, constipation and dry skin. An overactive thyroid often starts with a racing heart, weight loss, anxiety, heat intolerance and tremor. A neck lump or swelling can also be a first sign.

What is the difference between hypothyroidism and hyperthyroidism?

Hypothyroidism means the thyroid makes too little hormone, slowing the body down. Hyperthyroidism means it makes too much, speeding the body up. They have opposite symptoms and different treatments.

How is thyroid disease diagnosed?

A blood test for TSH is the main screening test, usually with free T4. Antibody tests, ultrasound, uptake scans and biopsies help identify the cause and check nodules.

Can thyroid disease be cured?

Some forms can be cured, such as thyroid cancer removed with surgery or hyperthyroidism treated with radioactive iodine or surgery, though lifelong levothyroxine is then often needed. Hashimoto's hypothyroidism is usually lifelong but easily controlled with daily medicine.

Why is thyroid disease more common in women?

Autoimmune thyroid diseases, the main causes, are much more common in women, likely because of hormonal and immune differences. Pregnancy and the postpartum period are also times when thyroid problems often appear.