Hypothyroidism (Underactive Thyroid): Symptoms, Causes, and Treatment

What is Hypothyroidism (Underactive Thyroid): Symptoms, Causes, and Treatment?

Hypothyroidism, or underactive thyroid, is when the thyroid gland in the neck does not make enough thyroid hormone. This hormone sets the speed of the body, so symptoms include tiredness, weight gain, feeling the cold, dry skin, constipation and low mood. In the United States, the United Kingdom and Australia the most common cause is an autoimmune condition called Hashimoto's disease. It is more common in women and in people over 60. Diagnosis is a blood test that measures thyroid-stimulating hormone (TSH) and free thyroxine (free T4). Treatment is a daily tablet of levothyroxine, a man-made copy of the natural hormone, with follow-up blood tests to fine-tune the dose. Overt hypothyroidism affects roughly 3 in 1,000 adults and a milder form (subclinical hypothyroidism) about 4 in 100.

Symptoms

Early symptoms

• Tiredness and low energy: Feeling drained, sluggish or sleepy during the day, even after a full night's sleep, is the most common symptom. It usually builds up slowly over months. (1) (3) (4) (9)
• Weight gain: Modest weight gain, often 2 to 5 kilograms, with no change in diet. It happens because a low hormone level slows the metabolism and the body holds on to fluid. (1) (5) (8)
• Feeling cold: Being cold when other people are comfortable, especially in the hands and feet. Low thyroid hormone lowers the amount of heat the body makes. (1) (4) (7)
• Dry skin and dry, thinning hair: Skin may feel rough or flaky and hair may feel brittle or fall out more than usual. Eyebrows can thin at the outer edge. (1) (5) (9)
• Constipation: The gut moves more slowly, so bowel movements become less frequent and harder to pass. (3) (5) (8)
• Low mood and poor concentration: Low thyroid hormone can cause sadness, loss of interest, and a foggy feeling with poor memory or slow thinking. This can be mistaken for depression on its own. (1) (7) (9)
• Hoarse voice and a puffy face: The voice can become deeper or croaky and the face, eyelids and hands may look puffy because of fluid build-up under the skin. (1) (9)
• Muscle aches, cramps and weakness: Aching or stiff muscles and joints, cramps, and reduced grip strength are common. Some people get carpal tunnel syndrome, which is tingling in the hand. (5) (9)
• Heavy or irregular periods: In women, periods can become heavier, longer or less regular. An underactive thyroid can also make it harder to become pregnant. (1) (7)
• Slow heartbeat and raised cholesterol: The pulse can be slower than normal and blood cholesterol often rises. Both usually return to normal once treatment starts. (9) (3)

Serious or emergency symptoms

• Becoming very drowsy, confused or hard to wake: A severe, long-untreated underactive thyroid can lead to a rare emergency called myxoedema coma. Warning signs are extreme drowsiness or confusion, a very low body temperature, a slow pulse and slow, shallow breathing. It is often set off by cold weather, an infection, surgery or missed medication. Call the emergency services now: 911 in the United States, 999 in the United Kingdom, or 000 in Australia. This condition needs hospital treatment and is fatal in about 1 in 4 to 1 in 2 people even with intensive care. (1) (9) (3)
• New swelling at the front of the neck (goitre): An enlarged thyroid can cause visible swelling in the lower neck and, rarely, a feeling of pressure when swallowing or breathing. Book an urgent appointment with your doctor for examination and a blood test. (1) (5)

Causes

Primary causes

• Hashimoto's disease (autoimmune thyroiditis): The immune system makes antibodies that slowly damage the thyroid. This is the most common cause in the United States, the United Kingdom and Australia and other countries where people get enough iodine. It often runs in families and can occur with other autoimmune conditions. (1) (3) (8) (9)
• Iodine deficiency: The thyroid needs iodine to make its hormone. Too little iodine in the diet is the leading cause of hypothyroidism worldwide, though it is uncommon in countries that add iodine to salt. (3) (5) (9)
• Thyroid surgery: Removing all or part of the thyroid, for example to treat a nodule, goitre or cancer, lowers or stops hormone production. (1) (4) (5)
• Treatment for an overactive thyroid: Radioactive iodine or anti-thyroid medicine used to treat an overactive thyroid, including Graves' disease, commonly leads to an underactive thyroid afterwards, often within a year. (1) (4) (9)
• Radiotherapy to the head or neck: Radiation treatment for cancers of the head, neck or upper chest can damage the thyroid months to years later. (5) (4) (9)

Contributing factors

• Medicines: Lithium, amiodarone, interferon and some modern cancer immunotherapy drugs can reduce thyroid hormone production. Tell your doctor about every medicine you take. (4) (3) (9)
• Pregnancy-related (postpartum) thyroiditis: About 1 in 10 women develop thyroid inflammation in the year after giving birth. It can cause a temporary underactive thyroid that recovers on its own, though some women need lasting treatment. (9) (4)
• A problem with the pituitary gland (central hypothyroidism): Rarely, the thyroid is normal but the pituitary gland in the brain does not send it the signal to work. This is called central or secondary hypothyroidism and needs specialist assessment. (9) (3)
• Congenital hypothyroidism (present from birth): Some babies are born with a thyroid that did not form or work properly. In the United States, the United Kingdom and Australia every newborn is screened with a heel-prick blood test so treatment can start early. (3) (9) (8)

Risk factors

Diagnosis

Hypothyroidism is diagnosed with a blood test, not from symptoms alone. The first test is thyroid-stimulating hormone (TSH). When the thyroid is underactive the pituitary gland releases more TSH to push it, so a high TSH is the earliest signal. If TSH is high, the laboratory usually also measures free thyroxine (free T4). A high TSH with a low free T4 confirms overt hypothyroidism. A high TSH with a normal free T4 is called subclinical, or mild, hypothyroidism. Many laboratories treat a TSH above about 4 to 5 mU/L as above range, but the exact cut-off varies between laboratories and with age. A mildly abnormal result is normally repeated after 2 to 3 months before a diagnosis is made, because short illnesses can affect thyroid blood tests. Testing for thyroid peroxidase (TPO) antibodies can show that Hashimoto's disease is the cause. This TSH-led approach is the same in United States guidance from the American Thyroid Association, United Kingdom guidance from the NHS and NICE, and Australian guidance from the RACGP.

Treatment

Medication options

Lifestyle and self-care

• Take the tablet the same way every day: A steady routine keeps the hormone level even. Pick a time you can keep to, on an empty stomach, and use a pill box or phone reminder if it helps. (4) (8)
• Eat a normal balanced diet and avoid iodine supplements: No food or supplement cures an underactive thyroid. You do not need a special diet. Avoid kelp, seaweed and high-dose iodine supplements unless your doctor advises them, as too much iodine can make thyroid problems worse. (6) (2) (4)
• Tell every clinician and pharmacist that you take levothyroxine: Several common medicines and supplements change how much levothyroxine you absorb, so your dose may need checking when other treatments start or stop. (4) (10)
• Keep your monitoring blood tests: Regular TSH checks make sure the dose stays right. Needs change with weight, age, pregnancy and other illnesses. (2) (6)
• Plan ahead if you might become pregnant: The dose usually needs to go up early in pregnancy. If you are planning a pregnancy, ask your doctor to check your thyroid first and to review it as soon as you know you are pregnant. (4) (9)

Always discuss dosing and treatment changes with your own prescriber.

Possible complications

• Heart and cholesterol problems: Untreated hypothyroidism raises LDL cholesterol and blood pressure and, over time, the risk of heart disease. Severe long-standing disease can cause heart failure and a build-up of fluid around the heart. (2) (9) (3)
• Goitre: Long-term lack of thyroid hormone can make the gland enlarge, causing a swelling in the neck that may feel uncomfortable or affect swallowing. (2) (5)
• Fertility and pregnancy problems: An underactive thyroid can make it harder to conceive. In pregnancy, untreated or undertreated hypothyroidism raises the risk of miscarriage, pre-eclampsia, premature birth, low birth weight and effects on the baby's brain development. With treatment and monitoring these risks fall close to normal. (4) (9) (3)
• Nerve and mental-health effects: Some people develop nerve compression such as carpal tunnel syndrome, or ongoing low mood and slowed thinking, which usually improve with treatment. (9) (2)
• Myxoedema coma: A rare, life-threatening emergency in severe untreated disease, with a very low body temperature, drowsiness progressing to unconsciousness, and slow breathing. It needs immediate hospital care. (1) (9)

When to see a doctor

Routine follow-up

• Book a routine appointment if you have ongoing symptoms such as tiredness, weight gain, feeling cold, constipation, dry skin or low mood, so a thyroid blood test can be done. These symptoms have many causes and a test is the only way to know. (1) (8)
• See your doctor if you already take levothyroxine and your symptoms come back, get worse, or new ones appear, as your dose may need adjusting. (2) (6)
• Contact your doctor promptly if you are pregnant or planning a pregnancy and have thyroid disease or thyroid symptoms, because the dose often needs to change early in pregnancy. (4) (9)

Seek emergency care

• Call the emergency services now, 911 in the United States, 999 in the United Kingdom or 000 in Australia, if a person with a known or suspected underactive thyroid becomes very drowsy, confused or unresponsive, feels very cold to the touch, or is breathing very slowly. This may be myxoedema coma, which is a medical emergency. (1) (9) (3)

Frequently asked questions

References

1. NHS — Underactive thyroid (hypothyroidism) source 1
2. NHS — Underactive thyroid: living with source 2
3. MedlinePlus (US National Library of Medicine) — Hypothyroidism source 3
4. American Thyroid Association — Hypothyroidism (patient information) source 4
5. Mayo Clinic — Hypothyroidism (underactive thyroid): Symptoms & causes source 5
6. Mayo Clinic — Hypothyroidism (underactive thyroid): Diagnosis & treatment source 6
7. Cleveland Clinic — Hypothyroidism source 7
8. healthdirect (Australia) — Hypothyroidism source 8
9. StatPearls / NCBI Bookshelf — Hypothyroidism source 9
10. US FDA — Synthroid (levothyroxine sodium) Prescribing Information source 10