Hypothyroidism

Hypothyroidism is a condition in which the thyroid gland does not make enough thyroid hormone. This hormone sets the pace at which nearly every cell works, so a shortage makes the body seem to run slowly: tiring easily, feeling cold, constipation, dry skin, slight weight gain, and sluggish thinking. Symptoms develop gradually over months to years, so they are often blamed on tiredness or aging. In some people, the first clue actually comes from the heart, such as a slow heart rate, getting short of breath easily during activity, or cholesterol that is suddenly high on a routine checkup. Hypothyroidism belongs to the group of thyroid disorders, covered on the Thyroid Disorders page.

Common Causes

In areas with adequate iodine intake, a frequent cause is Hashimoto's thyroiditis, an autoimmune inflammation that slowly damages the thyroid gland. Other causes include surgery to remove the thyroid, radioactive iodine therapy, radiation to the neck, iodine deficiency, and certain medicines such as amiodarone, lithium, and some cancer drugs. In babies, hypothyroidism can be present from birth (congenital hypothyroidism) and is detected through heel-prick blood spot screening a few days after birth.

Effects on the Heart and Blood Vessels

A shortage of thyroid hormone weakens the contractions of the heart muscle and slows the heart rate. Blood vessels become stiffer, so the lower (diastolic) blood pressure number can rise. LDL cholesterol and triglycerides tend to increase, which over time speeds up plaque buildup, as covered on the Dyslipidemia page. In severe, long-standing hypothyroidism, fluid can collect in the sac around the heart, covered on the Pericardial Effusion page. People with heart failure can also get worse when their thyroid hormone levels are low.

Subclinical Hypothyroidism

Sometimes a blood test shows a slightly high TSH with a still-normal FT4. This is called subclinical hypothyroidism. Not everyone needs treatment right away: your doctor weighs the TSH level, symptoms, age, the presence of thyroid antibodies, heart disease, and pregnancy plans. In overt hypothyroidism, a replacement hormone taken every day usually restores hormone levels, and many of the changes in the heart and cholesterol improve as well. In older adults and people with coronary artery disease, the starting dose is usually kept small and then raised slowly so the heart is not overloaded.

Your doctor asks about your symptoms, any history of thyroid surgery or treatment, the medicines you take, pregnancy plans, and family history, then examines your neck, skin, pulse, blood pressure, and reflexes. The diagnosis is confirmed with TSH and FT4 blood tests. Because the symptoms are not specific, these tests are also recommended for people with newly found high cholesterol, heart failure, or a slow heart rate with no clear cause.

If the results are only slightly outside the normal range, your doctor usually repeats the test in a few weeks to months, because TSH levels can change temporarily, for example during a serious illness. An anti-TPO antibody test helps confirm Hashimoto's. Heart tests such as an ECG, echocardiography, and a lipid profile assess the effect on the heart and also serve as a baseline for follow-up once treatment is under way.

See a doctor if several of the following symptoms persist for a few weeks. Hypothyroidism symptoms come on slowly, so they are easy to miss.

• Constant tiredness and sleepiness even with enough sleep
• Feeling cold easily, dry skin, hair loss, and constipation
• Weight gain without a change in eating habits
• Slow heart rate or getting short of breath easily during activity
• Newly found high cholesterol
• Heavy periods, difficulty getting pregnant, or planning a pregnancy with a history of thyroid problems
• A baby with prolonged jaundice, poor feeding, and a lot of sleeping

Go to the emergency room right away if you become so sleepy that you are hard to wake, your body feels very cold, your breathing is slow, or you have chest pain after starting thyroid hormone.