Hypothyroidism is a condition in which the thyroid gland does not produce enough thyroid hormone. It is the most common thyroid disorder.
The Thyroid gland
The thyroid gland is situated in front of the neck just above the clavicles. It is responsible for producing thyroid hormones. The two important hormones produced by the thyroid gland are T3 or triiodothyronine and T4 or thyroxine.
Another very important hormone is TSH or thyroid stimulating hormone which is produced by the pituitary gland in the brain.
TSH is responsible for the regulation of thyroid function through its negative feedback effect. When thyroxine is released in an insufficient amount, TSH is released by the pituitary which stimulates the thyroid gland to produce more hormones.
Similarly, this stimulatory effect is lost when the thyroid gland is overactive.
What causes Hypothyroidism?
Hypothyroidism can be primary or secondary.
Primary hypothyroidism is insufficient production of thyroid hormones by the thyroid gland due to a problem in the thyroid gland itself. It may be caused by autoimmune thyroid disease, Thyroiditis, surgery or Drugs.
Clinical manifestations in both primary and secondary or central hypothyroidism are the same.
What are the symptoms of Hypothyroidism?
Symptoms of hypothyroidism vary from subtle or no symptoms at all to life-threatening. Since the thyroid hormone affects almost every system of the body, symptoms are not localized to a specific system.
Since the thyroid hormones are responsible for maintaining and regulating metabolic activities of the body, symptoms of hypothyroidism reflect slowing of all the metabolic processes of the body.
Hypothyroidism leads to a decrease in sweat production. The skin may become dry and thick. The hair may become coarse or thin, eyebrows may disappear, and nails may become brittle.
Patients with hypothyroidism can develop mild swelling around the eyes and can have thinning of eyebrows especially the lateral one third.
Effects on the Cardiovascular system:
Patients with hypothyroidism can have elevated blood pressure especially the diastolic blood pressure leading to narrow pulse pressure. The heart rate becomes slow as well as the heart contractions.
Patients may have pericardial effusion which is the accumulation of fluid around the heart. Cholesterol levels are raised predisposing the patient to atherosclerotic heart diseases. Patients may develop exercise intolerance, shortness of breath and fatigue.
Effects on the Lungs:
Hypothyroidism weakens the respiratory muscles and decreases lung function.
Symptoms can include fatigue, shortness of breath with exercise, and decreased ability to exercise. Hypothyroidism can also lead to swelling of the tongue, hoarse voice, and sleep apnea.
Sleep apnea is a condition in which there is intermittent blockage of the airway while sleeping, causing fitful sleep and daytime sleepiness. Patients may also develop pleural effusions.
Effects on the Gastrointestinal system:
Hypothyroidism slows the actions of the digestive tract, causing constipation. Rarely, the digestive tract may stop moving entirely called ileus.
Effect on the Reproductive system:
Women with hypothyroidism often have menstrual cycle irregularities, ranging from absent or infrequent periods to very frequent and heavy periods.
The patient may be visiting a gynecologist for infertility. Occasionally, patients are diagnosed with Hypothyroidism while being investigated for infertility.
Furthermore, pregnant women with hypothyroidism have an increased risk for miscarriage during early pregnancy. Treatment of hypothyroidism can decrease these risks.
In people with severe hypothyroidism, trauma, infection, exposure to the cold, and certain medications can rarely trigger a life-threatening condition called myxedema coma, which causes a loss of consciousness and hypothermia (low body temperature).
How to diagnose Hypothyroidism?
In the past, hypothyroidism was not diagnosed until symptoms had been present for a long time. However, simple blood tests can now detect the disease at an early stage.
A person may be tested for hypothyroidism if there are signs and symptoms, such as those discussed above, or as a screening test.
Blood tests can confirm the diagnosis and pinpoint the underlying cause of thyroid hormone deficiency. The most common blood test for hypothyroidism is TSH (thyroid stimulating hormone).
TSH is the most sensitive test because it can be elevated even with small decreases in thyroid function.
Thyroxine (T4), the main product of the thyroid gland, may also be measured to confirm and assess the degree of the disease.
Routine screening for Hypothyroidism:
Screening for thyroid diseases is mandatory in neonates in certain parts of the world. Screening is not routinely done in Pakistan but high-risk patients especially babies who are hypoactive and have developmental delay must be screened.
In adults screening of general population is not recommended but patients who have fertility issues, weight gain, are diabetics or have other endocrine disorders are usually tested for the disease.
How to treat Hypothyroidism?
The goal of treatment is to return blood levels of TSH and T4 to the normal range and to alleviate symptoms.
The treatment is thyroid hormone replacement therapy. This is usually given orally.
Thyroxine should be taken once per day on an empty stomach (one hour before eating or two hours after). Thyroxine is available in Pakistan as Thyroxine, Thyronorm, and Eltroxin.
However, it is preferable to stay on the same type of thyroxine rather than switching between brands and/or generic formulations.
If a switch is necessary, a blood test is usually done six weeks later to determine if the dose needs to be adjusted.
In most cases, symptoms of hypothyroidism begin to improve within two weeks of starting thyroid replacement therapy. However, people with more severe symptoms may require several months of treatment before they fully recover.
Duration and dose of Thyroxine:
Hypothyroidism requires lifelong treatment. Patients may be advised to repeat TSH after 6 weeks initially and be followed.
Normal results do not indicate that the disease has been cured.
Normal TSH is an indirect assessment of optimal dose. Also, a normal TSH does not mean that the same dose is to be taken for life.
With changes in body composition, weight, and age, the thyroxine dose needs to be adjusted.
So monitoring initially after 6 weeks, followed by three months and then half yearly to yearly, depending on the patient’s comorbid conditions and symptoms.
Self-adjustment of Thyroxine dose can be a little tricky!
Self-adjustment of thyroxine dose can be tricky since a high TSH is an indicator of increasing thyroxine dose and a low TSH suggests a reduction in thyroxine dose.
A self-dose adjustment may lead to hyperthyroidism which may affect the heart and weaken the bones ( osteoporosis) or reduction in dose may lead to worsening of the original symptoms.
When to adjust the thyroxine dose?
Changes in the T4 dose are based upon the person’s TSH and T4 level. The dose may need to be increased if thyroid disease worsens, during pregnancy, if gastrointestinal conditions impair T4 absorption, or if the person gains weight.
A high fiber diet, calcium- or aluminum-containing antacids, and iron tablets can interfere with the absorption of T4 and should be taken at a different time of day.
The dose may need to be decreased as the person gets older, after childbirth, or if the person loses weight.
Monitoring of Thyroid status:
Individual T4 doses can vary widely and depend upon a variety of factors, including the underlying cause of hypothyroidism. People with certain conditions require more frequent monitoring.
Advanced age and heart disease:
Thyroid hormone makes the heart work a bit harder. Therefore, a clinician may opt for more conservative T4 treatment in older adults and in people with coronary artery disease.
Hypothyroidism in Pregnancy:
Women often need higher doses of T4 during pregnancy. Testing is usually recommended every four weeks, beginning after conception.
Once the optimal T4 dose is established, testing is usually repeated at least once per trimester. After delivery, the woman’s dose of T4 will need to be adjusted again.
Hypothyroidism in Surgical patients:
Hypothyroidism can increase the risk of certain surgery-related complications; bowel function may be slow to recover and infection may be overlooked if there is no fever.
If pre-operative blood tests reveal low thyroid hormone levels, non-emergency surgery is usually postponed until treatment has returned T4 levels to normal.
Subclinical Hypothyroidism or Hypothyroidism without symptoms:
In some cases, hypothyroidism is extremely mild or causes no obvious symptoms (called subclinical hypothyroidism). The decision to treat subclinical disease with T4 is controversial.
Many experts treat patients with subclinical hypothyroidism if their TSH is >10 mU/L to prevent the development of a full-blown disease and associated symptoms.
Treatment is also recommended for people who have a goiter or nonspecific symptoms of hypothyroidism, such as fatigue, constipation, or depression.