What Is the Thyroid Gland?
The thyroid gland is an endocrine or hormone-secreting gland located in the neck. It is vital for production, storage, and secretion of two thyroid hormone – thyroxine (T4) and triiodothyronine (T3). Thyroid hormones regulate the use of energy in the body.
Hypothyroidism means too little hormone in the blood.
Hyperthyroidism means too much thyroid hormone in the blood.
The regular thyroid gland ( shaped like a butterfly) has two lobes connected by an isthmus and occasionally, a small pyramidal lobe rising upward from the isthmus. The thyroid gland is located in the lower part of the neck, in front of the windpipe (trachea). The thyroid gland moves with swallowing and is often visible, especially when it becomes enlarged. Understandably, the thyroid gland is more easily seen in people with long, thin necks than in people with short, thick necks. Ordinarily, the thyroid gland weighs less than an ounce and has the consistency of muscle. The right lobe of the thyroid gland is often slightly larger than the left lobe.
When viewed under the microscope, the thyroid gland is composed of distinct units called follicles. Follicles make and store thyroid hormone. Follicles store thyroid hormones attached to a protein called thyroglobulin (Tg). Malignant tumors arising from follicular cells are called differentiated (papillary or follicular) or undifferentiated (anaplastic) thyroid cancer.
What Is Thyroid Disease?
Thyroid disease is very common. In fact, it affects more than thirty million Americans. Unfortunately, more than thirteen million Americans have a thyroid condition and are unaware of it. Women are much more likely than men are to have thyroid disease. For reasons that are unclear, approximately 80% of all thyroid disease occurs in women. Regardless of the reasons, women in particular should be aware of the signs and symptoms of thyroid disease as well as the impact it can have on their well-being.
Overall, thyroid diseases may be viewed as disorders of structure and disorders of function. Since disorders of function and structure frequently overlap it is common for patients to have more than one thyroid problem.
What is Hypothyroidism?
Hypothyroidism is too little thyroid hormone in the blood. We refer to it as an underactive thyroid. This disease affects a minimum of six million Americans and one out of every 4,000 newborns. Women are much more likely to have hypothyroidism than men are.
Hypothyroidism may be permanent and require a lifetime of thyroid hormone replacement, or it may be transient (temporary) and require little if any, treatment.
Regardless of the cause of hypothyroidism, treatment is safe, simple, and very effective.
Symptoms of Hypothyroidism
There are many signs and symptoms of hypothyroidism. Individual hypothyroid patients may have none, some, or many of these signs and symptoms, depending on the severity of their disease. These signs and symptoms are often present in other conditions as well. Therefore, hypothyroidism cannot be diagnosed by signs and symptoms alone. The diagnosis can only be confirmed after a thorough medical history, physical examination, and the appropriate laboratory tests.
The most common complaints voiced by hypothyroid patients are fatigue, excessive sleepiness, memory loss, hair loss, and feeling cold (cold intolerance). Weight gain may occur, but it is minimal. Some patients may notice that they are having more trouble maintaining their usual weight.
When hair loss (alopecia) occurs, it may be a very discouraging experience. Hair loss can be caused by many things other than hypothyroidism, such as stress, hyperthyroidism, and in women, too much male hormone. Hair lost from hypothyroidism will grow back within three to six months after successful treatment of hypothyroidism.
Hypothyroidism may cause menstrual abnormalities and infertility. But meanwhile, it is not the most common cause of either. A patient with hypothyroidism may have a milky breast discharge (galactorrhea), and the patient’s interest in sex (libido) may decrease.
Both depression and hypothyroidism are common, especially in women. Furthermore, hypothyroidism can aggravate symptoms of depression, although it does not ordinarily cause depression. Therefore, it is possible, and not at all unusual, for patients to have both hypothyroidism and depression. If hypothyroid patients are also depressed, it is sometimes difficult to get well without treating both their depression and their hypothyroidism.
Signs and Symptoms of Hypothyroidism
• feeling tired and slow constipation
• feeling cold
• numbness of hands
• husky voice
• muscle cramps
• drowsiness during the day
• slow heart rate
• excessive sleepiness
Testing for Hypothyroidism
An elevated TSH and a low free T4 confirm the diagnosis of primary hypothyroidism. These test results, however, do not predict the severity of a patient’s symptoms.
In addition to TSH and free T4, antithyroid antibodies (TPOAb and TgAb) are commonly measured to determine if hypothyroid patients have Hashimoto’s thyroiditis. It is important to make the diagnosis of Hashimoto’s thyroiditis since this autoimmune disorder is hereditary, is associated with other autoimmune diseases, and virtually assures that hypothyroidism will be permanent.
Not all patients with elevated TSH levels are hypothyroid. Certain unusual conditions can cause elevation of TSH. For example, people with resistance to thyroid hormone, a rare hereditary disease, may have elevated TSH levels along with elevated thyroid hormone levels. Patients with resistance to thyroid hormone have unusual and confusing thyroid function test results. It is important that they are accurately diagnosed to avoid unnecessary treatment. The need for an accurate diagnosis also applies to patients with TSH-producing pituitary tumors who may have similarly misleading TSH test results.
Screening Patients for Hypothyroidism
Screening, an important tool in preventive medicine, is a process for detecting disease among people who do not have symptoms of a disease or who are unaware that they may have a disease. Screening newborns for congenital hypothyroidism has been very successful and widely accepted. Some physicians recommend screening groups of people known to be at increased risk of developing thyroid disease, such as women over thirty-five, men over fifty-five, people with Down’s syndrome, and people with autoimmune diseases, such as Type 1 diabetes.
Causes of Hypothyroidism
Hypothyroidism may be permanent and require a lifetime of thyroid hormone replacement, or it may be transient (temporary) and require little if any, treatment. Hashimoto’s thyroiditis, an autoimmune disease affecting 5% of the adult population, is the most common cause of hypothyroidism in the United States.
Most Common Causes of Permanent Hypothyroidism
• Hashimoto’s thyroiditis
• Radioactive iodine treatment of hyperthyroidism frequently results in permanent hypothyroidism.
• Surgical removal of the thyroid gland (thyroidectomy) can also result in permanent hypothyroidism if sufficient thyroid tissue is removed.
• Iodine deficiency is the most common cause of hypothyroidism in the world.
Causes of Transient (Temporary) Hypothyroidism
The most common cause use of transient hypothyroidism is thyroiditis. Subacute thyroiditis, postpartum thyroiditis, and painless thyroiditis can cause temporary hypothyroidism. In most cases of transient thyroiditis, treatment with thyroid hormone replacement is not necessary. However, some patients with transient thyroiditis, especially painless thyroiditis, will develop permanent hypothyroidism and require a lifetime of thyroid hormone treatment.
In many ways, treatment of hypothyroid patients represents the best that medicine has to offer. Since hypothyroidism is the deficiency of thyroid hormone, the procedure is very clear and straightforward—thyroid hormone replacement. Brand-name levothyroxine is the drug of choice. Once the diagnosis of permanent hypothyroidism is confirmed, patients must take levothyroxine every day for the rest of their lives. Regardless of the cause of hypothyroidism, the treatment is safe, simple, and very effective.
The onset of hypothyroidism is slow and insidious. Similarly, a full response to treatment occurs gradually and may take six weeks or longer. Therefore, hypothyroid patients should not expect immediate improvement, even if their initial dosage of levothyroxine is correct. Re-examination of patients and repeat thyroid function tests are ordinarily performed six to twelve weeks after initiation of therapy with levothyroxine. If adjustments of the dosage are made, patients will be examined and tested again in another six to twelve weeks.
Treatment Options for Subclinical Hypothyroidism
Many endocrinologists believe that untreated subclinical hypothyroidism can adversely affect overall health and, therefore, should be treated. Potential reasons to treat patients with subclinical hypothyroidism may include one or more of the following:
• prevention of progression to overt hypothyroidism
• reduction of cholesterol levels
• reduction in cardiovascular disease risk
• improvement in the treatment of depression
• treatment of fertility
• prevention of intellectual impairment in children born to inadequately treated hypothyroid mothers
The treatment of patients with subclinical hypothyroidism is the same as that of patients with overt hypothyroidism – levothyroxine therapy. Although, patients with subclinical hypothyroidism do not have symptoms of hypothyroidism, they may feel better after treatment with levothyroxine. They may not have noticed their symptoms until the symptoms were gone. Other patients do not notice any improvement in the way they feel. For example, tests done before and after treatment revealed improvement of dry skin, low energy, cold intolerance, memory, anxiety, and signs of depression.
As previously discussed, depression and hypothyroidism share many symptoms, and one disease may mask the other. Since abnormal thyroid function may be more common in patients suffering from depression, it is logical to test the thyroid function of depressed patients. Even mild thyroid failure can interfere with the treatment of depression. For example, antidepressants do not work as effectively in patients with subclinical hypothyroidism as compared to euthyroid patients who are depressed. Therefore, levothyroxine therapy is usually recommended for patients who are suffering from depression and have elevated TSH levels.