Thyroid Problems – Types, Causes, Diagnosis (Tests), Treatment

Posted by Dr. Chris

The thyroid gland is a large gland located in the front of the neck. Most of us know it for being the gland that controls the metabolism which simply means the amount of energy that the body produces. Since energy is produced by breaking down food, we know that a person with a high thyroid activity will be thinner and a person with low thyroid activity will have more fat. However, the thyroid gland and the hormones it secretes has a wide range of effects beyond just weight gain or loss. Any disturbance in thyroid activity can even be life threatening.

What are thyroid problems?

Thyroid problems is a broad term for any number of disorders of the thyroid gland or its hormones. It does not specifically indicate the type of problem with thyroid function yet many people commonly use the word ‘thyroid problems’ for various thyroid diseases. Simply, thyroid problems can mean that the thyroid activity is low or high. This may also mean that the thyroid gland is underactive or overative.

Yet the problem is not always with the thyroid gland itself. Sometimes it involves the thyroid hormones of which there is two – triiodothyronine (T3) and thyroxine (T4). Understanding the differences between low and high thyroid activity is important as the symptoms can vary and is often opposite to each other.

Thyroid Problems Gland and Hormones

There are different causes of thyroid problems depending on the type of problem. It is important to first know how the thyroid gland works to be able to understand the different types of problems and causes.

Thyroid Gland

The thyroid gland is located just below the voice box (larynx) and just in front of the windpipe (trachea). Although a fairly large gland, it weighs only 15 to 20 grams in adults. It has two lobes (left and right) connected by an isthmus. There many compartments known as follicles within the gland. The thyroid hormones are stored inside these follicles by attaching to a protein known as thyroglobulin. Thyroid hormones are stored in this way for 2 to 3 months. Most thyroid problems involve the thyroid gland or thyroid hormones but sometimes the problem can arise from the way the thyroid gland is controlled and monitored.

Picture of thyroid gland from Wikimedia Commons.

Thyroid Control

A portion in the brain is constantly monitoring the level of thyroid hormones in the blood. This area is known as the hypothalamus. When the thyroid hormone levels are too low, the hypothalamus releases its own hormone known as thyrotropin-releasing hormone (TRH). This TRH then acts on another gland known as the pituitary gland located towards the front of the brain. TRH causes the pituitary gland to release its own thyroid controlling hormone known as thyroid-stimulating hormone (TSH). This TSH then travels through the blood and stimulates the thyroid gland to produce more thyroid hormones and to secrete more thyroid hormones into the bloodstream.

Thyroid Hormones

There are two thyroid hormones – triiodothyronine (T3) and thyroxine (T4). Both these hormones are similar in chemical structure except for one additional iodide in T4. Most of the thyroid hormone released by the thyroid gland is T4. Just before it is used, T4 is converted to T3. The main effects of the thyroid hormones on the body are to increase the rate of various processes such as :

Energy production
Protein synthesis
Glucose utilization
Carbohydrate absorption from the gut
Fat release from the fatty tissue

Thyroid hormones also have various other effects like altering the heart rate, the amount of blood pumped out of the heart, growth, sleep, sexual function and menstrual cycle. However, since thyroid hormones affect every cell in the body it can affect any other system as well.

Thyroid Problems Causes

Autoimmune
Nutritional deficiency or excess of iodine
Iatrogenic – surgery, radiation and medication
Genetic defects
Birth defects
Pituitary gland dysfunction
Hypothalamic disorders
Growths like nodules and benign tumors
Cancer
Unknown causes (idiopathic)

Underactive Thyroid Problems

Underactive thyroid problems means that the activity of the thyroid gland or thyroid hormones is lower than normal. Sometime the thyroid gland is not being stimulated sufficiently to produce and release thyroid hormones because of a problem with the pituitary gland or hypothalamus. This is known as hypothyroidism.

The types of underactive thyroid problems discussed below are known as primary hypothyroidism in that the problem lies in the thyroid gland or the thyroid hormones. Secondary hypothyroidism is where the problem lies in the pituitary gland or hypothalamus and the thyroid gland is usually normal.

Hashimoto’s thyroiditis

Hashimoto’s thyroiditis is inflammation of the thyroid gland which occurs when the immune system attacks it. It is therefore known as an autoimmune disease and is a common cause of hypothyroidism, especially among women.

Iodine deficiency

Iodine is needed to make thyroid hormone. When it is lacking in the diet or in the body then there is less thyroid hormones available. Since the body cannot produce iodine, it has to get it from foods. These days many foods are fortified with iodine, like table salt, to ensure that there is a sufficient supply.

Radiation

Radiation therapy may be used to treat cancers either in the thyroid gland or surrounding organs. The thyroid gland may be damaged when irradiated. Sometimes radioactive iodine is used to shrink the thyroid gland but this can also cause under-functioning of the entire gland.

Medication

Certain medication can affect thyroid gland function directly or indirectly by upsetting the control of the thyroid function. This includes drugs such as :

Lithium
Iodides
Anti-tuberculosis drugs like p-aminosalicylic acid

Surgery

A thyroidectomy is a type of surgery where part of the thyroid gland or the entire gland is removed usually in certain types of thyroid cancers. If a small part of the thyroid gland is removed it may not affect normal function. Once a large part or the entire gland is removed than thyroid activity is lower than normal.

Birth defects

There are various types of developmental problems with the thyroid gland that occurs in fetal life. It is often linked to genetic defects.

Thyroid dysgenesis is where the thyroid gland fails to develop, is severely underdeveloped or abnormally positioned.
TSH receptor mutations is where the TSH receptors on the thyroid gland may be abnormal which means that TSH cannot properly stimulate the thyroid gland.
Dyshormonogenetic goiter where the thyroid gland is abnormally enlarged and underactive due to a genetic defect.

Overactive Thyroid Problems

Overactive thyroid problems is where there is excessive amounts of thyroid hormones circulating in the body. It is mainly due to overactivity of the the thyroid gland and is therefore known as hyperthyroidism but the preferred terms is thyrotoxicosis because the thyroid hormone levels are higher than normal. When the problem is with the thyroid gland itself then it is known as primary hyperthyroidism. Problems with the pituitary gland or hypothalamus that may lead to overproduction of thyroid hormones is known as secondary hyperthyroidism.

Graves disease

Graves disease is caused by the immune system where certain antibodies mimic TSH thereby over-stimulating the thyroid gland to produce excessive hormones. It is the most common type of hyperthyroidism.

Nodules

Several nodules on the thyroid gland can cause over-functioning and excessive thyroid hormone production. This is known as toxic multinodular goiter. However, a single or even multiple nodules may not always cause hyperthyroidism.

Benign tumor

A benign tumor of the thyroid gland can also produce thyroid hormones leading to high levels in the circulation. This is known as a toxic adenoma.

Iodine-induced hyperthyroidism

An excessive intake of iodine can cause overactivity of the thyroid gland. There is an excess of thyroid hormones produced and released leading to thyrotoxicosis.

Thyroiditis

Inflammation of the thyroid gland is known as thyroiditis and can cause overactivity of the gland. Not every type of thyroiditis affects thyroid function in this way. The inflamed thyroid gland may be painful or painless and the causes are not always identified.

Thyroid Problems Symptoms

The symptoms of thyroid problems may differ depending on whether it is hypothyroidism (low thyroid activity) or hyperthyroidism (high thyroid activity). In the early stages and with very slight dysfunction of thyroid activity the symptoms may be minor or not even noticeable. However, over time there will be clearly identifiable symptoms of thyroid dysfunction.

Low Thyroid Problems

The signs and symptoms of hypothyroidism includes :

Tiredness
Slowness
Muscle weakness
Weight gain
Sensitivity to cold
Pale skin
Dry skin and hair
Brittle fingernails
Thinning hair and hair loss
Depression
Heavy menstrual periods
Hoarse voice
Swollen face
High blood cholesterol
Muscle aches
Joint pains
Growth problems in children
Low body temperature
Constipation

High Thyroid Problems

The signs and symptoms of hyperthyroidism includes :

Tiredness
Goiter (neck swelling)
Rapid weight loss
Increased appetite
Excessive sweating
Sensitivity to heat
Muscle weakness
Insomnia
Frequent bowel movements
Tremor
Menstrual changes
Anxiety, irritability and excitability
Rapid heart rate
Irregular heart beat
Shortness of breath
Loss of libido
Hyperactivity
Eyelid retraction and protruding eyes (exopthalmos)

Picture of protruding eyes (exopthalmos) in Graves disease from Wikimedia Commons.

Thyroid Problems Diagnosis

Thyroid blood tests

The main blood tests for thyroid problems are collectively known as a thyroid profile. It monitors the following levels in the blood :

Thyroid hormones – T3 and T4
Thyroid-stimulating hormone (TSH)
Thyroid antibodies

The presence of thyroid antibodies is not usually tested routinely unless specifically requested.

Radioactive iodine uptake test

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A small dose of radioactive iodine is administered through the mouth. The thyroid glands usage of this iodine is then monitored. An overactive thyroid will use iodine more rapidly than a normal thyroid gland.

Thyroid scan

Harmless radioactive material known as contrast dye is injected into the bloodstream. It will eventually reach the thyroid gland and allow for the gland to be seen on a computer screen with a specially designed camera. This occurs without having to perform any surgery to reach the thyroid gland. Sometime this same scanning method can be used to view the thyroid gland after radioactive iodine has been consumed.

Thyroid Problems Treatment

There are certain medication and procedures to treat the thyroid gland itself or the some of the symptoms and complications of an overactive or underactive thyroid gland.

Synthetic thyroid hormone known as levothyroxine is used for hypothyroidism to replace the deficiency of natural thyroid hormones.
Anti-thyroid medication like propylthiouracil and methimazole block the thyroid gland from producing excess thyroid hormones in hyperthyroidism.
Radioactive iodine is used to shrink the thyroid gland in hyperthyroidism but can cause the thyroid gland to become underactive.
Thyroidectomy is surgery to remove part of the thyroid gland or the entire gland in hyperthyroidism.

Thyroid Problems Prevention

There is no specific way to prevent all types of thyroid problems. Iodine is needed for healthy thyroid functioning but too little iodine will cause an underactive thyroid while too much of iodine can lead to an overactive thyroid. Therefore iodine has to be consumed in moderate quantities. Fortunately there is small amounts of iodine in common household foods and condiments like salt. This means that a person will get a little iodine over a long period of time which is sufficient to maintain a healthy thyroid gland.

References :

http://www.nlm.nih.gov/medlineplus/thyroiddiseases.html
http://path.upmc.edu/cases/case425/dx.html
http://www.thyroid.org/patients/patient_brochures/iodine_deficiency.html