Common hypothyroid symptoms include fatigue, low energy, weight gain, inability to tolerate the cold, slow heart rate, dry skin and constipation.

[5] Common hyperthyroid symptoms include irritability, anxiety, weight loss, fast heartbeat, inability to tolerate the heat, diarrhea, and enlargement of the thyroid.

Screening for thyroid disease in patients without symptoms is a debated topic although commonly practiced in the United States.

The main hyperthyroid conditions are: Certain medications can have the unintended side effect of affecting thyroid function.

It is not fully understood why this occurs, but it is thought to be partially genetic as these diseases tend to run in families.

[9] In one of the most common types, Graves' Disease, the body produces antibodies against the TSH receptor on thyroid cells.

In hyperthyroidism caused by Graves' Disease or toxic multinodular goiter, there is excess stimulation of the TSH receptor even when thyroid hormone levels are normal.

[23] During pregnancy, there is also an increase in estrogen which causes the mother to produce more thyroxine binding globulin, which is what carries most of the thyroid hormone in the blood.

If more information is needed after a clinical exam and lab tests, medical ultrasonography can help determine the nature of thyroid nodule(s).

There are some notable differences in typical benign vs. cancerous thyroid nodules that can particularly be detected by the high-frequency sound waves in an ultrasound scan.

For example, a nodule that is overactive ("hot") -- to the point of suppressing the activity of the rest of the gland—is usually a thyrotoxic adenoma, a surgically curable form of hyperthyroidism that is rarely malignant.

A normal quantitation of radioiodine uptake demonstrates that about 8-35% of the administered dose can be detected in the thyroid 24 hours later.

Overactivity or underactivity of the gland, as may occur with hyperthyroidism or hypothyroidism, is usually reflected in increased or decreased radioiodine uptake.

A medical biopsy refers to the obtaining of a tissue sample for examination under the microscope or other testing, usually to distinguish cancer from noncancerous conditions.

[citation needed] Fine needle aspiration has the advantage of being a brief, safe, outpatient procedure that is safer and less expensive than surgery and does not leave a visible scar.

The accuracy of the diagnosis depends on obtaining tissue from all of the suspicious areas of an abnormal thyroid gland.

The reliability of fine needle aspiration is increased when sampling can be guided by ultrasound, and over the last 15 years, this has become the preferred method for thyroid biopsy in North America.

[32][citation needed] Levothyroxine is a stereoisomer of thyroxine (T4) which is degraded much more slowly and can be administered once daily in patients with hypothyroidism.

Hyperthyroidism caused by Graves' disease may be treated with the thioamide drugs propylthiouracil, carbimazole or methimazole, or rarely with Lugol's solution.

A nodule or lobe of the thyroid is sometimes removed for biopsy or because of the presence of an autonomously functioning adenoma causing hyperthyroidism.

Consequently, individuals who have undergone a total thyroidectomy are typically placed on thyroid hormone replacement (e.g. levothyroxine) for the remainder of their lives.

Accidental laceration of either of the two or both recurrent laryngeal nerves may cause paralysis of the vocal cords and their associated muscles, changing the voice quality.

This is done either by withdrawal of thyroid hormone medication or injections of recombinant human TSH (Thyrogen),[31] released in the United States in 1999.

[37][38][39] An estimated one-third of the world's population currently lives in areas of low dietary iodine levels.

[40] In areas where iodine-deficiency is not found, the most common type of hypothyroidism is an autoimmune subtype called Hashimoto's thyroiditis, with a prevalence of 1-2%.

[40] As for hyperthyroidism, Graves' disease, another autoimmune condition, is the most common type with a prevalence of 0.5% in males and 3% in females.