The thyroid gland uses iodine to make the thyroid hormone. This hormone affects almost every cell in the body. Thyroid disease can, therefore, have wide-reaching effects. Thyroid disease can be malignant or it can be benign. It can also cause the secretion of low levels of the thyroid hormone or produce high levels.
Hypothyroidism
Hypothyroidism means low levels of the thyroid hormone. Worldwide, the most common cause of hypothyroidism is the lack of iodine. In America where there is no iodine deficiency, Hashimoto's thyroiditis is the most common cause, according to Paul Fitzgerald, M.D., Clinical Professor of Medicine at the University of California in "Current Medical Diagnosis & Treatment." Hashimoto's is an autoimmune disease. The immune system attacks the thyroid gland, which makes and releases the thyroid hormone, instead of only attacking foreign substances. Abnormalities in the thyroid gland or in the anterior pituitary gland can also cause hypothyroidism. The anterior pituitary gland in the brain secretes the thyroid stimulating hormone (TSH). This tells the thyroid gland to make thyroid hormone. If the anterior pituitary secretes low levels of TSH, this can lead to hypothyroidism.
Hyperthyroidism
The primary reason for hyperthyroidism is Graves' disease, as Jerome Hershman, M.D., Distinguished Professor of Medicine at the David Geffen School of Medicine writes in "The Merck Manual for Healthcare Professionals." Like Hashimoto's thyroiditis, Graves' disease is an autoimmune disease. In Hashimoto's, antibodies destroy the thyroid gland. In Graves' disease, the antibodies stimulate the gland and cause it to make abnormally high levels of the thyroid hormone. Other reasons for hyperthyroidism include too much secretion of TSH by the anterior pituitary, Plummer's disease, lymphocytic thyroiditis and struma ovarii. In Plummer's disease, people have many thyroid nodules. Lymphocytic thyroiditis can occur after giving birth. Struma ovarii is an ovarian tumor that has thyroid tissue.
Thyroid Nodule
Thyroid nodules are a very common type of thyroid disease. In "Current Medical Diagnosis & Treatment," Dr. Fitzgerald writes that physicians detect approximately 275,000 nodules every year. The risk of having such a nodule increases with age, and women have these nodules four times more than men. The overwhelming majority are benign. Most nodules do not cause either hypothyroidism or hyperthyroidism, but some do cause one or the other. The risk factors for having a malignant nodule include having some other type of malignancy, having a family history of thyroid cancer or having a history of radiation to the head or neck.
Thyroid Cancer
There are four main kinds of thyroid cancer, according to Dr. Hershman in "The Merck Manual for Healthcare Professionals." Anaplastic carcinoma is primarily seen in the elderly. It is painful and grows very fast. Follicular carcinoma is also mainly seen in the elderly population. It spreads through the bloodstream to the bones and lungs. People with medullary carcinoma may have this thyroid cancer along with cancers in other areas of the body. Papillary carcinoma is the most common type of thyroid cancer. It slowly grows and spreads through the lymphatics.
Diagnosis
William Hueston, M.D. of the Medical University of South Carolina, writes in "Current Diagnosis & Treatment in Family Medicine" about the several tools available to physicians to diagnose thyroid disease. Thyroid function tests check the levels of TSH and thyroid hormones. People can take tests to check for any antibodies present in Hashimoto's and Graves' diseases. An ultrasound can check for abnormalities, as can a radioactive iodine scan and fine-needle aspiration.
References
- "Current Diagnosis & Treatment in Family Medicine"; Jeannette South-Paul, M.D., Samuel Matheny, M.D., Evelyn Lewis, M.D.; 2008
- "Current Medical Diagnosis & Treatment 2010"; Stephen McPhee, M.D., Maxine Papadakis, M.D.; 2010
- The Merck Manual for Healthcare Professionals: Hyperthyroidism
- The Merck Manual for Healthcare Professionals: Thyroid Cancers
