Hypothyroidism is usually associated with decreased production of hormone in the thyroid gland. Lack of iodine intake can also result in hypothyroidism in certain countries. Other causes of hypothyroidism include Hashimoto’s thyroiditis, radioactive iodine therapy, and medication induced and surgery. There are other rare causes of hypothyroidism that is beyond the scope of this site.
Goiter (endemic, multinodular)
Iron deficiency can result in a preventable endemic goiter. Mild to moderate iron deficiency still exists in many parts of the world. Multinodular goiter is described as diffusely enlarged thyroid gland that is often associated with nodularity that can be asymmetrical. With goiter a person can have normal thyroid levels or become hyperthyroid. Incidence of thyroid cancer in nodular goiter is reported between 5-9% and biopsy of suspicious nodules should be considered.
Thyroiditis is associated with inflammation or infection of the thyroid gland. Hashimoto’s thyroiditis is a major cause of hypothyroidism in the United States. This immunologic phenomenon is antibody mediated and results in altered thyroid hormone production and hypothyroidism. Acute thyroiditis is very rate and is the result of infection of upper airway and thyroid gland causing severe localized pain. The exact cause of subacute thyroiditis is not known but is associated with viral disease. It can also present as swelling of thyroid gland, pain, fever and fatigue. Treatment of thyroiditis is variable depending on the etiology of the disease.
Graves’ disease is one of the most common causes of hyperthyroidism. Other causes of hyperthyroidism include nodular goiter and thyroid adenomas and central nervous system disease. Clinical presentation of Graves’ is usually associated with neck mass, increased hypermetabolic state and exophthalmos in prolonged untreated situations. Increased heart rate, abnormal heart rate, sweating, weight loss, heat intolerance, hair loss and menstrual changes are some of manifestations of hyperthyroid state. The main treatment options for hyperthyroidism include anti-thyroid medications, radioactive iodine therapy and surgery. Antithyroid medications are the first line therapy in the management of patients with Graves' disease. Complete remission may be achieved with medical therapy in these patients.
The incidence of thyroid cancer in the United States is increasing but the etiology of this has been debated. Mortality from thyroid cancer remains low. In United states more than 60,000 new cases of thyroid cancer were predicted for 2014 compared to less than 40,000 in 2009.
Papillary thyroid cancer is the most common type of thyroid cancer making more than 90% of all thyroid cancers. It is more common in in women. It usually presents as a thyroid nodule or a slow growing neck mass with normal hormone levels. Lymph node metastasis is common in papillary thyroid cancer especially in younger patients and could be a presenting symptom. It is usually diagnosed by FNAB of thyroid or the lymph node. Papillary thyroid cancer can be multifocal. Distant metastasis is overall uncommon but the most common sites of metastases are lungs, bone, liver and brain. Overall survival in papillary thyroid cancer is excellent with >95% ten year survival rate.
Follicular thyroid cancer (FTC)
Incidence of follicular carcinoma in the United States is decreasing and it accounts for less than 10% of thyroid cancers. It is a disease of older population presenting often over the age of 50. Just like papillary, it is more common in women, but lymph node metastasis is uncommon at initial presentation. Follicular carcinoma usually presents as a solitary nodule and can spread through the circulatory system to distant sites. FNAB is not accurate in distinguishing benign follicular tumors and carcinoma unless metastatic disease is present.
Hurthle cell thyroid cancer
It is considered to be a subtype of follicular carcinoma and some studies suggest higher rate of recurrence. Prognosis is generally thought to be the same as FTC.
Medullary thyroid cancer
Medullary thyroid cancer (MTC) accounts for a small portion of thyroid cancers. It arises from the parafollicular or C-cells in the thyroid. These cells are located on the sides and upper aspect of thyroid and produce the hormone calcitonin. It functions to lower the blood levels of calcium. Most cases of MTC are not inherited; however, up to 25% can occur in the setting of familial MTC and Multiple Endocrine Neoplasia (MEN2A and MEN2B). MTC is associated with a genetic mutation in RET proto-oncogene. Patients with MTC will present with neck mass that may be associated with enlarged neck lymph nodes up to 20% of the cases. It usually presents at the 5th or 6th decade of life, but familial disease presents at younger age. Patients with MTC usually have elevated levels of calcitonin and/or carcinoembryonic antigen (CEA). High level of these hormones is associated with systemic symptoms such as diarrhea. In the setting of familial disease, genetic counselling and early treatment of children with certain mutations is essential for cure.
Anaplastic /Poorly differentiated
Anaplastic thyroid cancer accounts for less than 1% of all thyroid cancer in the United States. As with other types of thyroid cancer, it is more common in women and presents at older age. It usually presents as a rapidly growing neck mass in the setting of goiter and it can be painful. It may be associated with difficulty breathing and swallowing and voice changes. FNAB and core biopsy may be helpful in diagnosis. Overall prognosis of anaplastic thyroid cancer is poor. Multimodal therapy including surgery should be considered when possible.
Metastatic disease to the thyroid from other cancers such as kidneys, breast, lung and melanoma has been reported. FNAB may be helpful in diagnosing the type of tumor. In these cases treatment will depend on the extent of primary tumor. Lymphoma can also occur in the thyroid on rare cases. It accounts for about 1-5% of thyroid malignancies and presents as a rapidly growing mass. Core biopsy has a higher sensitivity compared to FNAB in the diagnosis of thyroid lymphoma.