The thyroid gland is an endocrine organ located in the neck that synthesizes and releases T3 and T4 (thyroid hormones). These hormones play a major role in body metabolism and affect a wide range of body systems. When a problem with the thyroid gland begins to develop, often systemic symptoms can develop.
Hyperthyroidism
Hyperthyroid is overactivity of the thyroid gland. Clinical features of hyperthyroidism include nervousness, irritability, tremor, excessive sweating, heat intolerance, diarrhea, weight loss, palpitations, muscle weakness and increased heart rate. This is due to increased amount of circulating thyroid hormones and common causes include Graves' disease (the most common cause), Plummer's disease (also known as multinodular toxic goiter) and exogenous administration of levothyroxine hormone. Graves' disease hyperthyroidism has the unique symptoms of having eyeballs that are protruding in addition to characteristic pitting skin changes over the shins that can help distinguish it from the other types.
Hypothyroidism
Hypothyroid occurs when there is a deficiency of thyroid hormone in the blood circulation. Often, it is asymptomatic and diagnosis is made incidentally on laboratory analysis. Symptoms include fatigue, weakness, heavy menstrual periods, cold intolerance, constipation, inability to concentrate, depression, dry skin, hoarseness, decreased heart rate and diminished hearing. Symptoms are due to decreased amounts of circulating thyroid hormones and causes include Hashimoto's disease (most common cause), problems with the pituitary gland in the brain (that normally regulates thyroid function) and from iatrogenic causes. Iatrogenic refers to medical interventions such as surgery on the thyroid gland or medications that have an anti-thyroid effect.
Subacute Viral Thyroiditis
Viral thyroiditis, also known as subacute granulomatous thyroiditis, is usually caused by a preceding viral illness. It results in a painful, tender thyroid gland with an early phase composed of fever and flu-like symptoms. Often, it can cause transient hyperthyroid symptoms due to leakage of thyroid hormone from the inflamed gland. As the hormones are depleted, a hypothyroid state can ensue, with recovery of thyroid function usually following within the next year.
Painless Thyroiditis
This is also known as subacute lymphocytic thyroiditis. It is characterized by a transient hyperthyroid phase, which is followed by a hypothyroid phase. It is similar to subacute viral thyroiditis and is differentiated only by the lack of a painful thyroid gland.
Riedel's Thyroiditis
This is also known as fibrous thyroiditis, which describes the disease quite aptly. It is characterized by fibrous tissue replacing the thyroid, which results in an abnormally firm gland that can necessitate surgery if complications occur. Often, the patients are hypothyroid, which necessitates thyroid hormone therapy.
Cancer
The most feared thyroid problem is the occurrence of cancer. Risk factors for cancer development in the thyroid gland include radiation of the head and neck, and genetic predisposition (such as Gardner's syndrome or MEN type II syndrome). There are a variety of different thyroid cancer types such as papillary carcinoma (accounts for the majority of thyroid cancers), follicular carcinoma, medullary carcinoma and anaplastic carcinoma (has the worst prognosis). Patients often have normal thyroid hormone levels. Therapy includes surgery, chemotherapy and radioactive iodine administration.
References
- "Step-Up to Medicine, 2nd Edition"; Agabegi; 2008
- "Williams Textbook of Endocrinology, 11th Edition"; Kronenberg; 2008
