This page compiles our content related to thyroid dysfunction. For further information on diagnosis and treatment, follow the links below to our full BMJ Best Practice topics on the relevant conditions and symptoms.
The thyroid gland produces, stores, and secretes thyroxine (T4) and triiodothyronine (T3) through a negative feedback process involving the hypothalamus and pituitary gland. Thyroid dysfunction can result when any part of this process is affected, and is usually characterized by the presence of high or low levels of thyroid-stimulating hormone (TSH, secreted by the pituitary gland) and free thyroid hormones. Causes of thyroid disorders include autoimmunity (e.g., Graves disease), infections (e.g., postviral inflammation), other systemic medical conditions, medications (e.g., lithium, amiodarone), nutritional excesses or deficiencies (e.g., of iodine), tumors (thyroid, or rarely pituitary), trauma, or pregnancy.
Thyroid function tests (TFTs) are the most commonly used endocrine test. A serum TSH assay is the test of choice to screen for thyroid function disorders in the absence of hypothalamic or a pituitary pathology. Suppressed or elevated TSH confirms presence of thyroid dysfunction but not its cause. Free T4 assay is the test of choice to evaluate an abnormal TSH level. Further testing (e.g, radioactive iodine uptake) may be used subsequently to clarify etiologies in some cases.
Graves disease is an autoimmune thyroid disease and is the most common form of hyperthyroidism in countries with sufficient iodine intake. Hyperthyroidism is caused by TSH receptor antibodies (TRAb). Extrathyroidal manifestations include orbitopathy, pretibial myxoedema (thyroid dermopathy), or acropachy, which do not occur with other causes of hyperthyroidism. Diagnosis is mostly clinical and is usually confirmed by laboratory evidence of thyroid dysfunction, most commonly hyperthyroidism. 
A toxic multinodular goiter (MNG; also known as Plummer disease) contains multiple autonomously functioning nodules, resulting in hyperthyroidism. Nodules function independently of TSH and are almost always benign. However, nonfunctioning thyroid nodules in the same goiter may be malignant. Worldwide, iodine deficiency is the most common cause of nodular goiter.
An autonomously functioning thyroid nodule that causes hyperthyroidism. Typically a single large thyroid nodule accompanied by clinical and biochemical hyperthyroidism. These nodules are almost always benign. Worldwide, iodine deficiency is the most common cause of nodular goiter.
Autoimmune-mediated inflammation of the thyroid gland with release of thyroid hormone, resulting in transient hyperthyroidism, frequently followed by a hypothyroid phase before recovery of normal thyroid function. Occurs sporadically, postnatally, or during immunomodulatory or lithium therapy. Some patients progress to permanent hypothyroidism early, others years or decades later.
Inflammation of the thyroid characterized by a triphasic course of transient thyrotoxicosis, followed by hypothyroidism, followed by return to euthyroidism. The initial thyrotoxic phase is associated with thyroid pain, high serum thyroid hormone levels with a low radioiodine uptake, elevated erythrocyte sedimentation rate, elevated C-reactive protein, and a systemic illness similar to influenza, with fever, myalgia, and malaise.
Clinical state resulting from underproduction of T4 and T3. Patients with primary hypothyroidism usually present with non-specific symptoms of weakness, lethargy, depression, and mild weight gain. Low free T4 with an elevated TSH is diagnostic of primary hypothyroidism. Autoimmune thyroiditis (Hashimoto disease) is the most common cause of primary hypothyroidism in iodine-sufficient areas.
The result of anterior pituitary or hypothalamic hypofunction. It may be the result of congenital, neoplastic, inflammatory, infiltrative, traumatic, or iatrogenic etiologies. Pituitary mass lesions, especially pituitary adenomas, are the most common cause.
Most commonly presents as an asymptomatic thyroid nodule detected by palpation or ultrasound in a woman in her 30s or 40s. Four types account for more than 98% of thyroid malignancies: papillary, follicular, anaplastic, and medullary. The most important diagnostic test is fine-needle aspiration.
Thyroid parenchymal expansion can result from diffuse enlargement or infiltration of the thyroid gland, or from the presence of one or more thyroid nodules. Enlargement of other nearby anatomical structures, such as the parathyroid glands or regional lymph nodes, as well as branchial cleft and thyroglossal duct cysts, may sometimes be confused with thyroid nodules.
Ultrasonography is the initial test of choice for evaluating the structure and anatomic location of a neck mass.
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