Thyroid Glossary

Adenoma

A benign growth in the thyroid. A toxic adenoma produces excess hormone independently of the body’s control.

Alcohol ablation

A minimally invasive treatment for recurrent benign thyroid cysts in which alcohol is injected to stop the cyst refilling.

Anti-thyroglobulin antibodies

Antibodies against thyroglobulin, a protein the thyroid uses to store hormone. They are a marker of autoimmune thyroid disease and can interfere with thyroglobulin testing in cancer follow-up.

Anti-TPO antibodies

Antibodies against thyroid peroxidase, a marker of autoimmune thyroid disease such as Hashimoto’s.

Antithyroid drugs

Medicines such as carbimazole, methimazole and propylthiouracil that reduce thyroid hormone production in an overactive thyroid.

Bethesda system

A standardised reporting system for thyroid fine-needle aspiration results, grading the likelihood of cancer and guiding the next step.

Bradycardia

A slow heart rate, which can occur in hypothyroidism as well as in athletes, medication use and heart conduction problems.

Calcitonin

A hormone produced by the thyroid’s C-cells. It is used as a tumour marker for medullary thyroid cancer.

Carbimazole

An antithyroid medicine that reduces thyroid hormone production. It is converted to methimazole in the body.

Central hypothyroidism

An underactive thyroid caused by a pituitary or hypothalamic problem rather than by the thyroid gland itself.

Checkpoint inhibitors

Cancer immunotherapy medicines that unleash the immune system. They commonly cause thyroid inflammation and hypothyroidism.

Colloid nodule

A common benign thyroid nodule composed mainly of colloid, the storage material of the thyroid.

De Quervain thyroiditis

Another name for subacute thyroiditis — a painful, temporary inflammation of the thyroid, often after a viral illness.

DXA (bone density scan)

A low-radiation scan that measures bone mineral density. It may be used after prolonged hyperthyroidism or long-term TSH suppression.

Ectopic thyroid

Thyroid tissue located outside its normal position, often along the path from the tongue to the neck. It is a cause of congenital hypothyroidism.

Euthyroid

Having normal thyroid function — thyroid hormone levels within the reference range.

Exophthalmos

Bulging of the eye, a feature of thyroid eye disease associated with Graves’ disease.

FNAC (Fine Needle Aspiration Cytology)

A biopsy procedure using a thin needle to sample cells from a thyroid nodule for cancer evaluation.

Follicular thyroid cancer

A differentiated thyroid cancer arising from the hormone-producing cells, which can spread through the bloodstream.

Free T3 (FT3)

The unbound, active form of triiodothyronine — a thyroid hormone more potent than T4. Useful in detecting T3-predominant hyperthyroidism.

Free T4 (FT4)

The unbound, biologically active form of thyroxine — the main hormone produced by the thyroid. Measured alongside TSH to confirm thyroid status.

Goitre

An enlarged thyroid gland, which can occur with both hypothyroidism and hyperthyroidism.

Goitrogen

A substance in some foods, such as cruciferous vegetables, that can interfere with iodine use. It is not a concern in normal cooked amounts with adequate iodine.

Graves’ disease

An autoimmune cause of hyperthyroidism where antibodies stimulate the thyroid to overproduce hormone.

Hashimoto’s thyroiditis

An autoimmune condition where the immune system attacks the thyroid, most commonly causing hypothyroidism.

Hashitoxicosis

A temporary overactive phase in a person with Hashimoto’s thyroiditis, often caused by hormone leakage from inflammation.

Hurthle cell

A type of thyroid cell that can appear in benign and malignant nodules. Hurthle cell carcinoma is a less common thyroid cancer.

Hyperthyroidism

An overactive thyroid producing too much hormone. Common symptoms include weight loss, palpitations, anxiety and heat intolerance.

Hypoparathyroidism

Low parathyroid hormone causing low blood calcium. It can be temporary or permanent after thyroid surgery.

Hypothyroidism

An underactive thyroid producing too little hormone. Common symptoms include fatigue, weight gain, cold intolerance and constipation.

Iodine

An essential nutrient the thyroid uses to make hormone. Both deficiency and excess can cause thyroid disease.

Iodine deficiency

Insufficient iodine intake, which can cause goitre and hypothyroidism and, in pregnancy, affect the baby’s development.

Isthmus

The bridge of thyroid tissue connecting the two lobes of the gland, lying in front of the windpipe.

Levothyroxine

A synthetic form of T4 hormone used to treat hypothyroidism. Taken once daily, usually on an empty stomach.

Liothyronine

A synthetic form of T3 hormone, sometimes used in combination with levothyroxine in selected patients.

Lobectomy

Surgical removal of one lobe of the thyroid, leaving the other lobe in place.

Medullary thyroid cancer

A thyroid cancer arising from the calcitonin-producing C-cells. It can be inherited as part of MEN2.

MEN2

Multiple endocrine neoplasia type 2 — an inherited syndrome causing medullary thyroid cancer, adrenal tumours and sometimes parathyroid disease.

Methimazole

An antithyroid medicine that reduces thyroid hormone production. It is closely related to carbimazole.

Myxoedema

Tissue swelling caused by severe hypothyroidism, producing puffy skin, especially around the face and legs.

Myxoedema coma

A rare, life-threatening complication of severe untreated hypothyroidism requiring emergency treatment.

Papillary thyroid cancer

The most common thyroid cancer, arising from the hormone-producing cells and often spreading to neck lymph nodes.

Parathyroid glands

Four small glands behind the thyroid that control calcium balance. They can be disturbed during thyroid surgery.

Postpartum thyroiditis

A temporary inflammation of the thyroid occurring in the months after childbirth, often causing a thyrotoxic phase followed by a hypothyroid phase.

Propylthiouracil

An antithyroid medicine, often preferred in the first trimester of pregnancy.

Radioactive iodine (RAI)

A treatment for hyperthyroidism and thyroid cancer that uses radioactive iodine to destroy overactive or cancerous thyroid tissue.

Radioactive iodine uptake test

A test that measures how much iodine the thyroid takes up, helping distinguish Graves’ disease from thyroiditis.

Recurrent laryngeal nerve

The nerve that controls the vocal cords and runs close to the thyroid. It can be affected by thyroid surgery or compression.

Reverse T3

An inactive form of thyroid hormone produced when T4 is diverted away from making active T3, often during illness or stress.

Selenium

A trace mineral involved in thyroid hormone metabolism. Supplementation should be discussed with a clinician.

Silent thyroiditis

A painless inflammation of the thyroid that causes a temporary thyrotoxic phase followed by a hypothyroid phase.

Subacute thyroiditis

A painful, temporary inflammation of the thyroid, often following a viral illness and passing through thyrotoxic and hypothyroid phases.

Subclinical hyperthyroidism

Low TSH with normal free T4/T3 — mild thyroid overactivity that may need monitoring or treatment depending on age and risk factors.

Subclinical hypothyroidism

Elevated TSH with normal free T4 — mild thyroid underactivity that may not need immediate treatment but should be monitored.

Suppurative thyroiditis

A rare bacterial infection of the thyroid causing fever and a painful neck swelling.

Thyroglobulin

A protein the thyroid uses to store hormone. It is also used as a tumour marker after treatment for differentiated thyroid cancer.

Thyroid hormone resistance

A rare genetic condition in which tissues respond poorly to thyroid hormone, often producing high hormone levels with normal or high TSH.

Thyroid nodule

A lump or growth in the thyroid gland. Most are benign, but evaluation is needed to exclude cancer.

Thyroid peroxidase

An enzyme the thyroid uses to make hormone. Anti-TPO antibodies target it in autoimmune thyroid disease.

Thyroid storm

A rare, life-threatening complication of severe hyperthyroidism requiring emergency treatment.

Thyroid ultrasound

An imaging test that evaluates thyroid structure, nodules and surrounding tissues without radiation.

Thyroidectomy

Surgical removal of all or part of the thyroid gland, used for cancer, large goitres or compressive symptoms.

Thyrotoxicosis

The clinical state of having excess thyroid hormone, whether from an overactive thyroid or from hormone leaking out of an inflamed gland.

Thyroxine-binding globulin

The main protein that carries thyroid hormone in the blood. Its levels change in pregnancy and with some medicines.

TIRADS

A thyroid ultrasound risk-scoring system that categorises nodules from benign-appearing to highly suspicious.

Total thyroidectomy

Surgical removal of the entire thyroid gland, requiring lifelong thyroid hormone replacement.

TRAb (TSH Receptor Antibodies)

Antibodies that stimulate the thyroid in Graves’ disease, used to confirm the diagnosis.

TSH (Thyroid-Stimulating Hormone)

A hormone produced by the pituitary gland that signals the thyroid to produce thyroid hormones. It is the first-line screening test for thyroid function.

TSH suppression

Deliberately keeping TSH low with thyroid hormone, used in selected thyroid cancer patients to reduce stimulation of cancer cells.

Vocal cord paralysis

Loss of movement of a vocal cord, which can cause hoarseness. It may occur after thyroid surgery or from nerve compression.

This glossary is for educational purposes only and does not constitute medical advice. Read our editorial policy.