There are several thyroid diseases with different causes.
The thyroid is a gland located at the base of the neck that produces thyroid hormones – thyroxine (T4) and triiodiothyronine (T3) – which play a key role in the proper functioning of our body. However, the gland does not always work properly, which can result in different types of thyroid problems, such as hypothyroidism or hyperthyroidism, goitre, nodules, thyroiditis or cancer.
Hypothyroidism
Hypothyroidism is the most common thyroid disease and occurs when the gland does not produce adequate quantities of thyroid hormones. The initial stage of the disease, which is usually very slow, may involve the development of a form known as subclinical hypothyroidism, during which only the TSH values increase, while the other thyroid hormone levels remain normal, with few or no symptoms. However, the values of these hormones subsequently decrease and symptoms including fatigue, increased sensitivity to cold, weight gain or constipation generally ensue. If hypothyroidism is not diagnosed and treated appropriately, in the long run it can cause various problems, such as obesity, irregular periods, infertility, hypercholesterolaemia and heart disease.
The causes of hypothyroidism
The most common cause of hypothyroidism is Hashimoto’s thyroiditis, an autoimmune disease in which the patient’s immune system attacks and damages his/her own thyroid, preventing it from being able to produce adequate quantities of thyroid hormones. However, hypothyroidism can also occur following the surgical removal of the thyroid (thyroidectomy) or as a consequence of treatment with the radioactive iodine used to treat hyperthyroidism or thyroid tumours, or as a result of radiation to the head and neck, usually administered as radiotherapy to treat cancer, or following the use of certain medicines, such as amiodarone or lithium.
Hyperthyroidism
When the thyroid produces and releases into the bloodstream excessive quantities of thyroid hormones we are faced with a condition known as hyperthyroidism, which can cause different symptoms such as anxiety, hyperactivity, nervousness, sudden and excessive weight loss, tachycardia, arrhythmia or palpitations, intense sweating, irregular periods, intolerance towards heat or intestinal disorders.
What are the causes of hyperthyroidism?
The most common cause of hyperthyroidism is Graves’ disease, an autoimmune disease that affects individuals of all ages and is usually characterised by the presence of a goitre (enlargement of the thyroid) and/or eye symptoms like swelling around the eyes, increased tear production, irritation and increased sensitivity to light, as well as two characteristic symptoms, namely bulging eyes (protrusion of the eyeballs or exophthalmos) and double vision (diplopia).
In addition to this, there can be other causes, such as certain types of nodules which start producing and releasing into the bloodstream excess thyroid hormones (toxic adenoma, toxic multinodular goitre and Plummer disease) or thyroiditis (an inflammation of the gland that causes large quantities of thyroid hormones to be released into the bloodstream). The onset of hyperthyroidism can also be caused by certain drugs, such as amiodarone (thyrotoxicosis), which is used to control heartbeat abnormalities.
Goitre
A goitre is an enlargement of the thyroid and the symptoms it causes depend on the size of the gland and whether there are any changes in thyroid function. As a matter of fact, goitres are referred to as toxic when they are associated with hyperthyroidism or nontoxic when they occur without any excessive or decreased thyroid hormone production.
The enlargement of the thyroid can either involve the whole gland equally, in which case it is known as a diffuse goitre, or it can be asymmetric due to the presence of solid or fluid-filled nodules, in which case it is known as a nodular goitre.
The causes of goitres
Although most goitres are the result of iodine deficiency, they can also be caused by autoimmune thyroid diseases such as Hashimoto’s thyroiditis, in which the thyroid increases in volume in order to maintain adequate thyroid hormone production, or, as in the case of Graves’ disease, be the consequence of excessive hormone production. However, goitres can also occur as a result of other causes, for example the use of certain medicines (antithyroid drugs, lithium) or eating large amounts of foods referred to as goitrogenic, in other words foods containing substances that can interfere with iodine metabolism, which are generally found in cruciferous vegetables (cabbage, turnips, broccoli and cauliflower).
Nodules
Thyroid nodules are small solid or fluid-filled (cysts) lumps of varying sizes that develop inside the thyroid. They are almost always benign and are often discovered completely incidentally. Their presence does not affect thyroid function and in most cases they do not cause any symptoms (occasionally they may lead to a feeling of compression or pain at the base of the neck), but they must be examined by a doctor in order to rule out tumours or possible future dysfunctions.
Causes
Although nodules are very common in the population, the causes of thyroid nodules are still unclear; however, a lack of iodine in the diet and a familiarity for this condition seem to be the most likely culprits.
Thyroiditis
Thyroiditis is an inflammation of the thyroid gland that causes changes in the amount of thyroid hormones produced. There are different types of thyroiditis, each of which has specific causes and symptoms.
Causes
There are different forms of thyroiditis caused by different factors: Hashimoto’s thyroiditis (a chronic autoimmune inflammation caused by an excessive production of antithyroid antibodies by the immune system that causes hypothyroidism), post-partum thyroiditis (a form of autoimmune thyroiditis that occurs after giving birth and can cause temporary hyperthyroidism followed by hypothyroidism), subacute or De Quervain’s thyroiditis (characterised by an acute and painful inflammation of the thyroid caused by viral infections, which can result in temporary hyperthyroidism that can, in some cases, be followed by a phase of hypothyroidism), acute thyroiditis (caused by bacterial infection), a rare form known as Riedel thyroiditis (a chronic inflammation of the thyroid in which the gland becomes fibrotic and can cause difficulties breathing and swallowing) and actinic or iatrogenic thyroiditis (in which the inflammation is caused by the use of medicines that are detrimental to the thyroid, such as amiodarone, or by radiotherapy for neck or mediastinal tumours or the treatment of hyperthyroidism).
Tumours
Thyroid tumours develop as a result of the uncontrolled growth of the cells inside the thyroid gland. There are different kinds, most of which are benign and do not cause any symptoms; however, in rare cases they can be malignant and cause symptoms such as nodules or lumps in the throat, difficulties swallowing or breathing and voice changes.
The treatment of thyroid tumours depends on the nature of the tumour (benign or malignant) and its size: benign tumours can simply be monitored with regular check-ups, whereas malignant tumours require surgery to remove the entire gland (thyroidectomy), possibly followed by treatment with radioactive iodine or chemotherapy.
Causes of thyroid tumours
The main causes that can result in the development of a tumour are exposure to ionising radiation (e.g. radiotherapy or exposure to radioactive material), a goitre (which in some cases results in a predisposition for malignant transformation of the cells), recurrence of a previous thyroid tumour, iodine deficiency or hereditary genetic diseases (such as medullary thyroid cancer, multiple endocrine neoplasia and familial adenomatous polyposis).
REFERENCES
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- Harper, M.B., Mayeaux, E. (2005). Thyroid Disease. In: Taylor, R.B., David, A.K., Fields, S.A., Phillips, D.M., Scherger, J.E. (eds) Taylor’s Diagnostic and Therapeutic Challenges. Springer, New York, NY. https://doi.org/10.1007/0-387-27287-9_14
The information provided on the website www.feelthyroid.com is not intended as a substitute for doctor-patient relations or specialist consultations. It is advisable to always consult your doctor and/or a specialist regarding the information and guidance provided.