Goiter is defined as an abnormal enlargement of the thyroid gland causing a swelling in the neck. It, however, does not necessarily mean that the thyroid is malfunctioning. The thyroid gland can be absolutely normal as in euthyroidism.
But, a goiter can simultaneously occur in a thyroid gland that is producing too much of thyroid hormones (T3 and T4) as in hyperthyroidism or in one that is producing too little of the hormones as in hypothyroidism.
Therefore, a goiter occurs due to a cause independent of any thyroid condition.
The goiter (enlargement) is more common in women than in men and it may be diffuse or the thyroid may become nodular.
Most of the goiters are harmless and are curable except the thyroid nodules that become malignant and life-threatening.
Malignant thyroid nodules can be treated and even those which have spread to the lymph glands are rarely fatal.
What causes Thyroid Goiter?
There are various reasons that can cause enlargement of the thyroid.
Deficiency of iodine in the diet
The most common cause of goiter worldwide primarily is lack of iodine intake due to dietary deficiency. The cells of the thyroid are the only cells in the body that take up iodine from the blood to make thyroid hormones. The blood gets it from the food that we eat.
So, lack of iodine in the food deprives the thyroid of this essential mineral leading to less thyroid hormones being produced.
The pituitary gland senses this and secretes the thyroid stimulating hormone (TSH), which stimulates the thyroid to produce more of its hormone. This overworks the thyroid because it cannot produce enough hormones due to lack of iodine. It, therefore, grows in size and forms a goiter.
This cause is more common in underdeveloped countries where the awareness of the iodine importance is still absent.
Hashimoto’s Thyroiditis or Hashimoto’s disease is a condition where the body’s own immune system attacks the thyroid. As the thyroid gland gets gradually inflamed and damaged, it is unable to produce enough thyroid hormones. This can lead to hypothyroidism.
Due to low blood hormone levels, the pituitary secretes more of TSH sending the thyroid tissue into overdrive. It causes the thyroid tissue to grow, which produces the goiter. This condition is the most common cause of hypothyroidism in the United States.
Thyroiditis is a painful condition with tenderness present.
Graves’ disease also known as toxic diffuse goiter is another autoimmune disease that affects the thyroid and causes the entire gland to grow.
The immune system produces a protein, called thyroid stimulating immunoglobulin (TSI), which stimulates the thyroid to grow in size and produce more hormones. This can lead to hyperthyroidism and goiter.
As a result of more thyroid hormones in the blood, the pituitary stops secreting TSH, in spite of which the thyroid continues to grow and make more hormones.
The exact cause of Graves’ disease is not known but it is believed to be due to genetic and environmental factors.
Toxic multinodular goiter
Multiple nodules can develop in the thyroid and form a nodular goiter. Why the nodules develop is still not clear.
There may be a single large nodule or multiple nodules. Multinodular goiter can be a toxic multinodular goiter, making too much thyroid hormone and causing hyperthyroidism or non-toxic where there is no overproduction of thyroid hormones
It is not known what causes multinodular goiters in most cases, but iodine deficiency and genetic factors are believed to part of the etiology.
This is the most common disorder of the thyroid leading to hyperthyroidism.
The nodules are functionally autonomous and do not require stimulation from thyroid stimulating hormone (TSH) to produce thyroid hormones.
Most of the nodules are benign but about 10 to 15 % can become malignant.
Cancer of the thyroid causes the thyroid to enlarge and presents as a lump in the neck. It can be primary or a secondary from a primary cancer source somewhere else in the body.
It is not common and females are more likely to suffer from thyroid cancer at a ratio of 3:1.
Symptoms of goiter
Goiter presents as a visible swelling at the base of the neck anteriorly. Symptoms of goiter are mainly due to the enlarged thyroid pressing on the neighboring structures in the neck.
- Pressure on the trachea (windpipe) by the enlarged thyroid results in difficulty in breathing (dyspnea), cough and waking up at night due to sudden choking. Change in the voice is also seen.
- Pressure on the esophagus by the enlarged thyroid gives rise to difficulty in swallowing (dysphagia), and a feeling of something being stuck in the throat. The esophagus is situated behind the trachea and therefore these symptoms are felt later when the enlargement has fairly progressed.
- Pressure on the neighboring blood vessels by the enlarged thyroid causes them to dilate and are seen as engorged blood vessels in the neck.
Diagnosis of Goiter
The doctor easily diagnoses the goiter by palpating your neck and feeling the lump (with or without nodules) and observing it by asking you to swallow.
Besides the appearance of an enlarged thyroid in the neck, blood tests for goiter are done to determine what has caused the goiter.
Thyroid function test through blood analysis will show levels of thyroid hormones (T3 and T4) and levels of TSH.
If the thyroid is overactive, it will show increased levels of T3 and T4 and low levels of TSH.
In a goiter with an underactive thyroid, the reverse will be the case.
Modern measurement of thyroid hormones is done by a new technique, radioimmunoassay (RIA), which is fairly accurate.
- Measurement of Serum Thyroid Hormone T4 by RIA
- Measurement of Serum Thyroid Hormone T3 by RIA
- Measurement of Pituitary Production of TSH: Pituitary production of TSH is calculated by a method called as IRMA (immunoradiometric assay). Usually, low levels (less than 5 units) of TSH are enough to maintain the normal thyroid gland function.
When the thyroid function suffers as in early hypothyroidism, the TSH levels become elevated even though the T3 and T4 may still be normal.
This is due to the pituitary gland’s response to a fall in thyroid hormones and indicates dysfunctioning of the thyroid gland.
However, the failure of TSH to rise when thyroid hormones level in blood are low indicates impaired pituitary function.
Other tests to diagnose the cause of goiter are:
- Radioactive iodine scan is done to measure how much iodine is taken up by the thyroid gland (RAI uptake). Hypothyroid patients usually take up less of iodine and hyperthyroid patients take up too much of it. The production of thyroid hormones is dependent upon proper absorption of iodine.
- Thyroid ultrasound is done to identify if the nodule is solid or filled with fluid as in a cyst.
- A fine needle aspiration biopsy is done to differentiate a malignant nodule from a benign one.
Treatment of Goiter
Treatment of goiter involves treating the cause of the goiter.
If low iodine intake has caused the goiter, iodine supplements and thyroid hormones will suffice. However, the goiter will reduce in size, but, usually does not resolve completely.
Thyroid hormone supplement
If Hashimoto’s Thyroiditis with hypothyroidism is the cause, you will be given thyroid hormone supplement as a daily pill. This will bring back your normal hormone levels but the goiter does not completely go away.
Treatment of Graves’ disease with radioactive iodine usually resolves the goiter.
Thyroid Goiter surgery
Multinodular goiters with normal levels of thyroid hormones are left alone. However, if they press on the trachea or the esophagus and cause symptoms, then surgical removal is the only option.
Another indication for thyroid surgery is a malignant nodular goiter where a thyroid lobectomy or hemithyroidectomy may be necessary.
If you have been diagnosed with goiter, regular monitoring is necessary. A goiter can correct itself over time on its own or it could be due to a cause as explained above. This will help to avoid treatment and its side effects till symptoms manifest.