Thyroid disease

Thyroid disease is common and treatment is highly effective. Dr Louise Johnson tells us more.

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What is the thyroid?

The thyroid is a small gland, measuring about 5cm, that lies under the Adam’s apple in the neck. The two halves (lobes) of the gland are connected in the middle (called the isthmus), giving it the shape of a bow tie. Normally the thyroid gland can’t be seen and can barely be felt.

The thyroid gland secretes thyroid hormones, which control the speed at which the body’s chemical functions proceed (metabolic rate). The thyroid hormone influences the metabolic rate in two ways:

• By stimulating almost every tissue in the body to produce proteins.
• By increasing the amount of oxygen that cells use.

Thyroid hormones affect many vital body functions, such as the heart rate, the rate at which calories are burned, skin maintenance, growth, heat production, fertility and digestion.

Thyroid hormones

There are two thyroid hormones:

• T4 (Thyroxine)
• T3 (Triiodothyronine)

T4, the major hormone produced by the thyroid gland, has only a slight effect, if any, on speeding up the body’s metabolic rate. Instead T4 is converted into T3, the more active hormone.

The conversion of T4 to T3 occurs in the liver and other tissues. Most of T4 and T3 in the bloodstream is carried bound to a protein called thyroxine-binding globulin. Only a little of T4 and T3 is circulating in the blood. However, it’s the free hormone that is active.

To produce the thyroid hormones, the thyroid gland needs iodine, an element contained in food and water. The thyroid gland traps the iodine and processes it into thyroid hormones. As the thyroid hormones are used, some of the iodine contained in the hormones is released, returns to the thyroid gland, and is recycled to produce more thyroid hormones.

The body has a complex mechanism for adjusting the level of thyroid hormones. First the hypothalamus, located above the pituitary gland in the brain, secretes thyrotropin-releasing hormone, which causes the pituitary gland to produce thyroid-stimulating hormone (TSH).

TSH stimulates the thyroid to produce hormones. The pituitary gland slows or speeds the release of TSH, depending on whether the level of thyroid hormones circulating in the blood are too low or too high.

Diagnostic tests for thyroid disease

1. The neck of a person is examined to feel whether the thyroid gland is palpable.
2. Blood tests are done measuring T4, T3 and TSH. Usually, the level of TSH in the blood is the best predictor of thyroid function.

• If the TSH levels are high, the thyroid is underactive. It’s called hypothyroidism.
• If the TSH is very low, the thyroid is overactive. It’s called hyperthyroidism.

Hypothyroidism

Simply put, this is an underactive thyroid gland and leads to inadequate production of the thyroid hormones and a slowing of vital bodily functions.

Clinical picture

• Facial expressions become dull
• Voice is hoarse
• Speech is slow
• Eyelids droop
• Eyes and face become puffy (myxoedema)
• Hair becomes sparse, coarse and dry
• Skin becomes coarse, dry, scaly and thick
• Fatigue is common
• Weight gain
• Constipation
• Muscle cramps
• Unable to tolerate cold
• Older people may become forgetful; can easily be mistaken for Alzheimer’s disease
• People with hypothyroidism have high levels of cholesterol

Causes of hypothyroidism

Primary hypothyroidism is due to a disorder of the thyroid gland. The most common causes are:

• Hashimoto thyroiditis is an autoimmune disease where antibodies are formed against the thyroid gland and eventually destroy it.
• Thyroid inflammation (thyroiditis) is caused by a viral infection and is usually temporary.
• Treatment of thyroid cancer or hyperthyroidism treatment.
• Lack of iodine in the diet is common in many developing countries. South Africa’s iodine is added to salt to prevent this.
• Radiation of the head and neck due to the treatment of cancers.

Diagnosis of hypothyroidism

Measurement of the TSH levels in blood. If this value is high, then a second test of T4 can be done to confirm that it is low.

Treatment

Replacement of the thyroid hormone using oral preparations. The preferred form of hormone replacement is synthetic T4 (levothyroxine).

Hyperthyroidism

Simply put, this is an overactive thyroid gland and leads to high levels of thyroid hormones and speeding up of vital body functions.

Clinical picture

• Heart rate and blood pressure increases
• Heart rhythm may be abnormal
• Excessive sweating
• Feeling of anxiousness
• Difficulty in sleeping
• Weight loss without trying
• Increased bowel movements
• Hand tremors
• Increased activity level despite fatigue and weakness
• Change in menstrual periods in women
• Changing in the eyes with a look of one that is staring

Causes of hyperthyroidism

The most common causes are:

• Graves’ disease is an autoimmune disorder. In this disorder the antibodies that are produced against the thyroid, stimulate it to produce more thyroid hormones. This leads to enlargement of the thyroid called a goitre. The eye symptoms are very pronounced with puffiness around the eyes, increased tear formation, irritation and sensitivity to light. This is sometimes called thyroid eye disease. Two distinctive signs are: bulging eyes (proptosis) and double vision (diplopia).
• Toxic multinodular goitre is a disease where there are multiple nodules (small lumps) in the thyroid. One or more produce excessive thyroid hormones. This is more common with ageing.
• Thyroiditis is inflammation of the thyroid that at first causes an overactive thyroid due to viral disease or auto antibodies (Hashimoto’s). The thyroid stores become depleted in time and this will lead to hypothyroidism.
• Single toxic nodule.

 

Diagnosis of hyperthyroidism

Measurement of TSH level in the blood. TSH level will be suppressed and T4 will be very high.

Antibodies against the thyroid can also be done to establish a cause.

Treatment

1. Treatment of the cause.
2. Betablockers to block the effect of the thyroid hormone and relieve the symptoms of palpitations, sweating, tremors and anxiety.
3. Sometimes medication (carbimazole) to block the production of the thyroid hormone.
4. Radioactive iodine to destroy the thyroid gland. This is the most common treatment of hyperthyroidism since it’s easy to administer a radioactive dosage of iodine that will destroy only the thyroid in a three-to-six-month period without surgery.
5. Surgery (thyroidectomy) to remove the thyroid or part of it. Sometimes eye surgery is needed in Graves’ disease.

Thyroid disease is a very common disease and should always be suspected. Treatment is highly effective, and any person can live a full life with the correct medical treatment.

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