Thyroid for Dummies (26 page)

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Soy beans also interfere with thyroid function, preventing the production of thyroid hormone in the thyroid gland (check out Chapter 10). Again, sufficient iodine can overcome the block and permit normal production of thyroid hormone, but when iodine is scarce, this extra loss of thyroid hormone makes a huge difference.

A third group of foods that contribute to endemic cretinism is the
Brassica
group of vegetables, which includes foods such as broccoli and cauliflower.

Hypothyroidism is more common in areas where these vegetables make up a large part of the diet and the diet is deficient in iodine.

Other foods that impair thyroid hormone production and are significant sources of food calories in certain areas of the world are ߜ Bamboo shoots

ߜ Sweetcorn

ߜ Lima beans

ߜ Sweet potatoes

Another important contributing factor in the development of iodine deficiency disease is the absence of another trace element, selenium, in the diet in certain areas, especially in China, Siberia, Korea, Tibet, and Central Africa.

These places are where iodine deficiency is already present. Selenium is a mineral that the body needs in order to create the enzyme that turns T4 into the more potent T3.

In fact, selenium plays an important role in reducing the number of goitres associated with iodine deficiency. The enzyme in the thyroid that selenium helps to produce also has the function of disposing of hydrogen peroxide, a side product of thyroid hormone production. When selenium is lacking, a build up of hydrogen peroxide may destroy thyroid cells, leading to a small thyroid.

This small thyroid is still not healthy, however, despite the lack of a goitre.

When both selenium and iodine are absent from the diet, a condition called
Kashin–Beck disease
develops. This disease can lead to short stature as a result of the destruction of the growth-plates at the ends of the long bones.

The damage is different than that seen in the short stature associated with myxoedematous cretinism, which this chapter describes later.

Goitre: The body’s defence

The thyroid and the rest of the body do what they can to prevent hypothyroidism. The first response is a fall in the production of T4 (refer to Chapter 3

for more on T3 and T4). When this drop occurs, the pituitary gland doesn’t 18_031727 ch12.qxp 9/6/06 10:43 PM Page 141

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sense sufficient T3 in the brain and responds by secreting more TSH (refer to Chapter 3). The thyroid reacts by getting larger – thus, forming a goitre – and by making more of the active hormone T3 (relative to the amount of T4). At the same time, the body converts more T4 into T3 away from the thyroid.

If the intake of iodine is severely limited, T3 production starts to fall. The consequence is severe hypothyroidism, which is particularly damaging to the brain.

Neurologic cretinism

The belief is that neurologic cretinism results from a lack of thyroid hormone from the mother during the period of the third to the sixth month of pregnancy.

The severe lack of iodine means that the growing foetus is unable to make thyroid hormone, either. During this time period, the brain needs enough thyroid hormone to develop the ability to hear as well as perform important motor (movement) functions, which are the abilities most affected in this form of cretinism.

Neurologic cretinism has three major characteristics: ߜ Mental impairment, although memory and social functions are unaffected ߜ Deafness and often loss of speech

ߜ Stiffness of the arms and legs and an increase in the reflexes (opposite to what is expected in hypothyroidism). The result is that this individual has a shuffling gait or is unable to walk at all.

A person affected by neurologic cretinism may not develop hypothyroidism later in life. If that person receives sufficient iodine, their thyroid makes sufficient thyroid hormone. But, sadly, the damage due to the lack of thyroid hormone during development of the brain is irreversible.

Myxoedematous cretinism

People with myxoedematous cretinism are not as mentally impaired as those with neurologic cretinism. They aren’t usually deaf or mute as a result of their condition. Instead, they demonstrate the signs and symptoms of severe hypothyroidism from birth, including:

ߜ Very dry, scaly, and thickened skin

ߜ Reduced growth

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ߜ Thin hair, eyelashes, and eyebrows

ߜ Puffy features

ߜ Delayed sexual maturation

People with this condition do not have enlarged thyroids, but their thyroids are often replaced with scar tissue. As a result, their uptake of radioactive iodine is reduced despite having very high TSH levels. The levels of T4 and T3 hormones are very low. Many individuals have a combination of these two conditions.

Just why such a difference exists between the two conditions isn’t clear, although a study published in 1988 sheds some light on this subject. In Qinghai Province in China, researchers found people with both neurological and myxoedematous cretinism along with a mixed group that showed signs of both conditions. The difference between the types of cretinism is explain-able by the length of time that these individuals were hypothyroid after birth; those people with myxoedematous cretinism appear to suffer hypothyroidism for a longer time than those with neurologic cretinism.

Individuals with neurologic cretinism develop mental impairment from a lack of thyroid hormone during brain development, but then get enough iodine to produce normal amounts of thyroid hormone after they are born. So, individuals with myxoedematous cretinism show signs of thyroid destruction, while those people with neurologic cretinism have normal thyroid function. The conclusion of the researchers is that these two disorders are actually the same, only modified according to the amount of hypothyroidism experienced after birth.

Managing the Problem

of Iodine Deficiency

You may think that managing the problem of iodine deficiency disease –

preventing all goitres, cretinism, thyroid-related physical and mental impairment, plus hypothyroidism – is relatively easy. The trick is just to get everyone to eat sufficient iodine. The adult daily requirement is just 150

micrograms of iodine – which amounts to a mere, microscopic pinch. Over the lifetime of an individual, only a teaspoon of iodine is required. But consuming enough iodine is much easier said than done. And sufficient iodine consumption must occur prior to the conception of a baby in order to prevent the occurrence of cretinism.

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A sprinkle of salt

The richest food source of iodine is seafood (fish, crustaceans, seaweed) and, to a lesser extent, milk, eggs, and meat. Fruits and vegetables contain very little iodine. Using iodine-rich foods to solve the problem is not possible, though, as diets and tastes differ throughout the world, and the logistics of transporting sufficient daily amounts of fish, milk, eggs, or meat to everyone in the world are overwhelming.

Iodisation in Bangladesh

The history of efforts to overcome iodine defi-

Bangladesh are producing salt with insufficient

ciency disease in Bangladesh serves as an

iodine. In a country with a population the size of

excellent illustration of the problems that are

Bangladesh, this amount represents inadequate

encountered. Research shows that only 55 per

iodine intake for millions of people.

cent of households in Bangladesh consume

Some of the so-called iodised salt is not iodised

iodised salt, despite international efforts to rid

at all in Bangladesh so that the provider can

the nation of iodine deficiency.

make an extra profit. Salt is sometimes brought

Bangladesh is subject to annual flooding with

in from other countries, mislabelled as iodised,

monsoon rains that effectively wash all iodine

and sold for a cheaper price than Bangladesh

out of the soil. The iodine washes into the Bay of

iodised salt. Bangladesh borders on Myanmar

Bengal, which means that fish caught there con-

(formerly Burma) and India, countries that are

tain plenty of iodine. However, most of the popu-

not as strict in enforcing iodisation. So smug-

lation of the country lives in rural areas far away

gling contributes to iodine deficiency disease in

from the supply of iodine. As a result, more than

Bangladesh as well.

50 million people in Bangladesh have goitres.

One step in the right direction is the develop-

Since 1984, a Law of Iodination makes the sell-

ment of a simple kit by UNICEF (The United

ing of salt in Bangladesh without it being iodised

Nations Children’s Fund) that detects whether

illegal, although penalties for this only came into

salt contains iodine. A drop of liquid solution

force in 1992. The cost of iodised salt in

added to salt turns the salt blue if iodine is pre-

Bangladesh is 14 pence per kilogram, while

sent. These kits are distributed to school chil-

non-iodised salt is 8 pence per kilogram, so the

dren, who test their salt at home.

poorest families buy the cheaper salt.

You can see that a successful iodisation pro-

The cost of iodising salt is less than 3 pence per

gramme involves much more than passing a law

person per year. The process is very simple,

and setting up salt iodisation processing in salt

carried out in a salt factory. But tests of iodine in factories. A mountain of barriers can block such

salt show that as many as half the factories in

a simple solution.

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Because virtually every culture in the world uses salt, which is cheap and simple to iodise, iodised salt is the standard way of overcoming the problem of iodine deficiency disease. The amount of salt needed to carry the daily requirement of 150 micrograms of iodine is very small and easily consumed.

In many countries, salt iodisation works well, but in some areas the goal of eliminating iodine deficiency disease is not yet achieved.

One major organisation, the International Council for the Control of Iodine Deficiency Disorders (ICCIDD), serves as the central organisation for coordi-nation efforts worldwide. This organisation has a global iodised salt logo, which manufacturers place on packages of salt that are properly iodised (see Figure 12-2).

Figure 12-2:

The global

iodised

salt logo.

An injection of oil

A highly effective way of managing iodine deficiency disorder is to inject iodised oil into the muscle of iodine deficient people. This substance is called Lipiodol, and a single injection provides enough iodine to last for four years or longer. An oral form of Lipiodol is also available, but it lasts little more than a year when taken this way. Iodine given through this oil can significantly shrink goitres in just a few months. However, giving iodine injections also has its problems.

Iodine deficiency is found in rural areas where administering sterile injections is not always possible. Similarly, qualified people are not always available to give the injections. Sufficient supplies of sterile needles and the iodised oil are needed and, in this age of acquired immune deficiency syndrome (AIDS), many people are reluctant to accept an injection. The oral form of Lipiodol, of course, solves all these problems.

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A slice of bread or cup of water

Other ways of managing iodine deficiency that are effective in some areas include the iodisation of bread and the addition of iodine to the water supply.

The problem with the iodisation of bread is that bread consumption varies widely, and so this method works only in limited areas. Adding iodine to water doesn’t work in areas with no public water supply, as is the case in most areas of the world where iodine deficiency disease is most prevalent.

Drawbacks of Iodisation

One major problem that occurs when iodisation programmes are undertaken is the occurrence of hyperthyroidism when a lot of iodine is given to a person whose thyroid is under hyperstimulation with TSH. This happens with iodine injections and even with iodised salt that contains excessive iodine. The tools for managing hyperthyroidism (refer to Chapter 6) in a rural environment are not always readily available, especially when dealing with a large number of cases.

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Chapter 13

Going In: Surgery on

the Thyroid Gland

In This Chapter

ᮣ Deciding whether you need surgery

ᮣ Picking the surgeon

ᮣ Preparing for surgery

ᮣ Understanding the procedure

ᮣ Managing after surgery

If you need a thyroid operation, the good news is that the thyroid is in a very convenient location. Positioned just a few millimetres beneath the skin of your neck, your thyroid gland is easily found. Except in rare circumstances in which the gland is matted down with fibrosis (check out Chapter 11 for more on
Riedel’s thyroiditis
) and difficult to free up, thyroid surgery is relatively simple in the hands of a skilled surgeon. Complications are few and infrequent, and the result of surgery is usually very satisfactory.