Underactive thyroid

What is an underactive thyroid?

An underactive thyroid (hypothyroidism) occurs when the thyroid gland stops producing enough of the thyroid hormones, triiodothyronine or T₃ and thyroxine or T₄. In its most common form, affecting one per cent of the population, mainly middle-aged and elderly women, the thyroid gland shrinks as its cells are all destroyed by a subtle defect in the patient’s immune system.

 

Less often this defect leads not only to hypothyroidism but to thyroid enlargement and the formation of a goitre. This is known as Hashimoto’s thyroiditis. These types of hypothyroidism are associated, as is Graves’ disease, with the other so-called ‘autoimmune diseases’ (see Glossary).

 

Although having hypothyroidism makes you more likely to develop one or more of these conditions than other people, the risk is still small. The other reason why people develop hypothyroidism is as a result of treatment of Graves’ disease by surgery or with radioactive iodine.

 

What is the pattern of development?

Hypothyroidism does not come on overnight but slowly over many months and you and your family may not notice the symptoms at first, or may simply put them down to ageing.

 

GPs now have ready access to the appropriate laboratory tests and, as a result, hypothyroidism is increasingly likely to be diagnosed at a relatively early stage when symptoms are mild. Hypothyroidism in its advanced state is sometimes known as ‘myxoedema’.

 

It would be unusual to have all the symptoms mentioned unless the diagnosis had been delayed for some reason for months or even years. You’re more likely to go to your GP with rather vague complaints such as tiredness and weight gain, which could be due to a variety of causes.

 

You’ll have a blood test and, if the result shows that you have low T₄ and high thyroid-stimulating hormone (TSH) levels, this will be confirmation that you are suffering from hypothyroidism. Unless there is a complication, such as angina, you will be treated by your family doctor.

 

Autoimmune diseases associated with hypothyroidism

•    Pernicious anaemia for which regular injections of vitamin B12 are necessary to maintain a normal blood count

•    Diabetes mellitus usually requiring treatment with insulin

•    Addison’s disease: the adrenal glands which sit on top of each kidney produce insufficient cortisol and aldosterone, hormones that fortunately can be taken as tablets

•    Premature ovarian failure which causes loss of periods, infertility and an early menopause

•    Underactivity of the glands adjacent to the thyroid, the parathyroid glands, leads to a low level of calcium in the blood and tetany which is effectively treated with vitamin D capsules

•    Vitiligo, a skin disease in which there are areas of loss of pigmentation, gives a ‘piebald’ appearance

 

Symptoms of hypothyroidism

Weight gain

Most patients gain from five to ten kilograms, although your appetite is normal or even less than usual.

 

Sensitivity to the cold

You’ll feel the cold very badly, and want to wear extra layers of clothing and sit close to the fire. You may well suffer from muscle stiffness and spasm when you move suddenly, especially when it’s cold.

 

Mental problems

Tiredness, sleepiness and slowing down intellectually. Your reactions get slow, but, fortunately, your sense of humour is unaffected.

 

Older patients may be wrongly thought to be suffering from dementia, while some people experience depression and paranoia, which are the basis for what is popularly known as ‘myxoedema madness’.

 

Speech

Your voice becomes slow and husky and speech is often slurred.

 

Heart

In contrast to a person with an overactive thyroid gland, your pulse rate is slow at around 60 beats per minute.

 

You may have high blood pressure and an elderly patient with severe long-standing hypothyroidism is at risk of heart failure. Angina may be the first symptom of hypothyroidism.

 

Bowel movements

You probably suffer from constipation.

 

Menstruation

Your periods become heavier (menorrhagia) if you haven’t yet had your menopause.

 

Skin and hair

Your skin is likely to be rough and dry and to flake readily. It tends to be pale and your eyelids, hands and feet swell. Some people may find that their skin has a lemon-yellowish tint and prominent blood vessels in the cheeks add a purplish flush.

 

Sitting too close to the fire can cause a ‘granny’s tartan’ to appear on the skin of your legs. Some people get the skin condition known as vitiligo. Your hair becomes dry and brittle and the outer part of your eyebrows may be missing.

 

Nervous system

You may become a little deaf and have trouble with your balance. If your fingers tingle, especially during the night, shaking your hands vigorously should relieve it.

 

Confirming the diagnosis

This requires a simple blood test to measure the levels of T4, which will be low, and TSH, which will be high. If these results are borderline, the measurement of antibodies directed against the thyroid (peroxidase antibodies) will tell whether you have underlying thyroid disease that may justify treatment with T₄ or whether your results, although at the extreme end of the reference range, are normal for you.

 

Treatment

This is with thyroxine which is available in the UK as 25, 50 and 100 microgram tablets. Normally, thyroxine treatment is begun slowly and you’ll be prescribed a daily dose of 50 micrograms for 3 to 4 weeks, increasing to 100 micrograms daily for a further 3 to 4 weeks and then to 150 micrograms daily.

 

You’ll then have another blood test some three months after starting treatment to assess whether any further minor adjustment of dose is necessary. The aim is to restore levels of T₄ and TSH in the blood to normal. You should start to feel better within two to three weeks; you’ll lose weight and notice the puffiness around your eyes disappearing quite soon, but your skin and hair texture may take three to six months to recover fully. Normally you’ll have to expect to stay on thyroxine treatment for life.

 

Very rarely, patients who have had an underactive thyroid for years develop an overactive gland as a result of Graves’ disease.

 

Case history: Jean

Jean Spencer was 17 and in her final year at school, hoping to go to university to study law. She had had diabetes since she was 11 and gave herself insulin injections twice each day.

 

Control of her diabetes had always been very satisfactory and her dose of insulin did not vary much. She had been puzzled, however, for the last three months because she did not seem to require as much insulin as before. On four occasions she had almost become unconscious in class because of a low level of glucose in her blood but had been brought round with sugary drinks by her teacher.

 

Once she did not respond and was rushed to hospital and given a glucose drip into a vein and kept in overnight. Jean’s parents and her teacher were also concerned because she was not concentrating in class and her results in the mock exams had not been nearly as good as expected. She had also begun to complain of the cold and had not been able to sing in the school Christmas concert because her voice had become husky.

 

It was her aunt, visiting from Canada, who recognised the change in Jean’s appearance since her visit the previous year. The aunt had developed an underactive thyroid gland 10 years earlier and suggested to Jean that she have a blood test. Jean is now taking thyroxine tablets, like her aunt, and her insulin dose has returned to its previous level. She passed her A levels with flying colours and is now in her first term at university studying law.

 

Special situations

Angina

The level of various fats or lipids in the blood is increased in hypothyroidism and, in people who have had the condition unrecognised for a long time, the coronary arteries can become narrowed by fatty deposits, a process called atherosclerosis. Insufficient blood reaches the heart muscle, especially during exercise, and the sufferer will get pain in the middle of the chest (angina).

 

Treatment with thyroxine may worsen the angina and someone with this problem will be started on a lower dose and have it increased more slowly than normal. It may be necessary to have an operation to improve the blood flow through the coronary arteries before or after starting thyroxine treatment.

 

Temporary hypothyroidism

Treatment with thyroxine is usually for life. However, if you develop hypothyroidism in the first three to four months after surgery or radioactive iodine treatment for Graves’ disease it may be short-lived, lasting only a few weeks, and you may not need any treatment. The same is true for the hypothyroidism that is a complication of postpartum (after childbirth) thyroiditis or de Quervain’s thyroiditis.

 

Mild hypothyroidism

Most GPs will arrange for someone to have a blood test even when they only suspect thyroid problems, so quite minor abnormalities are often picked up in patients who come because of a variety of rather vague symptoms, such as tiredness, or in people who have a family history of autoimmune disease.

 

The most common finding is the combination of a ‘normal’ T₄ but raised TSH level, known among doctors as subclinical hypothyroidism. It is known that around 5 to 20 per cent of these people will develop more obvious hypothyroidism in each following year. For this reason, it is now common practice to ‘nip things in the bud’ by prescribing thyroxine when the abnormality has been found on more than one occasion. This may not have any dramatic effect on the individual concerned, but preventive medicine is better than cure.

 

Hypothyroidism caused by drugs

One drug, called lithium carbonate, which is widely used for depression and mania, may cause goitre and hypothyroidism. When, as normally happens, a person needs to keep taking lithium carbonate, continued treatment with thyroxine will be necessary.

 

Amiodarone, used in the treatment of certain heart irregularities, may cause not only hyperthyroidism but also hypothyroidism and anyone who is taking it will need regular thyroid blood tests.

 

Change to your usual dose of thyroxine

The dose of thyroxine may need to be increased during pregnancy, if there is malabsorption of food by the bowel, such as in coeliac disease, or lack of acid secretion by the stomach as in pernicious anaemia or while taking anti-ulcer drugs, such as omeprazole. There is an increasing list of medicines that reduce the absorption of thyroxine or speed up its breakdown by the body. If you need more thyroxine, the TSH level will increase significantly, having previously been normal.

 

Thyroxine is now manufactured in the UK by a variety of companies. This is known as generic thyroxine and, despite rigorous controls, doctors and patients have noticed from blood test results and from symptoms that there may be a variation in tablet strength between different manufacturers. For this reason, it is wise to insist that the same make of thyroxine is dispensed by the pharmacist when you renew the prescription. If it is not possible to provide the same make, you should consider having a blood test some six to eight weeks after starting the new preparation.

 

Possible future treatment

Most patients with hypothyroidism feel perfectly well while taking an appropriate amount of thyroxine, as judged by measurement of T₄ and TSH in the blood. However, some patients do not achieve the sense of well­being expected, even if a little extra thyroxine is taken, which results in a low rather than a normal TSH level.

 

If you are one of this small group of patients, there is some evidence, which needs to be confirmed, that a combination of thyroxine and the other thyroid

hormone, T₃ (triiodothyronine), may be beneficial.

 

If you change to this combined treatment, the dose of thyroxine should be reduced by 25 to 50 micrograms and half a tablet (10 micrograms) of T₃, also known as liothyronine, added.

 

In the interim some patients are turning to an old-fashioned medicine, thyroid extract, made from the thyroid gland of animals, which contains both T₃ and T₄ (Armour thyroid). These tablets are not readily available in the UK and, because of continuing anxieties about the reliability of their hormone content, their use is not recommended.

 

It makes sense to replace what is missing when the thyroid gland stops working and the ideal replacement tablet would contain about 100 micrograms T₄ and 10 micrograms T₃, the latter in a slow-release form. This would avoid peak levels of T₃ in the blood after taking the medication, which can produce troublesome palpitations. Unfortunately such an ideal medicine has not yet been produced by the pharmaceutical industry.

KEY POINTS

• Hypothyroidism usually comes on slowly and your symptoms are likely to be vague at first

• Your GP will be able to confirm the diagnosis with a simple blood test

• Treatment is with tablets, which you’ll probably need to take for the rest of your life

• Some people who have been hypothyroid for many years may suffer from chest pain caused by angina and, because thyroxine aggravates the problem, their dosage will need careful monitoring. If you already have angina when your thyroid condition is first discovered, your treatment will be adjusted to take account of this

• If your thyroid blood test is only slightly abnormal, you may be given preventive treatment with thyroxine