Family Doctor Books


Published in association with the British Medical Association


© All words and images shown within this site are protected by copyright.
 
Family Doctor Books
Sample chapter - Understanding Thyroid Disorders

An overactive thyroid gland (hyperthyroidism or thyrotoxicosis) results from the over-production of the thyroid hormones, T4 and T3, by the thyroid gland. In three quarters of patients this is the result of the presence in the blood of an antibody that stimulates the thyroid, not only to secrete excessive amounts of thyroid hormones but also, in some, to increase the size of the thyroid gland, producing a goitre. This type of hyperthyroidism is known as Graves’ disease, named after one of the physicians who described the condition in considerable detail over 200 years ago.

The cause of the antibody production is not known but, as Graves’ disease runs in families, genes must play a part. There is thought to be some environmental trigger that starts off the disease in genetically susceptible individuals, but the culprit has not been identified. Stress, in the form of major life events, such as divorce or death of a close relative, may play a role.

Some patients with Graves’ disease develop prominent eyes (exophthalmos or proptosis) and a few also suffer from raised, red, itchy areas of skin on the front of the lower legs or on the top of the feet, which are known as pretibial myxoedema. These, like the production of the thyroid-stimulating antibodies, are caused by an abnormality in the patient’s immune system which doctors don’t yet fully understand. Most other patients with hyperthyroidism have a goitre containing one or more nodules or ‘lumps’. These over-produce thyroid hormones in their own right and are not under the control of TSH, as is the normal thyroid gland.

Graves’ disease can come on at any age but most commonly affects women in the 40–50 age group. Between a third and a half of all patients will have a single episode of hyperthyroidism lasting several months. The rest will have successive episodes of hyperthyroidism over many years. Unfortunately, it is not possible to predict the pattern of hyperthyroidism when it first occurs. Hyperthyroidism resulting from a nodular goitre is unusual before the age of 40 and, unlike in some patients with Graves’ disease, it persists indefinitely once it has developed.

An overactive thyroid gland

In retrospect, most patients will have had symptoms for at least six months before they go to see their doctors, but in some, usually teenagers, the onset is more rapid with symptoms present for only a few weeks. Not all patients with hyperthyroidism have all the symptoms listed below. In elderly people the predominant features, in addition to weight loss, are often a reduction in appetite, muscle weakness and apathy. A young woman, on the other hand, may appear to be full of energy and be unable to sit still for more than a few seconds.

Symptoms

  • Weight loss: This happens to almost all patients as a result of a ‘burning off’ of calories caused by the high levels of thyroid hormones in the blood. You will probably find you’re hungry all the time, and that you even have to get up in the night to get something to eat. The degree of weight loss varies from 2–3 kilograms to as much as 35 kilograms or more, but a few people find that their appetite increases to such an extent that they may gain a little weight. If you are severely overweight when the condition first starts, you’ll probably be delighted to find that you’re losing weight and put it down to dieting, but sadly you’ll put the weight back on once you’re being treated.

    The extent of weight loss is confirmed on the scales. Patients sometimes delay seeing their doctors because they are worried that the weight loss is caused by cancer and do not wish to have their worst fears confirmed.

  • Heat intolerance and sweating: As metabolism is increased, your body produces excessive heat which it then gets rid of by sweating. You won’t enjoy warm weather or a centrally heated environment and may feel comfortable scantily dressed on a crisp winter’s day. In extreme cases, your inability to tolerate heat may lead to disagreements with friends and colleagues as you’re constantly turning heating thermostats down, opening windows and tossing blankets or duvet off the bed.

  • Irritability: This most often affects women with a young family. You may find yourself increasingly unable to cope with the demands and stresses of looking after the children, lose your temper frequently, and find that you’re abnormally sensitive to criticism, bursting into tears for no apparent reason. You may find it difficult to concentrate, which can adversely affect your performance at school, college or work.

  • Palpitations: Most patients experience palpitations, or you may be aware of your heart beating at a faster rate than normal. In severe, long-standing, untreated hyper-thyroidism, particularly in elderly people, there may be an irregular heartbeat, known as atrial fibrillation, and even heart failure.
  • Breathlessness: This is most likely to be noticeable when you’ve exerted yourself, for example, after climbing two or three short flights of stairs. Asthmatic individuals may notice a worsening of their symptoms.

  • Tremor: Most patients complain of shaky hands which may be mistaken by friends and relatives for the tremor of alcoholism. You’ll find it difficult to hold a cup still or insert a key into a lock and your handwriting may deteriorate.

  • Muscle weakness: Characteristically, the thigh muscles become weak, making it hard to climb stairs or to get up from a squatting position or a low chair without using your arms.

    • You may find that you lose your temper frequently

  • Bowel movements: There tends to be an increase in their frequency such that you pass a softer than normal stool two or three times daily. Diarrhoea can occasionally be a problem.

  • Menstruation: Periods are often irregular, light or even absent. Until the hyperthyroidism is adequately treated it may be difficult to conceive.

  • Skin, hair and nails: You may find that your whole body itches, and people with Graves’ disease, as mentioned earlier, may develop raised itchy patches on their lower legs and feet (pretibial myxoedema). Your hair will probably become thinner and finer than usual and won’t take a perm very well. Your nails will be brittle and become rather unsightly.

  • Eyes: It is only those patients with Graves’ disease who have trouble with their eyes. Problems include excessive watering made worse by wind and bright light, pain and grittiness as if there is sand in the eyes, double vision and blurring of vision. Many sufferers are also naturally upset because they develop exophthalmos (protruding eyes) as well as ‘bags’ under their eyes.

  • Goitre:Although you will obviously be able to see when you have a goitre, it’s unlikely to cause any actual symptoms other than a sensation that there is something in your neck that shouldn’t be there.

    A goitre is felt or seen as a swelling in the neck.

Confirming the diagnosis

You’ll probably have had a blood test taken at your health centre or GP’s surgery, but you may well have more done for confirmation when you go to the outpatients’ clinic at the hospital. The specialist may also wish to carry out a thyroid scan to obtain more information about the cause of the hyperthyroidism as this may affect the type of treatment that you will need.

A thyroid scan requires a tiny dose of radioactive iodine or technetium to be given either by mouth or by injection into a vein. The dose is so small that it can even be given to someone who is known to be allergic to iodine. Most specialists, however, would try to avoid radioactive scanning if you are pregnant or breast-feeding.

After your GP has made the initial diagnosis, you’ll probably have to wait for a bit before you can see the hospital specialist. In the meantime, your symptoms may be eased by taking one of the beta-blocker drugs such as propranolol, which counteracts to some extent the actions of thyroid hormones. This is most likely to be in a dose of 40 milligrams to be taken three or four times daily or in the form of propranolol (Inderal-LA) 160 milligrams daily as a single dose by mouth. Beta-blocking drugs should not be taken by asthmatic individuals.

Treatment for Graves’ disease

There are three forms of treatment for the hyperthyroidism caused by Graves’ disease. These are drugs, surgery and radioactive iodine.

  • Drugs:Antithyroid drugs are usually given to younger patients who go to their doctor when they have their first episode of hyperthyroidism. The most commonly used drug in the UK is carbimazole which reduces the amount of hormones made by the thyroid gland. It is available as 5 milligram and 20 milligram tablets. A high dose (40 to 45 milligrams daily) is used initially and your symptoms should start to improve after 10 to 14 days. Normally treatment is continued for six to 18 months, after which up to half the patients will have recovered and remain well. To start with, your specialist will review your treatment every four to six weeks, and the dose of carbimazole will be reduced in stages down to 5 to 15 milligrams daily in a single dose, depending upon the results of measurements of your blood levels of T3, T4 and TSH. Some specialists prefer to give a high dose of carbimazole throughout treatment, usually as 40 milligrams daily, in the form of two 20 milligram tablets. If this high dose were to continue for several weeks or more, you would eventually develop an underactive thyroid gland and therefore thyroxine is added to the carbimazole once thyroid hormone levels have returned to normal. The advantage of this type of treatment is that it doesn’t need to be reviewed so often. It can also be particularly beneficial for patients with severe eye disease, but isn’t any more effective in controlling symptoms of hyperthyroidism than carbimazole alone.

    What you should know: few people will experience any side effects from taking carbimazole, but those who do usually develop them within three to four weeks of starting treatment. A skin rash affects two per cent of patients, but the more serious reaction is a reduction in the number of white blood cells which causes mouth ulcers and infection with a high fever. Your doctor should warn you about these possible effects when you first start the treatment. If you are affected, you should stop taking the drug and contact your GP straight away. You can then be given an alternative drug, called propylthiouracil, which works in a similar way to carbimazole.
  • Surgery: Unfortunately, despite taking carbimazole or propylthiouracil alone or in combination with thyroxine for up to 18 months, about half of all patients will develop hyperthyroidism again and usually within two years of stopping the drug. If you’re under 45 when you have your second bout of the condition, it may be treated surgically by removing about three-quarters of your thyroid gland.

    Before this operation can be done, however, it is necessary to restore thyroid hormone levels in your blood to normal with carbimazole. Once you’ve been given a date for the operation, you may be asked to take an iodine-containing medication for 10 to 14 days before surgery to reduce the size of the thyroid and its blood flow, which makes the job technically simpler for the surgeon. You’ll usually go into hospital the day before your operation, which lasts about one hour, and you’ll be allowed home between two and four days afterwards.

    What you should know: the disadvantage is that you will have a scar, but this usually becomes pale and unnoticeable among the other wrinkles in the neck. Alternatively you can wear jewellery or scarves to hide it. In very rare cases (less than one per cent), the parathyroid glands, which lie close to the thyroid and control the level of calcium in the blood, may be damaged, in which case long-term treatment with vitamin D tablets will be necessary. Equally rare is damage to one of the nerves supplying the voice box which may result in significant alteration to the quality of the voice. Although this wouldn’t matter very much to most people, it could make surgery a less acceptable option to anyone who depends upon their voice for a living – an opera singer, for example.

    In experienced hands the initial results of surgery are good. Eighty per cent of sufferers will be cured immediately. However, 15 per cent will have had too much thyroid tissue removed and so will be hypothyroid, whereas five per cent will have had insufficient thyroid tissue removed and remain hyperthyroid. These failures are not the result of surgical incompetence, but have more to do with the nature of the underlying thyroid disease. What’s more, over the passage of time, an increasing proportion of those patients whose hyperthyroidism was originally cured by surgery will develop an underactive thyroid gland. Recurrence of hyperthyroidism may even develop 20 to 40 years after apparently successful surgery. In the event of recurrent hyperthyroidism, it is unusual to consider a second operation because surgery will be technically difficult and the risk of damage to surrounding structures increased.

    Surgery may be the treatment of choice in a young patient with Graves’ disease and a large goitre.

  • Radioactive iodine (iodine-131): Traditionally this form of treatment is reserved for patients aged over 40 to 45 and beyond child-bearing age or for younger individuals who have been sterilised.This conservative approach was originally adopted because of concern that radioactive iodine might lead to any children conceived after treatment being born with abnormalities. In fact, there is no evidence for this, and in some hospitals there is a move towards using radioactive iodine in younger patients as it is cheap and easy to administer.

    Radioactive iodine is taken as a capsule or a drink that tastes like water, and is usually administered in hospital in a department of medical physics. Before receiving treatment you may be asked to sign a consent form, and will have received instructions about avoiding places of entertainment and close contact with colleagues and young children for a period of a few days after therapy. Radioactive iodine is never prescribed for pregnant women as it will adversely affect the fetal thyroid gland and women are advised to avoid pregnancy for four months after treatment.

    Radioactive iodine acts by destroying some of the thyroid cells and by preventing others from dividing, which is how they are normally replaced at the end of their lifespan. The treatment takes six to eight weeks to work and in the interim, depending upon the severity of the hyperthyroidism, you may be given propranolol or carbimazole to relieve your symptoms. You’ll be asked to come back to hospital for a check-up in two to three months and, if you’re one of the minority of people who is found to be still hyperthyroid, you’ll be given a second dose of radioactive iodine.

    What you should know: the major problem with this treatment is, however, the development of hypothyroidism. It’s most likely to appear in the first year after treatment, affecting about 50 per cent of people in some centres. In each year after that, around two to four per cent of people will be affected. It follows that the great majority become hypothyroid eventually and it is essential that you should have regular check-ups either at the hospital or with your GP. Once hypothyroidism has developed treatment is with thyroxine, ultimately in a dose of 100 to 150 micrograms daily. There are no side effects with thyroxine if the appropriate dose is taken regularly.

Case history

Although 70-year-old John Parry considered himself to be generally very healthy, he had recently noticed that his ankles were swelling. To start with, it was just at night, but then it happened all the time and his legs felt very heavy. One night at 1 a.m. he woke up gasping for breath and coughing up white frothy spit. His wife called an ambulance, and John was admitted to the local hospital within 20 minutes. The doctor on duty, Dr Mackenzie, correctly diagnosed heart failure as the cause of the fluid accumulation in John’s legs and lungs. He also noticed that John’s pulse rate was very rapid and irregular and an electrocardiogram showed this to be caused by atrial fibrillation. Mr Parry was given oxygen using a facemask, an injection of a drug called frusemide (Lasix) to get rid of the excess fluid, and digoxin tablets to reduce the speed of his heart beat. As patients with atrial fibrillation are at risk of throwing off blood clots from the heart, resulting in a stroke or a blocked artery in a leg, he was also given tablets called warfarin to thin the blood.

Dr Mackenzie had at one time worked with an eminent endocrinologist and knew that atrial fibrillation could sometimes occur as a complication of an overactive thyroid gland, particularly in older patients.

Mr Parry did indeed have hyperthyroidism which turned out to be caused by Graves’ disease and he was treated with radioactive iodine. He was also given the antithyroid drug, carbimazole, for six weeks until the radioactive iodine had time to take effect.

Although to begin with Mr Parry was concerned about the number of tablets he was taking when he left hospital, these had all been stopped within six months as his thyroid gland came under control. Even his heart is now beating regularly and he is as fit as ever. His GP carries out thyroid blood tests regularly to make sure that Mr Parry is not developing an underactive thyroid gland as a result of the radioactive iodine treatment.

Case history

Anna Robinson had had a previous episode of hyperthyroidism caused by Graves’ disease in her mid-twenties, for which she had been given an 18-month course of carbimazole. At the age of 45, she noticed that she was troubled by the heat, but put this symptom down to the ‘change of life’.

However, when she began to lose weight and her hands became shaky, she realised that her thyroid gland was overactive again. At the local hospital the specialist suggested that she should be treated with radioactive iodine. In spite of reassurances and the evidence that this form of treatment was not associated with any risk other than the eventual onset of an underactive thyroid gland, Mrs Robinson was uneasy. She was aware from articles in the news papers of a possible link between radiation and leukaemia in those living near to nuclear power stations, and she did not like the thought of avoiding her new grand-daughter albeit only for a few days after treatment.

As she was a keen singer in the local church choir, thyroid surgery was felt not to be appropriate because of the possibility of a change in the quality of her voice.

Mrs Robinson was relieved to learn that there was no reason why she could not be treated with carbimazole now or in the future.

WHICH TREATMENT IS RIGHT FOR YOU?
  • No treatment is perfect and you will need to discuss the options with your specialist. Some patients are not keen on surgery even when a course of antithyroid drugs has been tried and failed.
  • There is no reason why you shouldn’t have a second or even a third course in the hope that the disease will ultimately ‘burn itself out’. Indeed, before there was any form of treatment for the hyperthyroidism of Graves’ disease, a proportion of patients got better spontaneously after months or years and then became hypothyroid.
  • Some patients are unhappy at the prospect of radioactive iodine treatment and some specialists consider that the best treatment for a young patient with severe hyperthyroidism and a large goitre is surgery.
  • Whatever kind of treatment you have for hyperthyroidism, you will need regular follow-up, usually by an annual blood test taken at a health centre or your GP’s surgery.

Graves’ disease and the eyes

The eye signs of Graves’ disease (ophthalmopathy or orbitopathy) are present in most patients if the doctor looks hard enough. Sometimes these occur before the onset of the overactive thyroid gland and even for the first time after the successful treatment of the hyperthyroidism. One eye is often more affected than the other.

An early sign is retraction of the upper eyelid which appears as if it has been pulled up, exposing more of the white of the eye and causing a staring appearance. This may improve after the raised levels of thyroid hormone have been restored to normal with treatment. Some patients complain of dry, gritty eyes, as if there is sand in them, and of constant blinking, others of excessive watering.

The other features of thyroid eye disease result from a build-up of pressure behind the eyeball, which sits in a bony socket known as the orbit. The space between the eyeball and the back of the orbit contains the muscles that move the eye, the optic nerve which relays messages from the retina to the brain, and fat. In patients with thyroid eye disease, among other changes there is an accumulation of excessive amounts of water behind the eyeball, and the muscles and fat become swollen and boggy. The muscles double or treble in bulk and cease to work efficiently. As a result, the normal movement of the eyes may be restricted and uncomfortable, with double vision (diplopia) and even the development of a squint.

The increase in pressure behind the eyeballs pushes them forwards, producing the ‘pop-eye’ appearance known as exophthalmos or proptosis. The increased exposure of the protruding eyeballs makes them more prone to irritation from dust, grit, wind and sun, and the cornea may be damaged. In addition, some of the fat behind the eyeballs may be forced into the eyelids, contributing to their puffiness and the appearance of ‘bags under the eyes’. Very rarely, in severely affected patients, the increased pressure may damage the optic nerve and cause partial or total loss of vision.

Treatment of the eye disease is not as satisfactory as that of the overactive thyroid gland. Smoking is thought to make it worse as does poor control of the hyperthyroidism. It is very important, therefore, that you stop smoking completely and are careful to follow your doctor’s instructions about dosage of tablets, such as carbimazole or thyroxine. If you have dry eyes, you may find that a prescription for artificial tears helps, as it also does paradoxically for those with excessive watering. It is also worth wearing dark glasses when sunny.

Those with more advanced disease that threatens vision may need treatment with a steroid drug, such as prednisolone, which damps down the poorly understood processes leading to accumulation of water behind the eyeball. Alternatively, an operation may be required to remove part of the wall of the orbit, thereby reducing the pressure behind the eyeball. Such a major undertaking is rarely necessary, however, and would be carried out only after close collaboration between thyroid and eye specialists.

Most people with Graves’ disease find that their eye problems settle down considerably over a period of two to three years. At that stage, relatively minor surgery will correct double vision and reduce the ‘staring’ look and the bags under the eyes.

There is some evidence to suggest that the eye disease may deteriorate after treatment with radioactive iodine and some specialists will not wish to prescribe this form of therapy for anyone whose eyes are badly affected. In some centres, radiotherapy has been used with some success in the treatment of thyroid eye disease.

Thyroid-related eye disease usually has three phases, each of variable duration. Sfter an initial deterioation the condition should stabilise over a period of two to three years. Thereafter relatively minor surgery should correct any double vision and improve the cosmetic appearance of the eyes.

Nodular goitre

This is treated either with surgery or with radioactive iodine. Unlike someone with Graves’ disease, you’re unlikely to develop hypothyroidism.

It used to be fashionable after surgery to prescribe thyroxine to prevent regrowth of the goitre, which is common over a period of some 20 years, but this is not really useful unless you’ve developed hypothyroidism.

RARER TYPES OF HYPERTHYROIDISM
  • Mild hyperthyroidism, lasting for a few weeks, may occur after a viral infection of the thyroid; this is known as viral or de Quervain’s thyroiditis and the most prominent feature is severe pain and tenderness over the thyroid gland associated with symptoms of a ’flu-like illness. The hyperthyroidism rarely needs any treatment other than a beta-blocking drug, such as propranolol. There usually follows an equally short-lived period of mild hypothyroidism and then full recovery.
  • The iodine-containing drug, amiodarone, which is used increasingly by heart specialists for the treatment of certain irregularities of heart rhythm, may cause hyperthyroidism. Your blood thyroid hormone levels should be checked before you start taking the drug, and at six-monthly intervals while you’re on it
 
KEY POINTS
  • Around three-quarters of cases of hyperthyroidism are caused by Graves’ disease
  • Many people with Graves’ disease may have inherited a tendency to develop it, although other factors are also involved in triggering the condition
  • The people most likely to develop Graves’ disease are women between the ages of 40 and 50
  • Drugs, surgery and radioactive iodine are all possible ways of treating Graves’ disease, but there is no one treatment that is right for everyone
  • Your specialists may want to discuss the treatment options with you before making the final decision on which approach is best for you
  • After treatment, you will need regular check-ups to ensure that you stay well
  • Most people with Graves’ disease will experience some degree of eye problems, although they may be only minor irritations. More serious symptoms can be treated and usually settle in time