Surgery notes
with Dr Graham Easton

7 December 2007

Is your thyroid underactive?

For a small gland, the thyroid can cause big problems. It's shaped a bit like a tiny bow tie and measures a few centimetres across. It sits just in front of your windpipe.

If you think of the cells and tissues of your body as an orchestra, then your thyroid is the conductor. It keeps your body functioning at the right pace. It works by producing a hormone called thyroxine, which is carried round the body in the bloodstream.

When it's not working hard enough it can cause all sorts of problems, ranging from fatigue and weight gain to skin changes and depression.

How to diagnose and treat an underactive thyroid has been the source of some prickly arguments among patients and doctors.

When your thyroid is underactive, called hypothyroidism, it doesn’t make enough thyroxine and this causes your body's functions (metabolism) to slow down. About one in 50 women and one in 1,000 men develop hypothyroidism at some time in their life.

By contrast, if you have hyperthyroidism, your thyroid is overactive and many functions start to speed up.

Hypothyroidism is usually easy to treat by taking a daily tablet to replace the missing thyroxine.

Is it really your thyroid?

The first challenge in the surgery is to get the diagnosis right - because the thyroid orchestrates so many body functions, the list of potential symptoms is daunting.

The commoner ones include: tiredness, weight gain, constipation, aches, feeling cold, dry skin, lifeless hair, fluid retention, depression, mental slowness, irregular or heavy periods, carpal tunnel syndrome, infertility and voice changes.

The problem for me is that all these symptoms are common and can be caused by other conditions. Having several on the list should raise my suspicions, but symptoms tend to develop gradually in an underactive thyroid, so they can go unnoticed for quite a while.

The solution - for doctor and patient - is to have the thyroid clearly on your radar. If it's always high up a GP's list of potential diagnoses then it's much less likely to be missed. That sounds easy enough, but the same could be said for the many thousands of other conditions that GPs need to bear in mind.

GPs need to remember to ask about potential thyroid symptoms you may not have noticed, and examine you for any obvious signs such as a swollen thyroid gland.

Once or twice patients have helpfully asked me whether it might be worth doing a thyroid blood test - and it was.

What do the blood tests really mean?

The good news is that thyroid function blood tests can help to diagnose an underactive thyroid and help to rule it out if your symptoms aren't clear cut. It's simple and relatively cheap, so there's no reason for not checking it if it's a possibility.

Some people, despite 'normal' blood tests, believe their symptoms suggest their thyroid is still underactive

One test measures levels of thyroid stimulating hormone (TSH), which is made by the pituitary gland and stimulates the thyroid gland to make thyroxine. It tends to be raised when your thyroid is underactive because it's trying to stimulate the thyroid to make more thryoxine.

The other main blood test measures levels of thyroxine (called T4) itself, and a low level of T4 suggests hypothyroidism. It's also possible to measure levels of T3, another form of thyroid hormone, which is mostly made in the body from T4.

This sounds straightforward but, unfortunately, there are times when the blood tests and symptoms don't seem to tally. This can cause confusion and frustration for both patients and doctors.

The first problem is when the TSH is high (suggesting an underactive thyroid) but levels of thyroxine, the thyroid hormone, are normal. This means you're making enough thyroxine, but the thyroid gland needs extra stimulation from the TSH to keep up.

There are currently two schools of thought about how to deal with this.

The first is simply to monitor your thyroid function over time, with repeat thyroid blood tests every so often. The evidence suggests half of patients in this category will become properly hypothyroid within ten years, at which time they can start treatment with replacement thyroxine.

The second approach is to start a trial of treatment with thyroxine in certain groups of patients - for instance, in patients with a goitre (a swollen thyroid gland), women who plan to become pregnant, or those with antithyroid antibodies in their blood (a common cause of hypothyroidism is the immune system making antibodies to your own thyroid).

Thyroid experts differ in their favoured approach, and often it comes down to individual circumstances.

How should hypothyroidism be treated?

The other controversy is how best to treat hypothyroidism. The usual treatment is with synthetic thyroxine (T4) and most people feel much better soon after starting it. You'll need regular blood tests to check how your thyroid is working, and your dose of thyroxine may be adjusted accordingly.

But some people, despite 'normal' blood tests, believe their symptoms suggest their thyroid is still underactive. They feel doctors are relying too heavily on blood test results rather than how their patient is feeling.

My opinion is there's often a fine balance when it comes to thyroxine replacement therapy - some patients feel healthier when their dose is tending towards over-replacement. Like many areas of medicine, this balancing act has to be a decision taken in partnership between doctor and patient.

If I'm reluctant to increase your dose of thyroxine when your blood tests suggest your thyroid is working normally, it's usually because I'm aware of the potential dangers of over-treating you. Patients receiving too much thyroxine are at risk of thinning bones and heart problems.

Some people also wonder about using T3 thyroid hormone, ususally in combination with the usual T4.

T3 is the active form of the thyroid hormone in the body. Except in rare cases, if you have enough T4 your body will naturally convert it to T3. T3 is a potent drug, is fast acting and can cause long-term problems if used excessively.

A recent review of evidence from proper clinical trials suggests a combination of T3 and T4 offers no overall improvement in symptoms or other physiological markers. At the moment, combination treatment isn't recommended by specialists.

Is natural best?

Finally, a real hot potato - a few patients have asked me about the value of using natural thyroid extract (Armour) instead of synthetic T4 as replacement. It's made from dessicated animal thyroid extract and contains both T3 and T4.

Emotions run high in this debate, but as a generalist I take my lead from medically qualified specialists in thyroid disorders.

The current advice from the British Thyroid Association is that Armour thyroid extract is not recommended as standard thyroid hormone replacement. This is because the amount of thyroid hormone is more variable between batches than it is in thyroxine tablets, and it contains potentially harmful levels of T3.

As a result, endocrinologists have abandoned using this in favour of the pure form of thyroxine, which is chemically exactly the same as that made by a normal thyroid gland.

Armour thyroid extract can be given through the NHS on a named patient basis, but it's not licensed in the UK, which means I would be required to take full responsibility for any adverse effects.

All content within BBC Health is provided for general information only, and should not be treated as a substitute for the medical advice of your own doctor or any other health care professional. The BBC is not responsible or liable for any diagnosis made by a user based on the content of the BBC Health website. The BBC is not liable for the contents of any external internet sites listed, nor does it endorse any commercial product or service mentioned or advised on any of the sites. See our Links Policy for more information. Always consult your own GP if you're in any way concerned about your health.