Myths and misunderstandings about the thyroid

Julia Priestley, CEO (Development) writes about some of the commonly held myths and misunderstandings about the thyroid and thyroid disease.

Diagnosing hypothyroidism with a thermometer

About 50 patients are admitted to UK hospitals every year, usually in the winter months, with myxoedema coma. Usually these are elderly patients who are severely hypothyroid and become very sick and hypothermic. Their body temperature can be very low and unfortunately many do not survive.

The connection between body temperature and thyroid function is well known. One of the common symptoms of hypothyroidism is cold intolerance. Thyroid hormones are major regulators of metabolism and heat production by the body. It is alleged that the diagnosis of hypothyroidism can be made by measuring body temperature which, if less than 37 degrees Celsius (98.6 degrees Fahrenheit), can signify hypothyroidism, even though thyroid blood tests may be normal. This is referred to in some circles as ʻWilsonʼs syndromeʼ though the World Health Organisation International Classification of Diseases does not recognise the existence of this entity. The American Thyroid Association placed an article on its website in 2005 on this topic and concluded: ʻThe American Thyroid Association has found no scientific evidence supporting the existence of ʻWilsonʼs syndromeʼ. The theory proposed to explain this condition is at odds with established facts about thyroid hormone. Diagnostic criteria for ʻWilsonʼs syndromeʼ are imprecise and could lead to misdiagnosis of many other conditions. The T3 therapy advocated for ʻWilsonʼs syndromeʼ has never been evaluated objectively in a properly designed scientific study. Furthermore, administration of T3 can produce abnormally high concentrations of T3 in the blood, subjecting patients to new symptoms and potentially harmful effects on the heart and bones.ʼ http://bit.ly/2mhIHMd

A lot more scientific evidence has accumulated since 2005 about the definition of normal body temperature, and it is worth highlighting one study from the USA that was published at the end of last year (Obermeyer Z, Samra JK, Mullainathan S. Individual differences in normal body temperature: longitudinal big data analysis of patient records. BMJ. 2017 Dec 13;359:j5468). What is remarkable about this study is the number of subjects included, which were no less than 35,488. The authors excluded children, people with infections and people with severe illnesses. The main finding was that the average temperature of these people was 36.6°C. In fact 95% of the population had a temperature between 35.7°C and 37.3°C. Or put another way, if the cut-off figure of 37°C was to be applied, more than 3/4 of the normal population would have to be classified as hypothyroid.

Interestingly, some of the subjects in this study (2,485, or 7% of the total) had a diagnosis of hypothyroidism (presumably on treatment, though no details were provided) and there was a weak statistical association between hypothyroidism and a lower body temperature.

Is possible that this association reflects the well known fact that more than 10% of patients who are on thyroid hormone replacement are inadequately treated and have an elevated serum TSH (Flynn RW, Bonellie SR, Jung RT, MacDonald TM, Morris AD, Leese GP. Serum thyroid-stimulating hormone concentration and morbidity from cardiovascular disease and fractures in patients on long-term thyroxine therapy. J Clin Endocrinol Metab. 2010;95:186-93).

So, most normal people have a body temperature of less then 37 degrees. Although there is an association between body temperature and hypothyroidism, the body temperature test as a diagnostic tool for hypothyroidism performs poorly, in fact less well than flipping a coin.

Adrenal fatigue and adrenal insufficiency

Adrenal fatigue is a name often given to a group of non-specific symptoms that can include tiredness, sleep problems, body aches, digestive problems and nervousness. These are all non-specific problems which are common to other diseases but widely experienced in modern, busy lifestyles.

There is no scientific evidence that this diagnosis exists and doctors are concerned that, if you are told you have this condition, the real cause of your symptoms may not be found and treated correctly. Also, treatment offered for adrenal fatigue is likely to be ineffective and expensive.

Adrenal insufficiency, however, is a real and diagnosable disease. Sometimes known as Addisonʼs disease or hypoadrenalism, it is a rare, potentially fatal condition which is caused by damage to the adrenal glands or a problem with the pituitary gland. A person with adrenal insufficiency may be dehydrated, confused, or losing weight. They may feel weak, tired, or dizzy and have low blood pressure. Other symptoms include stomach pain, nausea, vomiting, and diarrhoea. Adrenal insufficiency is diagnosed through blood tests and will require life-long, daily treatment with replacement steroid hormones. For further information go to the Addisonʼs Disease Self- Help Group website (http://www.addisons.org.uk/)

Beware thyroid test services by post

There is a small, but increasing, industry in the UK where private laboratories will measure your thyroid tests through a finger-prick blood sample, or in your saliva or urine. Some even offer genetic tests by post, such as the deiodinase-2 gene (DIO2) variant. These companies will suggest that these tests are better because they are ʻnot available on the NHSʼ. However, these tests are not offered by the NHS because they are unnecessary, a waste of money and the results are frequently meaningless.

One example is reverse-T3 (rT3), which is an inactive degradation product of thyroxine. Firstly, rT3 is really difficult to accurately measure because it ʻlooksʼ so similar to thyroxine. With the exception of specialist university laboratories, there is a high chance that what is calculated as your rT3 measurement is actually a highly inaccurate random number. Of course, you will have no way of knowing. Secondly, there is no situation where knowing your rT3 can usefully guide your clinical management. If it was useful, NHS labs would be measuring it.

Taking iodine supplements to support thyroid function

For people with a properly functioning thyroid, iodine is essential as it is required for the production of thyroxine. It is particularly important in women who are pregnant as it is needed to ensure the development of a babyʼs brain during pregnancy and early life.

People who are taking levothyroxine, however, do not have a functioning thyroid to absorb iodine and therefore iodine is not required. For patients being treated for hyperthyroidism, taking an iodine supplement is unnecessary and can worsen the condition.

Health food shops are often keen to promote supplements containing iodine or kelp to support normal thyroid function, the production of thyroid hormones, boost your energy levels and even help weight loss. Unfortunately there is no evidence that these supplements can do any of these things. In fact some may even damage your thyroid as they often contain excessive amounts of iodine, even if taken within the dose recommendations on the label.

Flu jabs, vaccinations and thyroid disorders

We regularly hear from people who have concerns about vaccinations asking whether or not they are safe for people with thyroid disorders. The flu vaccination programme is very well thought through and we are fortunate in the UK to live in a part of the world where vaccinations are freely available.

Having a thyroid disorder does not give you an increased risk of developing flu compared to any other member of the general population. Therefore, unless you fall within one of the following categories who are at greater risk of complications from the flu you are unlikely to need or be offered the flu vaccine:

  • people aged 65 and over
  • children and adults with an underlying health condition such as long-term heart or respiratory disease
  • children and adults with weakened immune systems

Teenage girls are now routinely offered the HPV vaccine which protects women against developing cervical cancer. There is no reason why a girl who has been diagnosed with a thyroid disorder should not be given this important vaccination.

If you have any particular concerns about your vaccinations you should always discuss these with your doctor.

Can dental x-rays harm your thyroid? And can RAI treatment act as a trigger in airport security detectors?

Some patients who have regular dental x-rays raise concerns that the exposure to radiation may damage their thyroid and they should therefore be offered neck guards as protection. One BTF medical adviser assures us that the amount of radiation from a dental x-ray is very small and, therefore, he does not think that occasional mouth x- rays during dental check-ups will harm your thyroid.

If you have recently had radioactive iodine ablation for the treatment of thyroid cancer, you may trigger radiation detectors used for security purposes, for example at airports and seaports. This can occur for up to 95 days after treatment. If you are travelling within this time period you should carry a letter from your hospital to explain your situation.

Are the TSH reference ranges too wide and, if so, should they be narrowed?

There are arguments for and against but what really matters, for most people who are being investigated or treated for thyroid disease, is interpreting the results of the blood tests in the context of the individual and his or her symptoms, so that sensible decisions can be made.

Reference ranges are a guide to defining the limits of normality and helping doctors in making a diagnosis. Any blood test can sometimes be misleading unless its limitations are understood, and tests should not be done unless there is a specific question that it is expected to address.

Reference ranges are derived from testing for a particular chemical such as TSH in the healthy, normal population. To ensure that only the most representative values are included, references ranges do not include the most extreme 5% of values. If the TSH is measured in randomly selected people without any known thyroid disease, there will be a range of values, with roughly two-thirds being around 1-2 milliunits per litre (mU/L).

If we go through the same exercise of working out a TSH reference range, but now apply more strict criteria (for example excluding people with thyroid antibodies or with minor abnormalities in their thyroid ultrasound scan), the reference range is narrower. However, this is complicated by the fact that if we do the same for older people, the upper limit of the reference range goes up. The same is true for some ethnic groups (African Americans) and people with obesity. Conversely, the reference range in pregnancy goes down and the TSH reference range in one geographical area may differ from another because of differences in iodine intake.

Although some might argue that by keeping the range wide some patients with the earliest signs of thyroid damage are being missed, any narrowing of the reference range inevitably means that people with normal thyroid function are at risk of being over-diagnosed and over-treated. Since there is no known clinical benefit from treatment in people with a TSH at the upper end of the conventional reference range, the current consensus is not to narrow this range further.

Is TSH testing sufficient or should doctors routinely test T4 and T3 levels?

In the majority of people, a TSH test alone is sufficient. If the TSH level is not normal, further tests including free T3 (FT3) and/or free T4 (FT4) may be useful and an antibody test may be required. In people recently treated with radioactive iodine for hyperthyroidism, or patients with known or suspected pituitary disease, FT4 should also routinely be checked.

In more than 99% of people with a normal TSH and who have no other reason to have a thyroid or pituitary problem, FT4 and FT3 will also be normal. If all three tests were performed routinely, then around £6m pounds a year would be spent unnecessarily. In someone without thyroid disease, if the TSH is raised then it should be repeated with a FT4 level. If persistently raised, then measuring an anti-TPO Ab tests is useful (but only on one occasion – it is only useful to know whether it is positive or not, the actual level does not contribute much additional information). If the anti-TPO Ab test is positive, it is more likely that the thyroid level may deteriorate over the coming months or years. Thyroglobulin antibodies (TgAB) generally do not add much to anti-TPO Ab results.

If the TSH is low, FT3 and FT4 measurement will diagnose hyperthyroidism. If confirmed, a TSH receptor antibody test looking for Gravesʼ disease is reasonable. In patients with known or suspect pituitary disease, the TSH level is misleading and FT4 should be measured. This is also true in other situations, such as within three months of treatment of hyperthyroidism (when the TSH may stay lower than it should be) and with some genetic abnormalities of thyroid function. If a patient has a normal TSH but persistent symptoms suggestive of hyperthyroidism or hypothyroidism, the measurement of FT4 and FT3 on one occasion is helpful to rule out a pituitary problem or these other rare conditions.

When monitoring patients already on thyroid hormone, TSH measurement alone is sufficient. If the TSH is not normal, FT4 (and possibly FT3) should also be measured. An exception is patients taking T3 alone, or in mixed preparation, when a FT3 measurement might be helpful. Follow- up measures of antibody tests are not normally required.

Does vitamin D, or its deficiency, have a role in the development of thyroid disease?

Some, but not all, observational studies have found low blood levels of vitamin D in patients with hypothyroidism (under-active thyroid) as well as hyperthyroidism (over-active thyroid) due to Gravesʼ disease. It is not clear from these studies if low vitamin D is a cause, a consequence, or an innocent bystander in the development of these common thyroid conditions.

It is possible that low vitamin D may permit the under-performing immune system to facilitate progression of thyroid disease. Equally, it is also possible that people with thyroid diseases may have altered health or lifestyles that lead to a low vitamin D state. For example, patients with an over-active thyroid due to Gravesʼ disease may increase the breakdown of vitamin D into inactive products. Those with an under-active thyroid may spend less time outdoors due to tiredness and thus have reduced sun exposure. Only properly conducted scientific trials will be able to answer this question in a definitive manner.

With thanks to Prof Simon Pearce, Dr Petros Perros and Dr Salman Razvi for their help with this feature.