By Dr. Charles Shepherd
Following a recent discussion on several UK lists around the controversial subject of thyroid function and the use of thyroxine to treat myalgic encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS), here are a few key points on which I feel the vast majority of doctors involved in the management of ME/CFS patients would agree:
Before a diagnosis of ME/CFS is confirmed, thyroid function tests must form part of the routine (blood) investigations, because defective production of thyroid hormone/thyroxine (also known as hypothyroidism/myxoedema) can cause a number of ME/CFS-like symptoms. In a few people both conditions co-exist.
At the diagnostic stage, checking the blood levels of thyroid-stimulating hormone (TSH) and thyroxine (T4) is usually all that is necessary. The TSH test is very sensitive and measures the level of a hormone produced by the anterior pituitary gland in the brain, whose function it is to stimulate the thyroid gland (in the neck) to produce thyroxine. If natural production of thyroxine starts to fall, this is quickly picked up by thyroid hormone sensors and the TSH level starts to rise.
However, in the case of the much rarer secondary hypothyroidism (which is caused by problems with the pituitary or hypothalamus glands in the brain) there is a reduced level of T4 and a TSH level which is normal or below normal. Abnormalities in thyroid function tests can also be caused by drugs and other illnesses (including low levels of cortisol). As such, the interpretation of these test results isn't always easy for the non-expert.
Other types of thyroid function tests - such as measuring the level of T3 (tri-iodothyronine) and looking for thyroid peroxidase antibodies - may be helpful in certain circumstances.
For example, people who have autoimmune thyroid disease may present with ME/CFS-like symptoms. And a recent journal report described the disturbing case of an adolescent who had been misdiagnosed as having ME/CFS but turned out to have a severe autoimmune thyroiditis which required urgent treatment with steroids (ref: Lancet, 2003, 361, 572 - 'An organic cause of neuropsychiatric illness in adolescence'). But some of the other tests on offer in the private sector (e.g., the urine test) are highly speculative and not yet accepted by mainstream medicine here in the UK.
So if there's any doubt about thyroid status, it's worth asking for a referral to an endocrinologist (hormone expert) at a hospital.
At present, there is no reliable evidence to indicate that any type of thyroid disease is more common in people with ME/CFS although a few doctors (mainly in private practice) claim that this is the case.
Although there is an on-going debate in the medical journals about whether people can have defective thyroid function but normal thyroid function blood test results, I am not aware of any specialist or endocrinologist who supports the prescribing of thyroid supplements to people with normal test results. Consequently, NHS GPs and consultants are unlikely to agree with such an approach. This is a controversial form of treatment that is largely carried out in the private sector.
Thyroxine supplementation always has to be prescribed with great care and carefully monitored as this hormone stimulates activity in various parts of the body, in particular the heart. The problem is that even at very low doses some people are extremely sensitive to thyroxine supplementation and so develop potentially serious (even fatal) heart rhythm disturbances such as atrial fibrillation. There are also a number of potential long-term problems including suppression of the thyroid gland's natural output of thyroxine and increasing the risk of osteoporosis.
An additional potential problem in people with ME/CFS, who may already have low levels of the hormone cortisol, is that prescribing thyroxine in this situation can lead to additional stress on the adrenal glands and produce what is called an Addisonian crisis.
So before starting treatment with thyroxine (for whatever reason) people with ME/CFS ought have their cortisol level checked to make sure there is no significant degree of adrenal insufficiency (ref: BMJ, 1996, 313, 427 - 'Adrenal insufficiency should be excluded before thyroxine replacement is started').
Thyroid function is an area of medicine where more research is clearly needed and it would be worthwhile carrying out a proper research study to look at TSH, T4 and T3 levels in people with ME/CFS. In the meantime, many doctors will take the view that giving thyroid hormones to people with normal biochemical profiles remains dubious and potentially dangerous on both scientific and medicolegal grounds.
To follow up both sides of the debate in a little more detail, consult: BMJ, 1997, 314, 1764 - 'Thyroxine should be tried in clinically hypothyroid, but biochemically euthyroid patients' - the case in favor. BMJ, 1997, 315, 813-814 - responses from Professor Garth Williams ('Distinguishing hypothyroid symptoms from common non-specific complaints is difficult'); Professor A. Toft, President of British Thyroid Association (Giving thyroid hormones to clinically euthyroid but biochemically euthyroid patients'), and myself (Long term treatment is being used') - the case against. [There is public access to BMJ material: use the archive facility on their website at http://www.bmj.com
Source: This article was distributed via Co-Cure.