GRAVES' DISEASE (hyperthyroidism, thyrotoxicosis) IN CHILDHOOD
Cause.
Overactivity of the thyroid gland is rare in childhood but increases
in frequency into young adult life, affecting girls more than boys. It
is nearly always due to Graves' disease, now recognised to be an "autoimmune"
condition, in which antibodies (proteins circulating in the blood whose
usual function is to protect against infection) react with the body's own
organs causing damage or, in this condition, stimulation. The cause is
not known but it is clear that some people are genetically more susceptible
than others and it is probable that a virus infection may act as the final
trigger. Similar antibodies may cause underactivity of the thyroid (sometimes
called Hashimoto's disease) and both conditions often occur in the same
families.
Symptoms.
The overstimulated thyroid gland produces too much of the hormone (a
circulating chemical compound that affects distant cells) thyroxine which
in turn has the effect of accelerating the chemical processes in most of
the cells of the body. The affected child becomes progressively more anxious,
nervous and restless with disturbed sleep (usually with nightmares), deteriorating
school performance (especially the handwriting), racing pulse even in sleep,
increased appetite and yet there is usually weight loss, excessive sweating,
tremor and diarrhoea. Because the onset of the symptoms is gradual and
the pattern is variable, psychological disturbance is often suspected before
the true problem is identified. The thyroid gland in the front of the neck
becomes enlarged, but this may not be at all obvious. In only a minority
of children do the eyes become prominent (exopthalmos, proptosis) but this
can be a major feature of the disease.
Diagnosis.
Once suspected, hyperthyroidism is easily confirmed by checking the
thyroxine (and the thyroid stimulating hormone) levels in the blood.
Treatment.
There are three methods of treatment available:
1. Drugs.
Two major drugs are effective in reducing the secretion of thyroxine,
carbimazole (Neomercazole, most commonly used in the UK) and propylthiouracil.
Both are generally well tolerated but can produce side effects in about
5% of children; these are usually just skin rashes but severe effects on
blood cells have very rarely occurred. For this reason if any acute infection
occurs in a child on treatment, the blood count should be checked.
2. Surgery.
The thyroid gland can be subtotally removed. This is a major operation
which inevitably leaves a visible scar and can rarely cause damage to the
nerves controlling the larynx or to the parathyroid glands which lie just
behind the thyroid. Since it is not possible to judge exactly how much
gland to remove there can be recurrence of thyroxicosis or thyroid underactivity
can occur after surgery.
3. Radioiodine.
A radioactive isotope of iodine (131I) can be given by mouth in a watery
solution which is then concentrated by the thyroid gland and gradually
destroys the secreting cells. This form of treatment is simple and has
an excellent safety record (after more than 40 year's use) but it does
inevitably destroy the function of the gland so thyroid underactivity (hypothyroidism)
develops and lifelong thyroxine replacement is needed.
Outlook.
For children we generally recommend a course of treatment with carbimazole
to control the thyroid overactivity (once control is established thyroxine
is added and both are given together since in this way it is simpler to
maintain the correct balance). If it is well tolerated drug treatment is
usually continued for 18 months to two years because there is a reasonable
chance (about 25%) that the disease may recover spontaneously within that
time. If hyperthyroidism recurs when the treatment is stopped, drug treatment
can be resumed for a further period but we favour treatment with radioiodine
in most children because of its safety, simplicity and effectiveness. After
such treatment the thyroid gland is destroyed but replacement treatment
with thyroxine is simple and completely effective and no futher medical
attention is needed for the problem. |
