| Graves'
Hyperthyroidism (Thyrotoxicosis) |
Index to this Health
Guide
Graves
Disease
Thyroid Stimulating Antibody
Clinical Features
Treatment
Radioactive Iodine
Antithyroid Drugs
Thyroidectomy
Other Causes of Hyperthyroidism
|
Health
Guides on Thyroid Disease
|
|
Graves'
Disease
Graves' disease is
named after the Irish physician who described several cases in
the London Medical Journal in 1835. It was actually first described
by Parry a few years earlier. In Europe the disease is known as
Basedow's disease. In all countries it is also known as "thyrotoxicosis".
Graves' disease, by far the most common cause of hyperthyroidism
in Canada, affects perhaps one in every 100 people. It appears
to be becoming even more common. The disease is an inherited disorder,
although not every member of the afflicted families will suffer
this condition. It is more common in females than in males.
|
|
Thyroid
Stimulating Antibody
Graves' disease is
an autoimmune disorder. It is caused by an abnormal protein, called
thyroid stimulating antibody. This antibody stimulates the thyroid
gland to produce large amounts of thyroid hormone in an uncontrolled
manner. In normal people, the production of thyroid stimulating
antibody (and other abnormal antibodies) is prevented by a surveillance
system. This system consists of certain blood cells called suppressor
and helper lymphocytes and Killer (K) cells, as well as other
constituents. The suppressor lymphocytes suppress unwanted lymphocytes.
Measurement of the
thyroid stimulating antibody present in the blood of most patients
with Graves' disease is not usually necessary, in order to establish
the diagnosis.
|
|
Clinical
Features
The symptoms and signs
of Graves' hyperthyroidism are due to the effects of excess amounts
of thyroid hormone on body function and metabolism. Common symptoms
include weight loss, nervousness, irritability, intolerance to
hot weather, excessive sweating, shakiness, and muscle weakness.
Other signs include a rapid pulse, loss of body fat and muscle
bulk, thyroid enlargement (goitre), fine tremors of the fingers
and hot, moist, velvety skin.
About 50% of patients
also have significant eye signs (Ophthalmopathy). The eyes, which
bulge from their sockets are red and watery and the lids are swollen.
Quite often the eyes do not move normally because the swollen
eye muscles are unable to work precisely. The remaining 50% of
patients with Graves' hyperthyroidism may have slightly bulging
eyes because of spasm of the muscle of the lids, giving them a
staring appearance.
Thyroid hormones have
a wide variety of effects on the body and the symptoms and signs
reflect these. In simple terms, all the metabolic processes are
"speeded up"; for example, the pulse rate is rapid (over 100),
bowel function is increased (diarrhea), and the sweat glands work
excessively. The nervous system is also stimulated so that the
patient becomes irritable and nervous. Despite increased appetite,
the patient usually loses weight because food intake cannot keep
up with the increased breakdown of body proteins. The end result
is a thin, hot, nervous patient with "poppy" eyes and a goitre
- a classical clinical situation quickly recognized by any medical
practitioner who has previously seen such a patient.
Top
|
Treatment
Because Graves' hyperthyroidism
is caused by a genetically determined abnormality of the immune
system, the problem is complex and there is at present no specific
treatment for the underlying abnormality. Since the end result of
this problem is an overstimulation of thyroid function, treatment
of the symptoms is quite easy - one can either surgically remove
part of the thyroid gland (thyroidectomy), destroy the thyroid cells
with radioactive iodine, or block thyroid hormone production with
antithyroid drugs.
|
Radioactive
Iodine
Although radioactive
iodine is by far the simplest and most convenient treatment, its
use in younger adults and children has previously been a matter
of concern because of the possible harmful effects of radiation.
Radioactive iodine has been used for over 40 years and there is
no good evidence of any harmful effects. Most thyroid specialists
would recommend its use in all patients with Graves' disease over
the age of 20-25; some would use it in children as well. However
it occasionally aggravates the eye signs.
Radioactive iodine is
usually given in the form of a capsule. The dose is calculated from
the size of the goitre by performing a "Thyroid Uptake Test." Because
radioactive iodine takes several weeks to take its full effect,
antithyroid tablets are also sometimes given until such time as
the full effect occurs. More often than not, patients end up hypothyroid
due to the radioactive iodine, and have to take thyroxine for life.
|
Antithyroid
Drugs
Antithyroid drugs (of
which Propylthiouracil and Methimazole are the only ones available
in Canada) are almost mandatory in children and adults under the
age of 20-25. It may also be used at any age so as to bring about
remissions, or prior to ablation therapy. There are two main drawbacks
with this type of treatment:
- patients must take tablets for
many months or years;
- once treatment is stopped, there
is only about a 50% chance that the disease will not flare up
again.
In addition a very small percentage
suffer side effects which very rarely can be severe. Eventually,
most patients require treatment with either radioactive iodine or
thyroidectomy. Another tablet that can be given to treat the symptoms
of hyperthyroidism is Propranolol. This drug blocks the effects
of excess thyroid hormones on the heart, blood vessels, and nervous
system, but has no direct effect on the thyroid gland.
|
Thyroidectomy
Surgery is sometimes recommended
for the 80% of patients under the age 20 who have a recurrence of
hyperthyroidism after antithyroid drugs. Thyroidectomy is also recommended
for patients of any age in whom the goitre is so big that it causes
blockage of the windpipe (trachea) or food passage (esophagus).
In England and Europe, thyroidectomy is performed for Graves' disease
much more often than in Canada, largely because of experience and
tradition. Thyroidectomy requires admission to hospital for about
5 days and removal (by an experienced surgeon) of all but a small
portion of the gland.
After treatment with radioactive
iodine or thyroidectomy, it is hoped that enough of the thyroid
gland remains to function normally. Occasionally, the gland becomes
overactive again since the abnormal stimulating antibody is still
being produced by the lymphocytes. In other patients, there is a
strong tendency for the remaining thyroid gland to become underactive
(hypothyroidism) - perhaps 80% of all patients with Graves' disease
will eventually require lifelong thyroid hormone replacement therapy.
This is not considered a problem as long as the hypothyroidism is
recognized and treated. It is much more of a problem for patients
to have a recurrence of hyperthyroidism because of failure to remove
enough gland or if too small dose of radioactive iodine is given.
Indeed, some specialists deliberately destroy the thyroid in order
to prevent a recurrence of the hyperthyroidism, and immediately
treat with thyroid hormone in anticipation of hypothyroidism.
|
Other
Causes of Hyperthyroidism
In Canada, Graves' disease accounts
for at least 90% of all patients with hyperthyroidism. Hyperthyroidism
can also occur in older patients with long-standing nodular goitres.
Other uncommon causes of hyperthyroidism
in Canada are painful (subacute) thyroiditis caused by a viral infection
of the thyroid gland in which the hyperthyroidism is due to leakage
of thyroid hormones from the swollen, damaged gland and "silent"
thyroiditis, a similar condition but without the painful swelling
of the thyroid. Multinodular or single nodular goitres may become
autonomous and produce hyperthyroidism. A few other rare causes
of hyperthyroidism need not be discussed here.
Top
|
A
printed version of this Health Guide is available to health care
professionals and the public. For more information call the National
Office or contact your local
chapter.
Production of
the printed version of this Health Guide was made possible through
partial funding assistance from Health Canada. The views expressed
herein are solely those of the authors and do not necessarily represent
the official policy of Health Canada. |
|
