HYPOTHYROIDISM IN CHILDHOOD
The thyroid gland lies at the front of the neck wrapped around the windpipe
and produces a hormone (a chemical secreted into the blood that controls
the function of other organs) called thyroxine. This substance has profound
effects on all the organ systems of the body by controlling the rate of
their essential chemical processes. Inadequate secretion of thyroxine can
occur at any age and is called hypothyroidism (or myxoedema). In childhood
it may be congenital (present at birth) or 'acquired' (occurring later).
As the symptoms are initially mild and of gradual onset, the diagnosis
is often delayed but fortunately the treatment is simple and fully effective.
Incidence:
Congenital hypothyroidism occurs in about 1 child in 3,500 and is now
picked up by screening all newborn babies. A similar number of children
develop hypothyroidism later in childhood and the diagnosis has to be made
clinically.
Cause:
Hypothyroidism in childhood is usually due to an 'autoimmune' process
in which, triggered by unknown factors (possibly viruses), antibodies are
formed against the cells of the thyroid gland and gradually destroy its
function. The gland may enlarge and become obviously visible in the neck
or it may shrink. There are other causes of hypothyroidism in childhood
but these are rare.
Symptoms:
In childhood thyroxine has an important role in the control of growth
and the most fundamental sign of thyroid underactivity is slowing of the
rate of growth but this becomes obvious only when hypothyroidism is profound.
It is often assumed that children with hypothyroidism will do badly at
school but paradoxically they generally do well, possibly because slowing
children down a little improves their concentration! The classical changes
of adult hypothyroidism which include dryness of the skin and hair, coarsening
of the facial features, constipation and a slow pulse rate all occur in
children but tend to be late features.
Diagnosis:
Once suspected the condition is easily confirmed by measurement in the
blood of thyroxine and thyroid stimulating hormone (TSH, a hormone from
the pituitary gland in the head which 'drives' the thyroid).
Treatment:
Thyroxine is available as pills containing either 25, 50 or 100 microgrammes
(usually writtten ug) of the pure substance. The dose in children is closely
related to size and varies from 25 to 200ug daily. The adequacy of the
dose is checked by measurement of thyroxine and TSH in the blood from time
to time. Fortunately the thyroxine in the body forms a 'pool' of hormone
from which more active hormones are made so an exact dose is not necessary.
For the same reason an occasional missed dose does not matter but it is
important to establish a good system for remembering the dose because frequent
missed pills do of course result in a return of symptoms.
Outlook:
Thyroxine by mouth replaces the natural hormone and so provides perfect
treatment. The child or adult with hypothyroidism is restored to full health
in all respects. There is rapid catch up in growth and development and
all previous symptoms resolve. Puberty progresses normally and adult reproductive
function is normal. There are often some concerns during the return to
normal thyroid function in children. The change in personality and energy
may be dramatic and for a while behaviour and school performance may deteriorate
sharply. Parents and teachers may be alarmed to find themselves dealing
with a completely 'new' child. Other concerns may include aching of the
joints and some loss of hair, never enough to become a cosmetic problem.
All these problems are transient and the child is soon fully well. No activities
are barred, no illness poses a special threat and no other treatment which
may be needed is incompatible with thyroxine. The thyroxine needs to be
taken lifelong. The condition does tend to run in families so there is
an appreciable risk that other family members may develop thyroid disorders
(either under- or over-activity) in the future. |
