Transcript disoders of thyroid gland

DISODERS OF THYROID
GLAND
Ass.prof. of hospital pediatrics
department
HYPOTHYROIDISM
Hypothyroidism
results
from
deficient
production of thyroid hormone or a defect in
its receptor. The disorder may be manifest
from birth. When symptoms appear after a
period of apparently normal thyroid function,
the disorder may be truly "acquired" or may
only appear so as a result of one of a variety of
congenital defects in which the manifestation
of the deficiency is delayed. The term
cretinism is often used synonymously with
congenital hypothyroidism but should be
avoided
CONGENITAL HYPOTHYROIDISM
Congenital causes of hypothyroidism
may be sporadic or familial, goitrous or
nongoitrous. In many cases, the
deficiency of thyroid hormone is severe,
and symptoms develop in the early
weeks of life. In others, lesser degrees
of deficiency occur, and manifestations
may be delayed for months or years.
TREATMENT. Sodium-L-thyroxine given orally is the treatment of choice.
Because 80% of circulating T3 is formed by monodeiodination of T4,
serum levels of T4 and T3 in treated infants return to normal. This is also
true in the brain, where 80% of required T3 is produced locally from T4. In
neonates, the dose is 10–15 m{mu}g/kg (37.5 or 50 m{mu}g/24 hr). Levels
of T4 and TSH should be monitored and maintained in the normal range.
Children with hypothyroidism require about 4 m{mu}g/kg/24 hr, and adults
require only 2 m{mu}g/kg/24 hr.
Later, confirmation of the diagnosis may be necessary for some infants to
rule out the possibility of transient hypothyroidism. This is unnecessary
in infants with proven thyroid ectopia or in those who manifest elevated
levels of TSH after 6–12 mo of therapy owing to poor compliance or an
inadequate dose of T4. Discontinuation of therapy at about 3 yr of age for
3–4 wk results in a marked increase in TSH levels in children with
permanent hypothyroidism.
The only untoward effects of sodium-L-thyroxine are related to its dose.
An occasional older child (8–13 yr) with acquired hypothyroidism may
develop pseudotumor cerebri within the first 4 mo of treatment. In older
children, after catch-up growth is complete, the growth rate provides an
excellent index of the adequacy of therapy. Parents should be forewarned
about changes in behavior and activity expected with therapy, and special
attention must be given to any developmental or neurologic deficits.
THYROIDITIS
LYMPHOCYTIC THYROIDITIS
(Hashimoto Thyroiditis; Autoimmune Thyroiditis)
Lymphocytic thyroiditis is the most common cause of
thyroid disease in children and adolescents and accounts
for many of the enlarged thyroids formerly designated
"adolescent" or "simple" goiter. It is also the most common
cause of acquired hypothyroidism, with or without goiter. Its
incidence may be as high as 1% among school children.
ETIOLOGY. This is a typical organ-specific autoimmune
disease. The condition is characterized histologically by
lymphocytic infiltration of the thyroid. Early in the course of
the disease, there may be only hyperplasia; this is followed
by infiltration of lymphocytes and plasma cells between the
follicles and by atrophy of the follicles. Lymphoid follicle
formation with germinal centers is almost always present;
the degree of atrophy and of fibrosis of the follicles varies
from mild to moderate.
Familial clusters of lymphocytic thyroiditis are common; the
incidence in siblings or parents of affected children may be
as high as 25%. Autoantibodies to thyroglobulin (Tg) and
human thyroid peroxidase (hTPO) in these families appear to
be inherited in an autosomal dominant fashion, with reduced
penetrance in males. The concurrence within families of
patients
with
lymphocytic
thyroiditis,
"idiopathic"
hypothyroidism, and Graves disease provides cogent
evidence for a basic relationship among these three
conditions. The disorder has been associated with many of
the other autoimmune disorders more often than would be
expected by chance alone. Autoimmune thyroiditis occurs in
10% of patients with type I polyglandular autoimmune
syndrome, which consists of hypoparathyroidism, Addison
disease, and mucocutaneous candidiasis. The association of
Addison disease with insulin-dependent diabetes mellitus or
autoimmune thyroid disease or both is known as Schmidt
syndrome or type II polyglandular autoimmune disease.
Autoimmune thyroid disease also tends to be
associated with pernicious anemia, vitiligo, or
alopecia. TPOAb are found in approximately 20% of
white and 4% of black children with diabetes mellitus.
Autoimmune thyroid disease has an increased
incidence in children with congenital rubella.
Lymphocytic thyroiditis is also associated with certain
chromosomal
aberrations,
particularly
Turner
syndrome and Down syndrome. The pathogenetic
mechanisms for these associations are not known.