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CONGENITAL HYPOTHYROIDISM
General Hospital of Tianjing Medicine University
Introduction
Congenital hypothyroidism results from deficient production of thyroid hormone or a defect of thyroid hormonal receptor activity. The disorder may be manifested from birth. The major clinical characteristics of congenital hypothyroidism are retardation in growth and mental development.
Introduction
Congenital hypothyroidism
sporadic endemic
Etiology
Thyroid dysgenesis
Development defects (thyroid dysgenesis) account for 90% of infants in whom hypothyroidism is detected.
Aplasia In about one third, even sensitive radionuclide scans can find no remnants of thyroid tissue .
Ectopia In the other two thirds of infants, rudiments of thyroid tissue are found in an ectopic location ,such as lingual thyroid .
Defective synthesis of thyroxin
• A variety of defects in the biosynthesis of thyroid hormone (for example, enzyme deficiency) may result in congenital hypothyroidism. A goiter is almost always present in these patients. These defects are transmitted in an autosomal recessive manner.
Thyrotropin deficiency
• multiple hormones deficiency of pituitary or hypothalamus
• Hypothyriodism is one of many symptoms
• There are accompanied by hypoglycemia, and other Clinical manifestations
Thyroid gland or peripheral target organ unresponsiveness (receptor disorder)
thyroid tissue does not response to TSH
peripheral tissue does not respond to T4
and T3
Biosynthesis of thyroid hormones
The major materials
for synthesis of
thyroid hormone
tyrosine
iodine
Biosynthesis of thyroid hormones
Trapping of iodide Thyroid follicular cells have an active iodide pump, which can
concentrate iodide against a steep concentration gradient,iodide is transported from the blood into the thyroid.
Iodide oxidized Iodide first be oxidized . This reaction is catalyzed by thyroid
peroxidase.
Tyrosine iodination Iodination of tyrosine forms monoiodotyrosine (MIT)
and diiodotyrosine (DIT) bound in the thyroglobulin.
Biosynthesis of thyroid hormones
Iodotyrosine condensation (coupling) 2 DIT →T4, 1 DIT+1 MIT→T3 (coupling enzyme ) T4 or T3 are stored as thyroglobulin in the lumen of the follicle until that time when the hormone is to be secreted into th
e bloodstream (proteolytic enzymes ) and then delivered to the body cells.
thyroxine-binding globulin (TBG) is the most important plasma proteins which transport thyroid hormone
Regulation of thyroid function
The thyroid is regulated by thyroid-stimulating hormone (TSH) which is secreted by the anterior pituitary. TSH synthesis and release are stimulated by TSH –releasing hormone (TRH), which is synthesized in the hypothalamus and secreted into the hypophyseal portal which enters the pituitary. In a state of decreased production of thyroid hormone, TSH and TRH are increased. Exogenous thyroid hormone or increased thyroid hormone synthesis causing elevated blood levels inhibits TSH and TRH production. This is called negative feedback. (see Fig)
Action of thyroid hormones
Growth and development Nervous system
development increase DNA concentration in the nervous
system and the number of neurons . promote maturation of the nervous system .
Metabolism
promotes heat production
increases glucose absorption
Increases blood cholesterol
accelerates both synthesis and
degradation of protein.
Incidence
Europe and American: 1 in 4,000
1 in 5000-7000 in China
Clinical manifestations
• Congenital hypothyroidism is twice as common in girls as in boys.
• The severity of the findings in cases of thyroid deficiency depends on the degree of deficiency of production of thyroid hormone.
• Most infants with congenital hypothyroidism are asymptomatic at birth even if there is complete agenesis of the thyroid gland.
• This situation is attributed to the transplacental passage of moderate amounts of maternal thyroxine, which provides fetal levels that are 25-50% of normal at birth.
• these low serum levels of T4 and concomitantly elevated levels of thyroid-stimulating hormone (TSH) make it possible to screen and detect most hypothyriod neonatales.
Clinical manifestations
Neonatal The signs and symptoms are usually not sufficiently developed in the newborn.
Birth weight and length are normal,but head size may be slightly increased because of myxedema of the brain.
Prolongation of physiologic icterus may be theearliest sign Feeding difficulties , hoarse voice or cry .Skin may be dry, coarse and mottled; hypothermia Decreased stooling or constipation
Clinical manifestations
Umbilical hernia
Characteristics of typical hypothyroidism
Physiological hypofunction.
Hypothermia; bradycardia ;diminished
sweating ;hoarse voice or cry ;poor
appetite
sometimes constipation
Clinical manifestations
Retardation of growth and development
Clinical manifestations
short stature Delays in formation and eruption of teeth may occur
short stature
Delay in central nervous system development
Clinical manifestations
Thyroid hormone deficiency presented from birth leads to marked delay in central nervous system development.
Hypothyroid infants appear lethargic and are late in learning to sit, stand and talk
the mental retardation becomes irreversible if treatment is delayed
Characteristic facies.
Clinical manifestations
The skin may be dry, thick, and scaly
eyes appear far apart; bridge of the nose is depressed palpebral fissures are narrow and eyelids swollen. The mouth is kept open, and the thick and broad tongue protrudes from it
Coarse facial features
Laboratory findings
Early diagnosis is very important
Therefore neonatal screening programs is of first importance.
assay serum T4 and TSH or TSH alone.
serum T4 values are very low and TSH concentrations high in a newborn with primary hypothyroidism.
Filter blood spots
(blood of heel )
Laboratory findings
Serum T3, T4, TSH.
T4 TSH
Skeletal X-ray (bone age). Epiphysis development (bone age) is delayed.
Scanning (radioisotope using 99mTC(technetium, a element)) of the thyroid gland.
determine morphological development and function of thyroid.
radionuclide scans
Normal thyroid
Thyriod under tongue and displasia
Diagnosis
A.Growth Retardation, diminished physical activity, impaired tissue perfusion, constipation, thick tongue, poor muscle tone, hoarseness, anemia; intellectual retardation if the hypothyroid infant is untreated.
B. Delayed dental and skeletal maturation
C. Thyroid functions studies to show low T4; TSH levels elevated
Note: The importance of the newborn screening procedure must be underscored.
Differential diagnosis
• Rickets
• Down `s syndrome
• Pituitary dwarfism (Growth hormone deficiency)
• Congenital giant colon
mental is normal.
Bone age is normal.
Skeletal X –ray
No characteristic facies
Serum levels of T4 and TSH are normal.
Rickets
Down `s syndrome
Chromosome abnormalityMental retardation No myxedema Characteristic facies.
Pituitary dwarfism (Growth hormone deficiency)
Short stature
Bone age is delayed
Intelligence is usually normal
No characteristic facies or physiological hypofunction.
Congenital giant colon
Distention and constipationno other manifestation of congenital hypothyroidism
Treatment
• Principle : 1 Treatment of hypothyroidism requires exogenous thyroid
hormone 2 Treatment of entire life 3 In order to maintain normal physiological functions. Serum T4, TSH and the condition of growth and development should be periodically measured
during treatment. 4 Dosage should be adjusted according to the concentration of serum T4, TSH and the states of growth and development.
Treatment
Dry thyroid
Preparation (drug):
Sodium-L thyroxine
a dried and powdered preparation of porcine or bovine thyroid gland.
Synthetic levothyroxine L-T4
treatment:
• Method of treatment: start dose(L-T4):infant is 8-14 ug/kg; child is 4ug/kg. Every one to two weeks a dosage are added ,until clin
ical symptoms improve , T4 and TSH return to normal ,then a constant dosage are given
• Follow up: One to two weeks are needed initially; every 3 mont
hs after dosage stability; every a half of year follow up after 1-2 years.
Prognosis
Early diagnosis and adequate treatment from the first weeks of life may result in normal linear growth and intelligence.
Delay in diagnosis, inadequate treatment, result in variable degrees of brain damage.
Without treatment, affected infants may become mentally deficient dwarfs.
An infant of 6 mo. A before treatment B four mo after treatment
Key point
1 Main types of Congenital hypothyroidism 2 Etiology :thyroid dysgenesis (aplasia,ectopia );defective synthesis ;thyrotropin deficiency;thyroid gland or peripheral target organ unresponsiveness3 Neonatal earliest sign may be prolongation of physiologic icterus4 Characteristic of typical hypothyroidism(main)5 Early diagnosis is very important and neonatal screening programs is of first im
portance6 Essentials of diagnosis 7 Principle of treatment 8 Definition of congenital hypothyroidism