Congenital Hypothyroidism- Neonatal Screening
Swati Gadewar (Kolpuru)
Consultant Pediatrician, USA
First Created: 12/12/2001 

Introduction

Congenital hypothyroidism is one of the preventable causes of mental retardation if diagnosed within the first 3 months of life. Major complications can be prevented if diagnosed early and started on replacement therapy. Early diagnosis is difficult because the clinical signs are not apparent at birth and appear gradually. Thus it is very important to screen newborns for congenital hypothyroidism and it is a routine newborn screening test in most of the developed countries.

Causes Of Congenital Hypothyroidism

Thyroid agenesis or dysgenesis

  • Ectopic thyroid gland
  • Defective synthesis
  • TRH deficiency or insensitivity
  • TSH deficiency or insensitivity
  • Transplacental passage of antithyroid drug
  • Peripheral resistance to thyroid hormone.
  • Maternal ingestion of goitrogens

Congenital Hypothyroidism - Clinical Manifestations

The clinical manifestations depend on the functional state of the thyroid. They are generally absent at birth and appear gradually over about 6 weeks.

Early manifestations:

  • Lethargy
  • Poor feeding
  • Inactivity
  • Respiratory distress
  • Hypotonia
  • Large anterior and posterior fontanelles
  • Pallor
  • Peripheral cyanosis
  • Hoarse cry
  • Constipation
  • Hypothermia
  • Prolonged physiologic jaundice

Late manifestationsLate manifestations:

  • Depressed nasal bridge
  • Narrow forehead
  • Puffy eyelids
  • Thick, dry and coarse skin
  • Coarse hair
  • Large tongue
  • Abdominal distension
  • Umbilical hernia
  • Poor reflexes
  • Bradycardia
  • Hypotension
  • Pot belly
  • Diminished pulse pressure
  • Anemia not responding to iron
  • Sensorineural hearing loss
  • Slipped capital femoral epiphysis can occur
  • Kocher-Debre-Semelaign syndrome, which consists of generalized muscular hypertrophy giving the child a "Herculean" appearance.
  • Growth retardation
  • Mental retardation
  • Delayed sexual maturation

Ancillary laboratory manifestations:

  • Delayed bone age
  • Epiphyseal dysgenesis
  • Low complexes in the EEG and ECG
  • Cardiomegaly on X-ray chest indicating myxedema
  • Enlargement of sella turcica

Investigations

Screening Methods

Specimens are obtained by a heel stick filter-paper blood spot. The results are more reliable if the TSH test is done on day 5 of life and the T4 test between days 2 and 5 of life. There is a physiologic increase in T4 levels at 2-5 days of life, which is not seen, in hypothyroid infants.

T4 and sequential TSH measurement:
Most North American programs use this method. First, a filter paper blood test for T4 is done. All with low T4 values a TSH measurement is done.

Advantages: Detects neonates with:

  • rimary hypothyroidism which has low T4 and high TSH

  • Thyroxine binding globulin deficiency with low T4 and a low TSH. TBG concentration measurement should be done in such cases.

  • Hypothalamopituitary hypothyroidism, which has low T4 and normal TSH.

  • Can detect secondary and tertiary hypothyroidism, which cannot be detected by TSH screening alone.

  • Detects most cases of compensated hypothyroidism.

  • Cheaper

Limitations:

  • Fails to detect infants with normal T4 and elevated TSH.

  • High false positive results because T4 levels are affected by changes in the concentration of TBG. False positive results are seen in preterm and stressed infants.

TSH and sequential T4 measurement TSH and sequential T4 measurement:
Most laboratories in Europe use this method. TSH is measured in all newborns and it is followed by T4 in cases with high TSH values. This method is used when the detection of primary hypothyroidism is the major goal.

Advantages:

  • Less variable results resulting in fewer false-positive cases.

Limitations: This method will miss cases with:

  • Thyroxine-binding globulin deficiency

  • Hypothalamo-pituitary hypothyroidism

The diagnosis of congenital hypothyroidism must be confirmed by the measurement of serum T4 and TSH concentrations at 2-6 weeks of life.


Congenital Hypothyroidism- Neonatal Screening Congenital Hypothyroidism- Neonatal Screening 12/12/2001
Disclaimer: The information given by www.pediatriconcall.com is provided by medical and paramedical & Health providers voluntarily for display & is meant only for informational purpose. The site does not guarantee the accuracy or authenticity of the information. Use of any information is solely at the user's own risk. The appearance of advertisement or product information in the various section in the website does not constitute an endorsement or approval by Pediatric Oncall of the quality or value of the said product or of claims made by its manufacturer.
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0