Flashcards in Case 9 Deck (42):
What are key history findings in an infant with congenital hypothyroidism?
Decreased feeding and activity, constipation, home delivery.
What are key physical findings in an infant with congenital hypothyroidism?
Large fontanelle, jaundice without bruising, umbilical hernia, no virilization, hypotonia without tremors or clonus
What is the differential diagnosis for congenital hypothyroidism?
Congenital adrenal hyperplasia, Congenital hypothyroidism, Down syndrome, Hypoglycemia, Sepsis, Shaken-baby syndrome, Hypoxic-ischemic encephalopathy
What are key lab findings in testing for congenital hypothyroidism?
Low free thyroxine (T4), High thyroid stimulating hormone (TSH)
Why is it important to detect congenital hypothyroidism so early?
If detected early on a newborn screen (when signs and symptoms usually are not yet present), early administration of thyroid hormone replacement prevents mental retardation.
The newborn screening system consists of five parts:
(1) Newborn testing
(2) Follow up of abnormal screening results to facilitate timely diagnostic testing and management
(3) Diagnostic testing
(4) Coordinating disease management with the medical home and genetic counseling
(5) Continuous evaluation and improvement of the newborn screening system
What are benefits of the newborn screening?
-Detect of a serious, treatable disorder before sx are present
-Institution of tx that can prevent serious problems
-Detection of carriers of certain genetic disorders
What are the risks of the newborn screening?
-Failure to identify some children who have the condition (false-negative result)
-Parental anxiety in cases of false-positive results
-Genetic test's revelation of misattributed paternity
-Detection of disorders for which treatment is not effective
What is the etiology of congenital hypothyroidism?
-Primary hypothyroidism - the most common type of CH In the US - results from some form of thyroid dysgenesis: Aplasia, hypoplasia, or an ectopic gland.
-Abnormalities at the level of the pituitary or hypothalamus (secondary or tertiary hypothyroidism) result in a low TSH and a low T4 and represent less than 4 percent of cases.
-An infant of a mother with autoimmune thyroiditis may have transient hypothyroidism
-An infant born to a mother with Grave's disease treated with antithyroid drugs may also have transient hypothyroidism
-Worldwide, iodine deficiency is the most common cause of hypothyroidism at birth
What is the epidemiology of congenital hypothyroidism?
-In the US, incidence is approx. 1:4000 live births (range 1:3600 - 1:5000) based on newborn screening data
-CH is more prevalent in the hispanic population (1 in 2,700) and Native Americans (1 in 700)
What signs and symptoms does congenital hypothyroidism present with?
-Usually not evident until after six weeks of age due to placental transmission of maternal thyroid hormone
-Early signs include feeding problems, decreased activity, constipation, prolonged jaundice, skin mottling, large fontanels, hypotonia, hypothermia, and umbilical hernia.
-Later signs include large tongue, hoarse cry, and puffy myxedematous facies.
Diagnosis of congenital hypothyroidism:
-Newborns with CH are now detected by the newborn screen
-Before newborn screening, approx. half of infants with CH were missed before 3 mo of age. Early detection and treatment can completely reverse the effects of fetal hypothyroidism in all but the most severe cases.
-Low thyroxine (T4) and elevated thyroid stimulating hormone (TSH) on the newborn screen must be confirmed with T4 and TSH measurements
-Because early tx is critical for normal development, infants should be started on levothyroxine (L-thyroxine) pending confirmatory lab results.
-If an infant presents with symptoms and physical findings suggestive of CH, the newborn screen should be sent, and specific tests for T4 and TSH should be obtained.
Weight gain in the breast fed baby:
Breastfed babies lose an average of 5.8 percent of their birth weight in the first few days of life.
Failure to regain birth weight by three weeks of age or continuous weight loss after 10 days of life has been defined as failure to thrive.
What should urine output be for a breastfed baby?
3-5 voids by 3-5 days of age. 4-6 voids by 5-7 days of age.
What should stool output be for a breastfed baby?
3-4 stools per day by 3-5 days of age. 3-6 stools by 5-7 days of age.
How are fontanels measured?
Fontanels are measured both by length (anterior-posterior dimension) and width (transverse dimension). One can then take the average of the length and width to determine a mean fontanel size and compare it to normal values.
What are large fontanels associated with?
-Skeletal disorders (eg rickets, osteogenesis imperfecta)
-Chromosomal abnormalities (eg Down syndrome)
-Other conditions (eg hypothyroidism, malnutrition, increased ICP, shaken baby syndrome)
What is premature closure or a small fontanel associated with?
Premature closure or a small fontanel for age may be a feature of microcephaly, craniosynostosis, hyperthyroidism, or a normal variant.
What is a sunken fontanel a sign of?
What is a bulging fontanel a sign of?
Generally a sign of increased intracranial pressure (eg, meningitis, hydrocephalus, subdural hematoma, lead poisoning)
What is lethargy defined as?
Defined as a level of consciousness characterized by poor or absent eye movements, or failure of a child to recognize parents or to interact with persons or objects in the environment.
The younger the child...
...the more difficult it is to assess lethargy.
A two-week-old child thought to be lethargic would have a differential diagnosis that includes but is not limited to:
-Infection (sepsis, meningitis)
-Intracranial pathology (hemorrhage from trauma, hydrocephalus, hydraencephaly)
What are the most likely differential diagnosis with congenital hypothyroidism?
CH, Down syndrome, congenital adrenal hyperplasia (CAH), Hypoglycemia.
What are less likely differential diagnosis with CH?
Sepsis, botulism, shaken baby syndrome, hypoxic-ischemic encephalopathy, polycythemia.
Congenital hypothyroidism (CH):
Due to maternal thyroid hormone, newborns appear normal, and an infant born with CH usually has no distinguishing features. If the condition is not detected by newborn screening, CH presents in the first two months of life with characteristic facies, enlarged and protruding tongue, a hoarse cry, and delayed growth and development. Constipation is common.
Typically hypotonic at brith and in the first months of life. May feed poorly. ROS otherwise normal.
Congenital adrenal hyperplasia (CAH):
Decreased feeding and activity are common in infants with CAH. Salt-losing CAH presents with irritability, lethargy, vomiting, and dehydration that can progress to shock. Many, but not all, states screen for CAH.
Clinical manifestations are variable and infants are frequently asymptomatic. Typical signs in a newborn include jitteriness, irritability, hypothermia, tremors, hypotonia, poor feeding and seizures.
Presents as an acute illness with fever.
Infants with botulism present with poor suck and weak cry. A rare diagnosis (about 900 cases reported worldwide) and usually presents a little later (median onset 3-4 mo of age).
Shaken baby syndrome:
Shaken baby syndrome with intracranial hemorrhage could present with decreased activity and poor feeding, but would be an acute presentation. A history of seizures or irritability would increase suspicion for this diagnosis. Hypotonia or hypertonia with a large fontanel may be seen in shaken baby syndrome. If bruising present, it would increase suspicion of non-accidental trauma, but absence of bruising does not rule it out.
Secondary to prenatal or perinatal central nervous system insult and usually presents shortly after birth. May present with lethargy and poor feeding. Often find evidence of multi-system dysfunction.
Occurs when the hematocrit is above the normal limit for gestational age (usually defined as greater than 65 percent in a term newborn). Many infants are asymptomatic, and hematocrits are not routinely checked. Associated symptoms include altered mental status, poor feeding, plethora (an excess of blood in the circulatory system or in one organ or area), acrocyanosis, and hyperbilirubinemia. Typically this condition occur in the first few hours to days of life.
T4 expected to be low and TSH elevated in CH.
Critical to check in any infant with hypotonia.
Serum sodium and potassium:
In a patient with CAH, low sodium and high potassium would be expected. Even though congenital adrenal hyperplasia (CAH) is very unlikely in the absence of virilization, serum sodium and potassium are reasonable to order to evaluation for this potentially life-threatening disorder.
Elevated in many inborn errors of metabolism, particularly urea cycle disorders (such as ornithine transcarbamylase deficiency), organic academias, and fatty acid oxidation disorders. Normal in congenital hypothyroidism.
Newborn metabolic screen:
Every infant born in the US should be screened shortly after birth using heel-stick blood spots to detect a variety of congenital conditions. Conditions included in newborn screening are congenital hypothyroidism, congenital adrenal hyperplasia, hemoglobinopathies (sickle cell disease), biotinidase deficiency, galactosemia, phenylketonuria, and cystic fibrosis.
How do you best manage congenital hypothyroidism?
1. Consultation with pediatric endocrinologist
2. Thyroid hormone replacement
3. Frequent follow up
4. Patient education
What is the goal of thyroid hormone replacement?
-The goal of tx with levothyroxine is to maintain TSH at approx. 1 mU/ml and T4 in the upper half of the normal range for age.
-Normalization of TSH by one to two months of age is associated with improved neurological outcome.