Answers Pediatric Neonatology MCQS Published on 24/8/2019

ANSWERS

MCQS#01

C. 11 beta-hydroxylase

Explanation:

11 beta-hydroxylase deficiency is the second most common cause of congenital adrenal hyperplasia, occurring particularly in individuals of Middle Eastern descent. It results from an inability to convert deoxycorticosterone to aldosterone and 11-deoxycortisol to cortisol. There is a resulting excess of 17 hydroxy-progesterone, which leads to increased serum androgen production. There is no salt-wasting because deoxycorticosterone acts as a mineralocorticoid. Male infants have normal external genitalia at birth while females may have ambiguous genitalia of variable severity because of increased androgen exposure. Diagnosis is confirmed with increased deoxycorticosterone

and deoxycortisol concentrations. Therapy includes glucocorticoid replacement and genital reconstruction.

References:

Brodsky D, Martin C. Neonatology Review. 2nd edition. Lulu. 2010

Kliegman RM, Behrman RE, Jenson HB, Stanton B (eds). Nelson Textbook of Pediatrics. 18th edition. Philadelphia: Saunders, 2007.

MCQS#02

C. Transposition of the great vessels

Explanation:

Effects of maternal diabetes on the fetus are well-known and include congenital heart disease (hypertrophic cardiomyopathy, ventricular septal defect, transposition of the great vessels), renal anomalies, caudal regression, neural tube defects, central nervous system anomalies, and small left colon. The risk of congenital malformations correlates with the degree of uncontrolled maternal diabetes. If a woman with diabetes achieves glycemic control after conception, the risk of fetal anomalies is 7.8%; however, if glycemic control is attained prior to pregnancy, the risk of fetal anomalies decreases to 2.5%.

Reference: Brodsky D, Martin C. Neonatology Review. 2nd edition. Lulu. 2010.

MCQS#03

D. Thyroid dysgenesis

Explanation:

Congenital hypothyroidism can present with prolonged jaundice, a large posterior fontanel, umbilical hernia, macroglossia, hoarse cry, abdominal distention, hypotonia, feeding difficulties, lethargy, mottled skin, hypothermia, and goiter. Long-term consequences include delayed growth, cognitive deficits, and delayed puberty. The most common etiology of congenital hypothyroidism is

thyroid dysgenesis (occurring in ~75% of cases), which results from partial or complete absence of the thyroid gland.

Thyroid dyshormonogenesis occurs in ~10% of infants with congenital hypothyroidism and leads to inadequate thyroid hormone production. It can be caused by thyroid-stimulating hormone resistance, defects in iodide transport, thyroglobulin abnormality, deiodase deficiency, or an organification defect.

Defects in the hypothalamic-pituitary axis, such as panhypopituitarism, are much less common, occurring in ~5% of individuals affected by congenital hypothyroidism. It is associated with other hormone deficiencies.

Neonatal hypothyroidism can also be caused by transient hypothyroidism (~10%), which is attributable to maternal medications, maternal antibodies, or neonatal iodine exposure. Preterm infants commonly have transient hypothyroxinemia of prematurity of unknown etiology but may be related to an immature hypothalamic-pituitary axis. Sick euthyroid presents as temporarily low thyroid hormone levels with normal thyroid-stimulating hormone in the setting of an acute or chronic illness.

References:

Belfort MB, Brown RS. Hypothyroidism in the preterm infants. In: Primary Care of the Premature Infant. Brodsky D, Ouellette MA (eds). Philadelphia: WB Saunders, 2008.

Brodsky D, Martin C. Neonatology Review. 2nd edition. Lulu. 2010.

Grasberger H, Refetoff S. Genetic causes of congenital hypothyroidism due to dyshormonogenesis. Curr Opin Pediatr. 2011;23:421-428.

MCQS#04

B. Decrease in serum osmolality and increase in urine osmolality

Explanation:

The infant in this vignette likely has neurogenic or central diabetes insipidus (DI) caused by a decrease in anti-diuretic hormone (ADH) production as a result of his intracerebral hemorrhage. Other intracranial lesions, such as tumors and arterio-venous malformations, can also lead to central DI. About 10% of cases are idiopathic. The inadequate ADH production causes free water loss from the kidney resulting in hypernatremia, an increase in serum osmolality, and inappropriately dilute urine. Treatment with exogenous ADH will lead to a decrease in serum osmolality and an increase in urine osmolality.

In contrast to central DI, individuals affected by nephrogenic DI have an inadequate renal response to ADH. Similar to central DI, the disease is associated with increased serum osmolality and decreased urine osmolality. However, serum ADH levels are normal or elevated. After administration of exogenous ADH, serum and urine osmolalities are not altered.

References:

Kliegman RM, Behrman RE, Jenson HB, Stanton B (eds). Nelson Textbook of Pediatrics. 18th edition. Philadelphia: Saunders, 2007.

Knoers N. Nephrogenic diabetes insipidus. In: GeneReviews. Pagon RA, Bird TD, Dolan CR, Stephens K (eds). Seattle (WA): University of Washington, Seattle, 2010.

Porterfield SP. Endocrine Physiology. 2nd edition. St Louis: Mosby; 2001.

MCQS#05

D. Hypocalcemia

Explanation:

Maternal diabetes can lead to neonatal hypocalcemia, hypoglycemia and hypomagnesemia. Although jitteriness most commonly reflects hypoglycemia in an infant of a diabetic mother, the infant in this vignette has a normal glucose concentration, heightening suspicion for another electrolyte problem. Although infants with hypocalcemia and hypomagnesemia may be asymptomatic, both can induce jitteriness. Classic signs of hypocalcemia include Chvostek and Trousseau signs, irritability, laryngospasm, tetany, seizures, and prolonged QT interval. Infants with hypomagnesemia may have muscle weakness, increased deep tendon reflexes, irritability, jitteriness, seizures, and a prolonged QT interval. Hypocalcemia and hypomagnesemia are both treated with careful monitoring and replacement of the deficient electrolyte.

Reference:

Kliegman RM, Behrman RE, Jenson HB, Stanton B (eds). Nelson Textbook of Pediatrics. 18th edition. Philadelphia: Saunders, 2007.