A 12-week-old female infant is brought to the office by her mother due to a three-week history of weakness, poor appetite, and choking spells during feeding. Other accompanying symptoms include excessive sleeping, constipation and apathy. Her prenatal history is unremarkable. She was delivered vaginally at 38 weeks of gestation. She was born outside the United States. Her weight and length at birth were within normal range. She is exclusively breastfed. Her mother's family history is unremarkable. The identity and family history of her father are unknown. The pertinent physical findings include apathy, weakness, hypotonia, large tongue, sluggish movement, abdominal bloating, and an umbilical hernia. Based on the given information, what is the most likely diagnosis?

Question

A 12-week-old female infant is brought to the office by her mother due to a three-week history of weakness, poor appetite, and choking spells during feeding.  Other accompanying symptoms include excessive sleeping, constipation and apathy.  Her prenatal history is unremarkable.  She was delivered vaginally at 38 weeks of gestation.  She was born outside the United States.  Her weight and length at birth were within normal range.  She is exclusively breastfed.  Her mother's family history is unremarkable.  The identity and family history of her father are unknown.  The pertinent physical findings include apathy, weakness, hypotonia, large tongue, sluggish movement, abdominal bloating, and an umbilical hernia.  Based on the given information, what is the most likely diagnosis?

Quizplus · Accepted Answer

This clinical case is characteristic of congenital hypothyroidism, which may be familial or sporadic. The most common cause is thyroid dysgenesis (i.e., aplasia, hypoplasia, or ectopic gland), which has been incriminated in 85% of cases. Other causes include inborn errors of thyroxin synthesis (10%), and transplacental maternal thyrotropin-receptor blocking antibodies (5%). Infants initially appear normal at birth, but gradually develop apathy, weakness, hypotonia, large tongue, sluggish movement, abdominal bloating, and an umbilical hernia. Other signs include pathologic jaundice, difficult breathing, noisy respiration, hypothermia, and refractory macrocytic anemia. Infants initially appear normal due to the presence of moderate amounts of maternal hormones in the infant's circulation. For this reason, screening is mandated in all states at birth to allow for the early detection, treatment, and consequent improvement of the prognosis. Screening is done by measuring serum T4 and TSH levels. The treatment is levothyroxine (initial dose of 10 mcg/kg, then titrated accordingly). (Choice A) Infant botulism occurs most commonly in infants whose diet includes honey or canned food. This infant has been exclusively breastfed since birth. Furthermore, patients with botulism do not present with a large tongue, umbilical hernia, and apathy, which are all classic features of hypothyroidism. (Choice B) Werdnig-Hoffman syndrome is an autosomal recessive disorder that involves degeneration of the anterior horn cells and cranial nerve motor nuclei. It is a cause of "floppy baby" syndrome (the other cause is infant botulism). (Choice C) Myotonic congenital myopathy is an autosomal dominant disorder characterized by muscle weakness and atrophy (most predominant in the distal muscles of the upper and lower extremities), myotonia, testicular atrophy, and baldness. (Choice E) Myasthenia gravis presents with easy fatigability and weakness that improves with rest. The pediatric form occurs in late childhood or adolescence. Educational objective: Infants with congenital hypothyroidism initially appear normal at birth, but gradually develop apathy, weakness, hypotonia, large tongue, sluggish movement, abdominal bloating, and an umbilical hernia. For this reason, screening newborns for hypothyroidism, along with phenylketonuria and galactosemia, is standardly performed in all states.

A 12-Week-Old Female Infant Is Brought to the Office by Her