A 5-week-old boy is brought to the office by his mother due to vomiting. The mother explains, "Over the past 4 days, my son has been vomiting forcefully right after drinking his formula. He used to spit up after feeding, but it has been getting worse, and now, he seems to throw up everything he eats." The emesis is the color of milk. The patient has had fewer wet diapers today and a single stool yesterday. He was born at 39 weeks gestation after an uncomplicated pregnancy. Newborn metabolic screening was normal. Medical history is notable for switching to formula at age 2 weeks due to low breast milk production. At that time, the patient was at the 25th percentile for length, weight, and head circumference. Today, he is at the 10th percentile for weight, although length and head circumference remain at the 25th percentile. Temperature is 36.7 C (98.1 F) and pulse is 169/min. Physical examination shows an awake, alert, slightly fussy infant. The anterior fontanelle is open and mildly sunken. The lips and mucous membranes are slightly dry. Cardiopulmonary examination shows no abnormalities. The abdomen is soft and nondistended with active bowel sounds, although waves of peristalsis are visible. There is no hepatosplenomegaly or tenderness to palpation. Serum chemistry is pending.
Which of the following is the most appropriate next step in management of this patient?

Question

A 5-week-old boy is brought to the office by his mother due to vomiting.  The mother explains, "Over the past 4 days, my son has been vomiting forcefully right after drinking his formula.  He used to spit up after feeding, but it has been getting worse, and now, he seems to throw up everything he eats."  The emesis is the color of milk.  The patient has had fewer wet diapers today and a single stool yesterday.  He was born at 39 weeks gestation after an uncomplicated pregnancy.  Newborn metabolic screening was normal.  Medical history is notable for switching to formula at age 2 weeks due to low breast milk production.  At that time, the patient was at the 25th percentile for length, weight, and head circumference.  Today, he is at the 10th percentile for weight, although length and head circumference remain at the 25th percentile.  Temperature is 36.7 C (98.1 F) and pulse is 169/min.  Physical examination shows an awake, alert, slightly fussy infant.  The anterior fontanelle is open and mildly sunken.  The lips and mucous membranes are slightly dry.  Cardiopulmonary examination shows no abnormalities.  The abdomen is soft and nondistended with active bowel sounds, although waves of peristalsis are visible.  There is no hepatosplenomegaly or tenderness to palpation.  Serum chemistry is pending. 
Which of the following is the most appropriate next step in management of this patient?

Quizplus · Accepted Answer

Explanation: 11ec2b69_bf3f_2682_8f63_411476048929_MD0005_00 This young patient has findings concerning for infantile hypertrophic pyloric stenosis, a condition characterized by smooth muscle hypertrophy of the pylorus. Pyloric hypertrophy results in gastric outlet obstruction and impedes the passage of milk, resulting in the classic symptom of nonbilious, projectile emesis most commonly seen in firstborn boys age 3-6 weeks. Vomiting usually occurs immediately after oral intake, as seen in this patient, and infants classically have signs of hunger soon after. Palpation often demonstrates the hypertrophied muscle as an olive-shaped abdominal mass in the epigastrium, although its absence does not exclude the diagnosis. Visually prominent peristaltic waves may be seen and represent exaggerated gastric contractions attempting to move food beyond the obstruction. Dehydration is common, as seen in this patient with decreased urine output, a sunken fontanelle, dry mucous membranes, and a drop in weight percentiles. The diagnosis is confirmed by abdominal ultrasound, which reveals a thickened, elongated pylorus muscle. thickened, elongated pylorus muscle (Choices A and D) Gastroesophageal reflux disease is a common cause of nonbilious emesis in infants, and treatment may include proton pump inhibitor therapy and/or avoidance of milk and soy proteins (eg, hydrolyzed formula). However, symptoms are typically chronic, not acute, and most commonly consist of effortless regurgitation, not forceful vomiting. (Choice C) Increased intracranial pressure can cause projectile, nonbilious emesis and can be evaluated via ultrasonography of the head through an infant's open fontanelle. However, additional findings typically include a rapidly increasing head circumference (not seen in this patient) and a bulging, not sunken, fontanelle. Moreover, visibly prominent peristalsis suggests a gastrointestinal cause of vomiting. (Choice E) Nonbilious vomiting and poor weight gain can be presenting signs of some inborn errors of metabolism (eg, galactosemia). However, repeating negative newborn screening tests is generally of low diagnostic yield because they are highly sensitive. Because of the acute history of forceful vomiting, abdominal imaging should be prioritized; disease-specific testing for an inborn error may be considered if imaging is negative and the vomiting persists. Educational objective: Infantile hypertrophic pyloric stenosis typically presents in infants age 3-6 weeks with projectile vomiting immediately after feeding and with dehydration; visible peristalsis or a palpable, epigastric ovoid mass is common. Abdominal ultrasound is diagnostic. References: Contemporary management of pyloric stenosis. (http://www.ncbi.nlm.nih.gov/pubmed/27521712)

A 5-Week-Old Boy Is Brought to the Office by His