The newborn appeared to be gaining weight at his two-week well-child visit, but at 9-weeks had lost 2700 grams, and was now below his birth weight. Also, the infant's mother reported that he was often spitting up after feeds. The mother had switched from breastfeeding in the hospital nursery to one formula and then another at home, which may have played a role, the family's pediatrician said. Suspecting a reflux disorder, he recommended the mother add cereal to thicken the formula. But still the weight loss persisted, prompting the pediatrician to refer the patient to Hopkins Children’s ED for an evaluation.

In the ED the mother reported that the child had not experienced fever or lethargy, runny nose, cough, or difficulty breathing. There were no reports of cyanosis, diaphoresis or profuse sweating, foul-smelling urine, rashes or skin lesions. His history included no acute illnesses or trauma, hospitalizations or surgeries, and no early or unexplained death in the family. On exam his heart rate was normal. He was, pediatric resident Susan Davidson said, “behaving in a normal way for a baby of his age.”

But the most impressive finding, she added, was the folds of skin hanging off his lower extremities: “He reminded me of a child from a third-world country suffering famine.”

The child’s appearance and severe failure to thrive pushed Davidson and the team to look for possible metabolic abnormalities. The results of laboratory studies were striking: the baby had profound hypochloremia, with a chloride level nearly half that of normal, and severe alkalosis, with a bicarbonate level more than double the normal level. He also had severe hyponatremia, or low sodium levels, and hypokalemia, or low postassium.

“This baby had a profound hypochloremic metabolic alkalosis,” said pediatric nephrology fellow Erum Hartung. “The severity of the electrolyte abnormalities made us wonder if there was anything else going on.”

But what? In working up differential diagnoses of metabolic alkalosis, Hartung said, think first of gastrointestinal hydrogen loss due to vomiting. Although this baby was spitting up with every feed, according to his mother, he improved slightly with the change in formula. Another potential cause could be excessive loss of chloride in sweat, a sign of cystic fibrosis (CF). But this baby's newborn screening test for CF was normal. Intake of excessive amount of alkali, such as baking soda, can also cause metabolic alkalosis if the kidneys are unable to excrete the excess bicarbonate. Metabolic alkalosis can also occur if there is hydrogen loss from the kidneys, either due to medications such as loop or thiazides diuretics, or due to genetic metabolic disorders such as Bartter’s or Gitelman’s syndrome. These two rare autosomal recessive disorders are caused by defects in ion channels in the kidney, and cause hypochloremic metabolic alkalosis. However, they also tend to show high urine chloride, which did not appear in this baby.

Searching for a possible kidney problem, the team ordered a renal ultrasound. Serendipitously, this uncovered the true cause of the child’s weight loss and vomiting. The kidneys and bladder were normal, but something else on the screen was not – the pylorus, a canal that connects the stomach to the duodenum. In this child the ring-size muscle in the pylorus had enlarged to the point where food could not empty out of the stomach.

“Thus, the diagnosis, pyloric stenosis, was made,” said Davidson.

Also known as gastric outlet obstruction, hypertrophic pyloric stenosis is fairly common, affecting about three out of 1000 births in the United States. The condition is about four times more likely to occur in firstborn male infants, has been shown to run in families, and occurs more commonly in Caucasian infants. Most affected infants are usually between 2-weeks and 2-months-of-age, with symptoms usually appearing during or after the third week of life. The hallmark sign of the disorder is projectile vomiting, which the mother described as spitting up.

"I think this is a lesson in how history is everything," said Hartung. "If we had known the extent of vomiting, the diagnosis wouldn't have been such a mystery."

Another hallmark sign is a hard, olive-size tumor in the pylorus, palpable in the right upper quadrant on exam.

First fully described more than a century ago by Danish pediatrician Harald Hirschsprung, pyloric stenosis was medically managed with little success until 1911, when Conrad Ramstedt described success with pyloromyotomy, in which surgeons make an incision along the pylorus muscle to relax the canal and allow food to pass. Today, this operation is still the standard of care, though pediatric surgeons often use a minimally invasive endoscopic approach to reduce scarring.

“Most surgeons have adopted the minimally-invasive procedure for better cosmesis,” said pediatric surgery fellow Stefan Scholz. “There is an extremely low mortality. No one should die of this today.”

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