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  • Pyloric stenosis presents most commonly between 5 to 6 weeks of age.

  • Progressive non-bilious projectile vomiting is the most common presenting symptom.

  • The typical electrolyte imbalance is hypochloremic metabolic alkalosis.

  • Diagnosis is confirmed by ultrasound, and rarely by a fluoroscopic upper GI contrast study.

  • Treatment is surgical pyloromyotomy.

Pyloric stenosis, also known as infantile hypertrophic pyloric stenosis (IHPS), is a condition affecting young infants in which the pylorus muscle becomes abnormally thickened, causing obstruction to gastric emptying. It is most often seen in the first few weeks of life, with the most common age of presentation between 5 and 6 weeks with a range of 2 to 31 weeks.1,2 Although premature infants may present later than term babies (6 weeks compared with 5 weeks, respectively), their presentation is actually earlier when measured from postmenstrual age (40 weeks vs. 45 weeks, respectively).2 Its incidence has been reported to be 3 per 1000 live births in the Western world. Lower incidence ranges have been reported for Asian children, with reports between 0.3 to 0.5 per 1000 infants in Taiwanese infants.3,4 A recent decline in IHPS has been reported both in the United States and several European countries concurrent with a declining incidence of sudden infant death syndrome, leading to some belief that recommended supine sleeping position may be responsible for both declines.5 A genetic predisposition has been noted with an increased incidence of siblings and a strong increased incidence in twins, both monozygotic and dizygotic.6,7 It is unclear if the increased incidence in twins is due to genetic or environmental causes but genetic tests have identified a number of potential loci, specifically chromosomes 3 and 5, and further studies are ongoing.8–10 There is nearly a four- to fivefold male predominance, and an increased incidence in premature infants.2 The highest incidence reported is in first-born infants, although this may be due to more families having only one child than two or three children.9,11 Environmental and mechanical factors have been implicated as potential causes. Infants that were breastfed exclusively have a much lower risk of developing IHPS compared with infants that have been bottle-fed or bottle-fed and breastfed.12,13 Very early exposure to erythromycin has been associated with a nearly eight- to tenfold increased risk of developing IHPS.14,15 Erythromycin is a motilin agonist, and thus it produces strong gastric and pyloric contractions. Infants exposed to erythromycin through breast milk may also be at risk for developing IHPS, but the data are not as conclusive.16 Case reports and a more recent study have also demonstrated that exposure to oral azithromycin is associated with up to an eightfold increased risk of IHPS in the first 6 weeks of life, with the greatest risk if exposure occurs within the first 2 weeks of life.17,18 However, the complications for pertussis ...

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