History
Typical presentation of an infant with hypertrophic pyloric stenosis (HPS) is onset of initially nonbloody, always nonbilious vomiting at 4-8 weeks. Although vomiting may initially be infrequent, over several days it becomes more predictable, occurring at nearly every feeding. Vomiting intensity also increases until pathognomonic projectile vomiting ensues. Slight hematemesis of either bright red flecks or a coffee-ground appearance is sometimes observed.
Patients are usually not ill-looking or febrile. The baby in the early stage of the disease remains hungry and sucks vigorously after episodes of vomiting.
Prolonged delay in diagnosis can lead to dehydration, poor weight gain, malnutrition, metabolic alterations, and lethargy.
Parents often report trying several different baby formulas because they (or their physicians) assume vomiting is due to intolerance.
Physical
Careful physical examination provides a definitive diagnosis for most infants with hypertrophic pyloric stenosis. However, some of the classic signs that would lead to diagnosis may be absent due, in part, to the early diagnosis of hypertrophic pyloric stenosis.
An enlarged pylorus, classically described as an "olive," can be palpated in the right upper quadrant or epigastrium of the abdomen in 60-80% of infants. [2] In order to assess the pylorus, the patient must be calm and cooperative. A pacifier or small amount of dextrose water may help. If the stomach is distended, aspiration using a nasogastric tube is necessary. With the infant supine and the examiner on the child's left side, gently palpate the liver edge near the xiphoid process. Then displace the liver superiorly; downward palpation should reveal the pyloric olive just on or to the right of the midline. To be assured of the diagnosis, the physician should be able to roll the pylorus beneath the examining finger. The tumor (mass) is best felt after vomiting or during, or at the end of, feeding. The diagnosis is easily made if the presenting clinical features are typical, with projectile vomiting, visible peristalsis, and a palpable pyloric tumor.
When diagnosis is delayed, the infant may develop severe constipation associated with signs of dehydration, malnutrition, lethargy, and shock.
Causes
Despite numerous hypotheses, the exact etiology of hypertrophic pyloric stenosis is not fully understood. Genetic, extrinsic and hormonal factors have been implicated. In addition, abnormalities of various components of the pyloric muscle, such as smooth muscle cells, growth factors, extracellular matrix elements, nerve and ganglion cells, neurotransmitters, and interstitial cells of Cajal, have been reported. Genetic studies have identified susceptibility loci, and molecular studies have concluded that smooth muscle cells are not properly innervated in this condition. [18] Kundal et al reported a rare case of dizygotic twins who were bottle fed and were affected with infantile hypertrophic pyloric stenosis. [19]
Bottle-feeding was associated with an increased risk for hypertrophic pyloric stenosis in a population-based case-control study of 714 infants. [20, 21] After adjustment for sex, race, maternal smoking status, and other factors, bottle-feeding was associated with an increased risk for hypertrophic pyloric stenosis (odds ratio [OR], 2.31; 95% confidence interval, 1.81-2.95) compared with breast feeding. This effect was most pronounced in the children of older and multiparous mothers. [20, 21]
Infant and maternal use of macrolides also appears to increase the risk of infantile hypertrophic pyloric stenosis. In an analysis of 999,378 live-born Danish singletons from a nationwide, register-based cohort (1996-2011), Lund et al found that infantile HPS appeared to be associated with the use of macrolide antibiotics in young infants, pregnant women in late pregnancy, and early postpartum (≤2 wk) women. [22, 23] Because macrolide antibiotic treatment of young infants was strongly associated with infantile hypertrophic pyloric stenosis, the investigators cautioned to only administer these agents if the potential treatment benefits outweigh the risk. [22, 23]
