A VOMITING INFANT
History
Tom is a 7-week-old infant who presents to the A&E department with a 1-week history of non-bilious vomiting. His mother describes the vomit as ‘shooting out’. He has a good appetite but has lost 300 g since he was last weighed a week earlier. He has mild constipation. The family have recently returned from Spain. There is no vomiting in any other members of the family. His sister suffers from vesicoureteric reflux and urinary tract infections.
Examination
Tom is apyrexial and mildly dehydrated. His pulse is 170 beats/min, blood pressure 82/43 mmHg, and peripheral capillary refill 2 s. There is no organomegaly, masses or tenderness on abdominal examination. There are no signs in the other systems
INVESTIGATIONS
Normal
Haemoglobin 11.7 g/dL 10.5–13.5 g/dL
White cell count 10.0 109/L 4.0–11.0 109/L
Platelets 332 109/L 150–400 109/L
Sodium 134 mmol/L 135–145 mmol/L
Potassium 3.1 mmol/L 3.5–5.0 mmol/L
Chloride 81 mmol/L 98–106 mmol/L
Urea 9.0 mmol/L 1.8–6.4 mmol/L
Creatinine 60 µmol/L 18–35 µmol/L
Capillary gas
pH 7.56 7.36–7.44
PCO2 6.0 kPa 4.0–6.5 kPa
PO2 3.2 kPa 12–15 kPa
HCO3 38 mmol/L 22–29 mmol/L
Base excess 10 ( 2.5)–(2.5) mmol/L
Urine dipstick No abnormality detected
Questions
• What is the likely diagnosis?
• What is the differential diagnosis?
• How would you confirm the diagnosis?
• What is the treatment?
Medicine
In an infant this age with non-bilious projectile vomiting, pyloric stenosis is the most likely diagnosis. This condition presents between 2 weeks and 5 months of age (median 6 weeks) and projectile vomiting is typical. The vomitus is never bile-stained as the obstruction is proximal to the duodenum. As in this case, infants may also be constipated. The hypochloraemic alkalosis is characteristic and is due to vomiting HCl. The low potassium is due to the kidneys retaining hydrogen ions in favour of potassium ions. The raised urea and creatinine suggest that there is also mild dehydration. The male-to-female ratio is 4:1 and occasionally there is a family history (multifactorial inheritance).
Differential diagnosis
• Gastro-oesophageal reflux
• Gastritis
• Urinary tract infection
• Overfeeding
Gastro-oesophageal reflux usually presents from or shortly after birth. Gastritis usually occurs with an enteritis and diarrhoea. A urinary infection at this age may present in a very non-specific way and therefore it is mandatory to test the urine. The absence of nitrites and leucocytes in the urine dipstick makes a urinary infection very unlikely. Overfeeding should be elucidated from a careful history. The diagnosis could be clinically confirmed by carrying out a test feed. A feed leads to peristalsis which occurs from left to right. The abdominal wall is usually relaxed during a feed, making palpation easier. A pyloric mass, which is the size of a 2-cm olive, may be felt in the right hypochodrium by careful palpation. An ultrasound is also usually done for further confirmation. Tom is slightly tachycardic (pulse rate 1 year, 110–160 beats/min) with a normal blood pressure and capillary refill time. His urea is slightly elevated. Initial treatment consists of treating the dehydration, acid–base and electrolyte abnormalities with intravenous fluids (0.9 per cent saline with 5 per cent dextrose and added KCl would be the appropriate starting fluid in this infant with a low sodium and potassium). Feeds should be stopped, a nasogastric tube inserted and the stomach emptied. The definitive operation is Ramstedt’s pyloromyotomy.
KEY POINTS
• The peak age of presentation of pyloric stenosis is 6 weeks.
• The typical biochemical picture is a hypochloraemic alkalosis.
• The definitive treatment is Ramstedt’s pyloromyotomy
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