Differential Diagnosis for a Week-Old Boy with Vomiting and Poor Feeding
The patient's presentation of vomiting, poor feeding, sunken eyes, depressed anterior fontanelle, dry mucous membranes, and laboratory results suggest a condition affecting fluid and electrolyte balance. The key findings include hyponatremia (low sodium), hyperkalemia (high potassium), and signs of dehydration.
Single Most Likely Diagnosis
- Congenital Adrenal Hyperplasia (CAH) due to 21-hydroxylase deficiency: This condition leads to an inability to produce aldosterone and cortisol, resulting in hyponatremia, hyperkalemia, and dehydration. The elevated 17-hydroxyprogesterone level is a hallmark of this disorder, making B. 17-hydroxyprogesterone the most likely increased substance in this patient.
Other Likely Diagnoses
- Adrenal insufficiency: This could explain the electrolyte imbalance and dehydration but would typically present with hypotension and might not fully account for the specific pattern of electrolyte abnormalities seen here.
- Renal tubular acidosis or other renal disorders: These could lead to electrolyte imbalances but might not fully explain the clinical presentation and the specific laboratory findings.
Do Not Miss Diagnoses
- Intestinal obstruction: Although no abdominal masses are noted, conditions like pyloric stenosis or intestinal obstruction could cause vomiting and dehydration. Missing this diagnosis could lead to severe consequences, including perforation and peritonitis.
- Infections (e.g., urinary tract infection, sepsis): These can cause dehydration, electrolyte imbalances, and could be life-threatening if not promptly treated.
- Congenital heart disease: While not directly suggested by the electrolyte imbalance, heart disease could lead to poor feeding and dehydration due to increased energy expenditure and might be associated with other signs not yet apparent.
Rare Diagnoses
- Other forms of CAH (e.g., 11-beta hydroxylase deficiency): These could also lead to electrolyte imbalances but are less common than 21-hydroxylase deficiency.
- Bartter syndrome or Gitelman syndrome: These are rare genetic disorders affecting the kidneys' ability to reabsorb electrolytes, leading to hypokalemic alkalosis, which does not match this patient's hyperkalemia.
- Pseudohypoaldosteronism: A rare condition where the body does not respond to aldosterone, leading to hyperkalemia and hyponatremia, but this would typically present with more pronounced hypotension and might not fully explain the clinical scenario.