Case 20 – A 1-month-old girl with failure to thrive

A 1-month-old white girl is sent to the emergency room by her pediatrician for failure to thrive. She was born at full term, weighing 2.72 kg (6 lb), via spontaneous vaginal delivery with no complications. She was discharged to home with her mother and has been feeding well; she takes 3-4 ounces of formula every 2-3 hours. Her parents deny any emesis, fevers, or diarrhea, although her mother notes frequent foul-smelling loose stools. Family history is unremarkable. She lives with her parents and four siblings. She is afebrile with normal vital signs. Her weight is 3.3 kg (7.3 lb) (<5th percentile), length is 50 cm (19.7 in) (<5th percentile), and head circumference is 37 cm (14.6 in) (at 10th percentile). She is cachetic but interactive. The remainder of her examination is unremarkable.

What is the definition of failure to thrive (FTT)?

The term FTT may be attributed to a child who meets any of the following criteria:

1. Has weight <5th percentile for age and sex
2. Has depressed weight for height
3. Has a rate of weight gain that causes a decrease across two or more major percentile lines over time
4. Has a rate of daily weight gain less than expected for age

What are the two types of FTT?

Organic causes of FTT include:

1. Abnormal loss of calories
2. An abnormal need for calories
3. Failure to ingest an appropriate number of calories
4. Failure to metabolize

Most cases of FTT are due to nonorganic causes, typically psychosocial factors.

What organic causes of FTT should be considered in patients <6 months old?

1. Cystic fibrosis
2. Gastroesophageal reflux
3. HIV infection
4. Inborn errors of metabolism
5. Milk-protein intolerance
6. Perinatal or postnatal infections
7. Renal tubular acidosis

While in the hospital the patient feeds well, but despite adequate caloric intake, she fails to gain weight. What tests should be included in the initial work-up of this patient’s cause of FTT?

Malabsorption must be considered when a patient fails to gain weight despite feeding well. Initial screening studies for malabsorption include:

1. Serum electrolytes, albumin, and total protein
2. Stool exam for Clostridium difficile, ova, and parasites and stool cultures for bacterial pathogens
3. Stool exam for occult blood, leukocytes, reducing substances, and pH
4. Urinalysis and culture

What is the most likely diagnosis in this patient, and how should it be confirmed?

Since this patient is a white person with a history of FTT, malabsorption, and foul-smelling stools, cystic fibrosis must be considered. The next step in the work-up of this patient should be a sweat chloride test, which is the gold standard for the diagnosis of cystic fibrosis.

How should this patient’s malabsorption be treated?

The mainstay of treatment for pancreatic insufficiency in cystic fibrosis is pancreatic enzyme replacement. In addition, patients should receive supplementation of fat-soluble vitamins (vitamins A, D, E, and K).

By Jessica Kagen Hart, Resident, Department of General Pediatrics, Children’s Hospital of Philadelphia; in association with Le TT, Schabelman E, Shivaram A, and Klein J, eds: First Aid Cases for the USMLE Step 2 CK. New York: McGraw-Hill, 2007.