Approach to growth faltering Quiz: Ace Your Exams

A 15-month-old boy is evaluated in the clinic for poor weight gain. Solid food was introduced at six months. His parents offer three meals a day but report he is a very picky eater. He eats fruits and breastfeeds although the patient’s mother is unsure of her supply. Parents report that the infant nurses on demand and drinks two cups of juice daily. The infant has adequate wet diapers each day, and two bowel movements daily. Stools are loose but without blood or mucus. There is no history of difficulty feeding, choking, or vomiting. Family history is non-contributory. The Infant was born at full term without complications at birth or during the pregnancy. Newborn screening tests were normal. Development has been appropriate for age. Temperature is 37° C (98.6° F), pulse is 100/min, respirations are 25/min, blood pressure is 90/52 mm Hg, and oxygen saturation is 98% on room air. Weight has dropped from the 45^th percentile to the 10^th percentile over the last four months. Height and head circumference are at the 25^th percentile. On physical examination, the patient is well-appearing and in no acute distress. No dysmorphic facial features are noted.  Pulmonary and abdominal exams are normal. A soft 1/6 flow murmur is appreciated at the left sternal border. An erythematous diaper rash is present. Complete blood count is shown below. Thyroid profile, liver and kidney functions are normal. Which of the following is the most probable cause of this patient’s symptoms?  
 

Laboratory value	Result
Leukocyte count	8,500/mm³
Hemoglobin	9.2 g/dL
Mean corpuscular volume (MCV)	68 fl
Platelet count	320,000/mm³