A 1-year-old boy is brought to the clinic due to poor weight gain. The patient's mother is concerned that he is smaller than children of the same age. He drinks 600 mL (20 oz) of whole milk daily and eats table food such as meats, fruits, and grains 3 times a day. Since the introduction of solid foods, the child has had an increase in bulky bowel movements, occurring 5-6 times daily. The patient also has frequent coughing episodes. He has not had any previous surgeries. The family lives in a rural area. Temperature is 37.1 C (98.8 F), pulse is 120/min, and respirations are 24/min. Physical examination shows a thin but active child. The oropharynx is clear, and there is no cervical lymphadenopathy. Pulmonary examination reveals a wet cough with bilateral rhonchi. The abdomen is soft with no organomegaly. Growth chart shows:
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Which of the following is the most likely cause of this patient's symptoms?
Cystic fibrosis | |
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CFTR = cystic fibrosis transmembrane conductance regulator. | |
This patient has features of cystic fibrosis (CF), an autosomal recessive disorder caused by a defective CF transmembrane conductance regulator (CFTR). Impaired chloride transport via CFTR results in viscous secretions in the lungs, sinuses, and pancreas. Newborn screening identifies only the most common CFTR mutations; therefore, CF should be considered in a patient with failure to thrive and recurrent respiratory symptoms (eg, frequent coughing episodes, cough with bilateral rhonchi), regardless of screening results.
The most common gastrointestinal manifestation of CF is pancreatic insufficiency. Pancreatic duct obstruction from viscous mucus prevents digestive enzymes from reaching the intestines and leads to progressive pancreatic inflammation and fibrosis. Fat and protein malabsorption occur, leading to steatorrhea (bulky, greasy stools), growth failure, and fat-soluble vitamin deficiencies (ie, A, D, E, and K).
A typical CF growth chart shows normal birth measurements with subsequent failure to thrive, characterized by weight deceleration crossing ≥2 major percentiles (eg, 25th, 10th) followed by a deceleration in linear growth velocity. In addition to malabsorption, recurrent sinopulmonary infections impair growth due to poor appetite and increased metabolic needs during illness.
(Choice A) Celiac disease, an autoimmunity to gluten, can result in failure to thrive but typically causes chronic diarrhea and often abdominal pain and/or distension. In addition, although celiac disease increases the risk of IgA deficiency, which can cause respiratory symptoms in a minority of patients, the association is rare.
(Choice B) Chronic Giardia infection can cause weight loss and malabsorption; however, stools are typically loose, and respiratory symptoms are not expected.
(Choice C) Constitutional growth delay typically presents with short stature in older children who have a deceleration in linear growth velocity in infancy that normalizes after age 2-3. These children do not have associated respiratory or gastrointestinal symptoms.
(Choice D) Food protein–induced allergic proctocolitis (ie, milk protein intolerance) typically presents in the first few months of life with blood-streaked stools. This patient's age and the presence of respiratory symptoms make this diagnosis unlikely.
(Choice E) Lactose intolerance is characterized by abdominal cramping, bloating, and diarrhea after ingestion of lactose-containing products. It is uncommon in children age <6 and is not associated with respiratory problems.
Educational objective:
Failure to thrive and recurrent respiratory symptoms should raise concern for cystic fibrosis (CF). Pancreatic insufficiency occurs in CF and causes fat and protein malabsorption, resulting in steatorrhea, vitamin deficiencies, and poor weight gain.