A 10-year-old boy is brought to the clinic by his adoptive parents due to a worsening cough. The patient has had a productive cough with yellow-green sputum since his parents adopted him at age 7 from a developing country. A tuberculin skin test at the time of immigration revealed a 3-mm induration. The patient's cough has worsened over the past 3 days, and this morning he had a fever of 38.3 C (101 F). His parents kept him home from school, and he has been resting in bed. The patient has been hospitalized twice in the past year for pneumonia. Temperature is 38.1 C (100.6 F). Height and weight, which were at the 25th percentile 2 years ago, are now at the 5th percentile. The patient is a thin, cooperative child in no acute distress. Auscultation of the lungs reveals scattered bilateral rhonchi and wheezes. Cardiac examination reveals a regular rhythm and no murmurs. The abdomen is soft and nontender with hard stool palpable in the right lower quadrant. Chest x-ray reveals hyperinflation with increased bronchovascular markings throughout and several parallel linear opacities in the bilateral upper lobe parenchyma. Which of the following would most likely establish the diagnosis in this patient?

Question

A 10-year-old boy is brought to the clinic by his adoptive parents due to a worsening cough.  The patient has had a productive cough with yellow-green sputum since his parents adopted him at age 7 from a developing country.  A tuberculin skin test at the time of immigration revealed a 3-mm induration.  The patient's cough has worsened over the past 3 days, and this morning he had a fever of 38.3 C (101 F).  His parents kept him home from school, and he has been resting in bed.  The patient has been hospitalized twice in the past year for pneumonia.  Temperature is 38.1 C (100.6 F).  Height and weight, which were at the 25th percentile 2 years ago, are now at the 5th percentile.  The patient is a thin, cooperative child in no acute distress.  Auscultation of the lungs reveals scattered bilateral rhonchi and wheezes.  Cardiac examination reveals a regular rhythm and no murmurs.  The abdomen is soft and nontender with hard stool palpable in the right lower quadrant.  Chest x-ray reveals hyperinflation with increased bronchovascular markings throughout and several parallel linear opacities in the bilateral upper lobe parenchyma.  Which of the following would most likely establish the diagnosis in this patient?

Quizplus · Accepted Answer

Explanation: 11ec2b69_c07d_4be0_8f63_4183f69224fc_MD0005_00 This patient has a chronic, productive cough, recurrent respiratory infections, and weight loss, suspicious for cystic fibrosis (CF). An autosomal recessive mutation affecting the CF transmembrane conductance regulator gene impairs chloride transport, resulting in abnormally thick secretions. In the lungs, viscous secretions allow bacteria (eg, Staphylococcus aureus, Pseudomonas aeruginosa) to colonize, predisposing the patient to frequent infection. Mucus plugs the airways and leads to hyperinflation from chronic obstruction and bronchiectasis, as seen on this patient's x-ray. Thick intestinal secretions leave the gastrointestinal tract dehydrated and prone to constipation (as seen in this patient with stool palpable in the right lower quadrant) and obstruction. In addition, mucus blocks the pancreatic ducts and impairs enzyme secretion, resulting in malabsorption, failure to thrive, and often CF-related diabetes. x-ray CF is being increasingly recognized in different parts of the world. Newborn screening frequently identifies patients with CF in the United States; however, this patient was born in a developing country and was likely not screened. The sweat chloride test is the gold standard for detecting CF, and 2 elevated sweat chloride levels in a symptomatic patient are diagnostic. (Choices A and D) Adenosine deaminase activity is reduced in a common form of severe combined immunodeficiency (SCID). SCID and HIV cause failure to thrive and severe bacterial, fungal (eg, Pneumocystis jirovecii, Candida), and viral (eg, herpes simplex virus, cytomegalovirus, Epstein-Barr virus) diseases. However, SCID typically presents within the first few months of life, and both SCID and HIV tend to be associated with infectious diarrhea rather than constipation. (Choice B) Dihydrorhodamine 123 oxidation test is diagnostic for chronic granulomatous disease, an X-linked immune disorder characterized by severe bacterial and fungal pneumonias and skin infections. Chronic granulomatous disease is unlikely in this child with no history of abscesses. (Choice C) Quantitative immunoglobulins are low in patients with common variable immunodeficiency. Recurrent infections and bronchiectasis are common; however, diarrhea, rather than constipation, would be expected. Educational objective: Cystic fibrosis should be suspected in children with recurrent respiratory infections, bronchiectasis, constipation, and failure to thrive. The sweat chloride test is the gold standard for diagnosis. References: The diagnosis of cystic fibrosis. (http://www.ncbi.nlm.nih.gov/pubmed/28576637)

A 10-Year-Old Boy Is Brought to the Clinic by His