A 4-year-old boy is brought to the emergency department for difficulty breathing and a productive cough. He has a past medical history of recurrent episodes of sinusitis and otitis media. The respiratory infections typically have a protracted course but respond to high-dose antibiotic therapy. Pulmonary auscultation shows crackles and wheezing. Cardiovascular examination shows a cardiac point of maximal impulse that is palpated at the right 5th intercostal space. Which of the following is most likely to be dysfunctional in this patient?

Question

A 4-year-old boy is brought to the emergency department for difficulty breathing and a productive cough.  He has a past medical history of recurrent episodes of sinusitis and otitis media.  The respiratory infections typically have a protracted course but respond to high-dose antibiotic therapy.  Pulmonary auscultation shows crackles and wheezing.  Cardiovascular examination shows a cardiac point of maximal impulse that is palpated at the right 5th intercostal space.  Which of the following is most likely to be dysfunctional in this patient?

Quizplus · Accepted Answer

11ec160b_37db_41da_9249_79906d10c037_MD0001_00 This patient's history of recurrent respiratory infections and dextrocardia on physical examination are suggestive of Kartagener syndrome, a form of primary ciliary dyskinesia (PCD). This autosomal recessive condition is caused by a wide variety of mutations that impair ciliary structure or function. Eukaryotic flagella and cilia are composed of a central core known as the axoneme that is surrounded by cell membrane. The axoneme of flagella and motile cilia consists of a circular array of microtubule doublets surrounding 2 central microtubules (9+2 arrangement); the axoneme is anchored to the cell by a basal body. Each doublet has an A and B subunit and is connected to the adjacent doublet via dynein arms. These dynein arms contain an ATPase that generates energy to slide the microtubules past each other, producing ciliary movement. Primary ciliary dyskinesia can result from failure of the dynein arms to develop normally. Patients with PCD experience recurrent respiratory infections (eg, chronic sinusitis, bronchiectasis) as a result of impaired mucociliary clearance. In addition, impaired ciliary movement during embryogenesis can cause situs inversus (reversed right/left positioning of internal organs). Infertility in men (impaired sperm motility) and women (immobility of fallopian tube cilia) is another frequent manifestation. (Choice A) Deficiency of the C1 complement component causes increased susceptibility to encapsulated bacteria (eg, Streptococcus pneumoniae, Haemophilus influenzae, Neisseria meningitidis) and also predisposes to developing systemic lupus erythematosus. (Choice B) Epithelial cell chloride channels are defective in cystic fibrosis. Although patients with cystic fibrosis typically have recurrent respiratory infections and infertility, dextrocardia/situs inversus are not seen. (Choice D) Defects in T-cell IL-2 receptors can cause severe combined immunodeficiency disease (SCID). (Choice E) Immunoglobulin gene rearrangement is impaired in hyper-IgM syndrome. In this disorder, B cells produce high amounts of IgM but are unable to switch production to other immunoglobulin classes. (Choice F) NADPH oxidase deficiency causes chronic granulomatous disease. Educational objective: Kartagener syndrome is a form of primary ciliary dyskinesia characterized by the triad of situs inversus, chronic sinusitis, and bronchiectasis. It occurs due to mutations that impair the structure or function of cilia. Cystic fibrosis also causes chronic respiratory infections, but it is not associated with situs inversus.

A 4-Year-Old Boy Is Brought to the Emergency Department for Difficulty