A 41-year-old man comes to the emergency department due to 4 days of rapidly worsening dyspnea, nonproductive cough, fever, and chills. The patient developed acute liver failure due to Wilson disease and underwent orthotopic liver transplantation 5 months ago. He takes several immunosuppressants, including a glucocorticoid, but no antibiotics. The patient does not use tobacco, alcohol, or illicit drugs. Temperature is 38.9 C (102 F), blood pressure is 116/72 mm Hg, pulse is 112/min, and respirations are 28/min. Oxygen saturation is 82% on ambient air. Pulmonary examination reveals bilateral crackles. Leukocyte count is 12,000/mm³ and serum lactate dehydrogenase level is 330 U/L. Chest x-ray reveals bilateral, diffuse interstitial infiltrates. An adequate sputum sample cannot be obtained. Which of the following tests is most likely to yield the diagnosis in this patient?

Question

Quizplus · Accepted Answer

Patients receiving immunosuppressive therapy following solid organ transplantation are at high risk for opportunistic infections, most notably Pneumocystis pneumonia (PCP) and cytomegalovirus (CMV). Risk is usually greatest during the 6 months following transplantation, when immunosuppressive regimens tend to be most intensive. Therefore, primary prophylaxis with trimethoprim-sulfamethoxazole (for PCP) and ganciclovir-valganciclovir (for CMV in seropositive patients) is typically administered during this period. Patients who develop PCP while on immunosuppressive therapy usually present with acute respiratory failure (tachypnea, hypoxia), dry cough, and fever. Lactate dehydrogenase (LDH) levels are usually elevated, and chest x-ray classically reveals bilateral, diffuse interstitial infiltrates. The diagnosis work-up generally begins with microscopy of induced sputum to identify the causative organism, Pneumocystis jirovecii. When this test is nondiagnostic or cannot be obtained, patients require bronchoscopy with bronchoalveolar lavage. bilateral, diffuse interstitial infiltrates (Choice A) The cell wall of P jirovecii contains beta-D-glucan; therefore, serum testing for this protein is generally positive in those with PCP. However, because many fungal infections (eg, Aspergillus, Candida) increase serum levels of beta-D-glucan (a component of the cell wall in most fungi), this test cannot be used to definitively diagnose PCP. Diagnostic confirmation requires the identification of P jirovecii in a respiratory sample. (Choice B) Although blood cultures are typically obtained in febrile patients and can often identify circulating bacterial or fungal organisms, they are unlikely to yield the diagnosis in this patient because P jirovecii cannot be cultured; it must be identified in respiratory samples using specialized microscopy stains. (Choice D) High-resolution CT scan can define lung pathology and is likely to reveal ground-glass pulmonary opacities in this patient. However, diagnostic confirmation requires the identification of the causative agent in a respiratory sample, not additional imaging. (Choice E) Nasopharyngeal swab can diagnose several upper respiratory viruses and some bacterial pathogens (eg, Streptococcus pyogenes). Although viral pneumonia could cause interstitial infiltrates, fever, and respiratory failure, PCP is more likely in this immunosuppressed patient who has elevated LDH levels and is not on PCP prophylaxis. (Choice F) Legionella typically causes gastrointestinal symptoms and high fever (usually >39 C [102.2 F]) prior to the onset of a lobar pneumonia. The lack of gastrointestinal symptoms, and the presence of interstitial infiltrates and elevated LDH, make PCP far more likely. Educational objective: Pneumocystis pneumonia is a common opportunistic infection in patients taking immunosuppressant medication after solid organ transplantation. Diagnosis requires the identification of Pneumocystis jirovecii organisms in respiratory secretions using microscopy with specialized stains. Samples are obtained using induced sputum or, if this is unrevealing, bronchoscopy with bronchoalveolar lavage.

A 41-Year-Old Man Comes to the Emergency Department Due to 4