A 35-year-old man who received a kidney transplant one year ago comes to the emergency department with pleuritic chest pain and cough. He is found to have a low-grade fever. Chest x-ray reveals an infiltrate in the lower lobe of the right lung. The patient is started on broad-spectrum antibiotics, including vancomycin, ceftriaxone, and azithromycin. Despite these measures, his condition worsens over the next several days. Bronchoscopy with bronchoalveolar lavage is performed. Mucicarmine staining of his bronchoalveolar fluid reveals the following on light microscopy: Which of the following is the most likely cause of this patient's condition?

Question

A 35-year-old man who received a kidney transplant one year ago comes to the emergency department with pleuritic chest pain and cough.  He is found to have a low-grade fever.  Chest x-ray reveals an infiltrate in the lower lobe of the right lung.  The patient is started on broad-spectrum antibiotics, including vancomycin, ceftriaxone, and azithromycin.  Despite these measures, his condition worsens over the next several days.  Bronchoscopy with bronchoalveolar lavage is performed.  Mucicarmine staining of his bronchoalveolar fluid reveals the following on light microscopy:  Which of the following is the most likely cause of this patient's condition?

Quizplus · Accepted Answer

Cryptococcus neoformans is a yeast that has an antiphagocytic polysaccharide capsule, a major virulence factor. The polysaccharide capsule appears as a clear, unstained zone with India ink and stains red with mucicarmine (as seen in this patient). Methenamine silver stain can identify the yeast forms, seen in tissue as round cells with narrow-based buds. C neoformans usually affects immunocompromised patients (eg, kidney transplantation patients on chronic immunosuppression). It is a neurotropic fungus that is transmitted via the respiratory route and most commonly presents with subacute or chronic meningoencephalitis. Cryptococcal lung disease can occasionally cause pneumonia-like symptoms, including cough with scant sputum production, pleuritic chest pain, dyspnea, and hemoptysis. Chest x-ray findings are nonspecific (eg, infiltrates, nodules). Diagnosis is usually confirmed by identifying Cryptococcus in sputum, bronchoalveolar washings, or tissue samples. (Choice A) Aspergillus fumigatus can cause pulmonary disease and invasive aspergillosis, most commonly in immunocompromised patients. However, microscopy typically shows septate hyphae. (Choice B) Blastomyces dermatitidis can cause both lung disease and disseminated mycosis. Its microscopic appearance in tissue is that of a round yeast with broad-based budding and a thick, doubly reflective wall. (Choice C) Candida albicans most commonly causes oropharyngeal, mucocutaneous, and esophageal disease. It rarely causes pneumonia. Microscopy typically shows budding yeast with pseudo-hyphae. (Choice D) Coccidioides immitis causes lung disease in immunocompetent individuals and disseminated mycosis in immunocompromised patients. In tissue samples, it appears as large, irregularly sized, thick-walled spherules that contain small, round endospores. (Choice F) Histoplasma capsulatum is a dimorphic fungus that causes tuberculosis-like pulmonary disease. It can also cause disseminated mycosis in immunocompromised patients. It is found intracellularly in tissue (within macrophages), appearing as small, ovoid, and budding yeast cells. (Choice G) Rhizopus species typically causes rhino-orbito-cerebral infection but can cause pulmonary disease, predominantly in immunocompromised patients. Histology typically shows broad hyphae with irregular branching and rare septations. Educational objective: Cryptococcus neoformans is the only pathogenic fungus that has a polysaccharide capsule. The capsule appears red on mucicarmine stain and as a clear unstained zone with India ink.

A 35-Year-Old Man Who Received a Kidney Transplant One Year