A 48-year-old homeless man is brought to the emergency department after being found unresponsive on the sidewalk. Medical history is unknown. Temperature is 38.3 C (101 F), blood pressure is 116/70 mm Hg, pulse is 108/min, and respirations are 26/min. Oxygen saturation is 88% on 100% oxygen via face mask. The patient is ill-appearing, thin, and disheveled with poor dentition. There are a few white patches on the oral mucosa, but no skin rash is present. Lung auscultation reveals bilateral crackles. There are healed abdominal scars from a previous surgery. The abdomen is soft with no hepatomegaly or splenomegaly. Chest x-ray reveals bilateral interstitial infiltrates. A silver-stained bronchoalveolar lavage specimen is shown in the image.
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Which of the following most likely predisposed this patient to his current lung condition?
This homeless patient has hypoxia, bilateral interstitial infiltrates, and a positive silver stain indicating likely Pneumocystis pneumonia (PCP), an atypical fungal infection caused by the opportunistic pathogen P jirovecii. Inhalation of the organism leads to inoculation of the alveolar space. Healthy individuals rarely develop symptoms as alveolar monocytes and macrophages are stimulated by the cell-mediated immune response to rapidly clear the organism. However, patients with impaired cell-mediated immunity, particularly those with untreated AIDS (CD4 count <200/mm3), often cannot eliminate the pathogen.
PCP typically manifests with slowly worsening pulmonary symptoms (eg, cough, dyspnea), hypoxia, and chest x-ray evidence of a diffuse, bilateral interstitial infiltrate. Because P jirovecii cannot be cultured, diagnosis is made by identifying the organism in respiratory secretions using specialized stains (eg, methenamine silver stain).
This patient also has oral pharyngeal candidiasis (white patches on the oral mucosa), an opportunistic infection often seen in those with impaired cell-mediated immunity.
(Choice A) Aspiration pneumonia is common in patients who have impaired levels of consciousness. It usually presents with cough productive of foul-smelling sputum, dyspnea, fever, and a lobar infiltrate on chest x-ray. Most cases are caused by a mixture of anaerobic organisms.
(Choices B and E) Cigarette smoking impairs the ability of the cilia to clear mucus, which can lead to recurrent bacterial pneumonia. Patients with splenectomy are at increased risk for fulminant bacterial infections, particularly with encapsulated organisms such as Streptococcus pneumoniae. Bacterial pneumonia usually presents with cough productive of sputum, dyspnea, fever, and a lobar infiltrate on chest x-ray. The presence of diffuse interstitial infiltrates and a positive silver stain make PCP more likely.
(Choice C) The humoral antibody response is important for the elimination of pathogenic bacterial and viral infections. Although viral pneumonia can cause bilateral interstitial infiltrates, viruses are not identified on silver stain.
Educational objective:
Pneumocystis pneumonia is an atypical fungal infection seen primarily in those with impaired cell-mediated immunity (eg, advanced AIDS). Manifestations often include slowly worsening pulmonary symptoms, hypoxia, and bilateral interstitial infiltrates on chest x-ray. The cystic organism can be visualized using silver stain of respiratory secretions.