Respiratory · Year 1 · from Respiratory
Case 3: Pneumocystis jirovecii Pneumonia in HIV/AIDS
Case Presentation
A 34-year-old man with recently diagnosed HIV infection (not yet on antiretroviral therapy) presents with 3 weeks of progressive dyspnea, dry cough, and low-grade fevers. His CD4 count on diagnosis 1 month ago was 85 cells/microliter. On examination, he is tachypneic with respiratory rate 28/min. Oxygen saturation is 85% on room air, improving to only 90% on 6 L/min nasal cannula. Lung examination is surprisingly unremarkable despite his significant hypoxemia.
Chest X-ray shows bilateral diffuse interstitial infiltrates with a "ground-glass" pattern. CT chest confirms bilateral ground-glass opacities with characteristic sparing of the lung apices and periphery. LDH is markedly elevated at 580 U/L. Arterial blood gas on room air shows pH 7.46, PaCO2 30 mmHg, PaO2 52 mmHg with A-a gradient of 52 mmHg.
The clinical picture is classic for Pneumocystis jirovecii pneumonia (PCP): subacute onset over weeks, dry cough, exertional dyspnea, relatively normal lung exam despite severe hypoxemia, bilateral ground-glass infiltrates, and elevated LDH. PCP occurs almost exclusively in immunocompromised patients, particularly those with AIDS and CD4 less than 200 cells/microliter.
Induced sputum is obtained and tested with direct fluorescent antibody (DFA) staining, revealing P. jirovecii cysts. Bronchoscopy with BAL would be performed if induced sputum were negative, given the high clinical suspicion.
Treatment is initiated with high-dose trimethoprim-sulfamethoxazole (TMP-SMX). Given severe hypoxemia (PaO2 less than 70 mmHg on room air), adjunctive corticosteroids (prednisone) are added - this reduces mortality in moderate-to-severe PCP by blunting the inflammatory response as organisms die. He improves over 2 weeks and is discharged on TMP-SMX prophylaxis (to prevent recurrence while CD4 remains low) and antiretroviral therapy is initiated. Secondary prophylaxis continues until CD4 rises above 200 for at least 3 months.
Key Learning Points
- PCP presents subacutely (weeks) with dyspnea, dry cough, and hypoxemia disproportionate to exam findings
- Occurs in immunocompromised patients, especially AIDS with CD4 less than 200
- Chest imaging shows bilateral ground-glass infiltrates; LDH is typically elevated
- TMP-SMX is treatment of choice; adjunctive corticosteroids if PaO2 less than 70 mmHg on room air
- Primary prophylaxis with TMP-SMX indicated when CD4 less than 200