A 38-year-old HIV-positive man (CD4 count 85 cells/µL) presents with fever, dry cough, and progressive dyspnoea over 3 weeks. CXR shows bilateral interstitial infiltrates. SpO2 88% on room air. LDH is 450 IU/L (elevated). What treatment regimen is indicated, and when should corticosteroids be added?
- A Fluconazole — PCP is fungal; no steroids needed
- B TMP-SMX (15-20 mg/kg/day of TMP component) for 21 days; add adjunctive corticosteroids if PaO2 < 70 mmHg or A-a gradient > 35 mmHg ✓
- C TMP-SMX only if PaO2 > 70 mmHg; withhold for moderate/severe disease
- D Pentamidine IV as first-line; TMP-SMX only for mild disease
Explanation
This presentation is classic Pneumocystis jirovecii pneumonia (PCP) — insidious dry cough, bilateral interstitial infiltrates, elevated LDH, and low CD4 (< 200 cells/µL). Treatment is high-dose TMP-SMX for 21 days. Adjunctive corticosteroids (prednisone 40 mg BD tapering) are indicated when PaO2 < 70 mmHg on room air or A-a gradient > 35 mmHg — this reduces risk of respiratory failure and mortality by dampening the inflammatory reaction during microbial killing. Corticosteroids must be started within 72 hours of antibiotics. Pentamidine is a second-line alternative only when TMP-SMX is contraindicated.
Reference: Harrison's Principles of Internal Medicine, 21st ed.
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Written and medically reviewed by the StethoPrep medical team.