Pneumocystis jirovecii vs Cryptococcus
How to tell Pneumocystis jirovecii and Cryptococcus apart when a board question makes them look alike.
Pneumocystis is low-CD4 diffuse hypoxemic pneumonia; Cryptococcus is encapsulated yeast meningitis with high opening pressure.
Side by side
Pneumocystis causes subacute dry cough, dyspnea, hypoxemia, diffuse bilateral ground-glass infiltrates, and disease classically below CD4 200.
Cryptococcus causes subacute meningitis with headache, fever, high opening pressure, and encapsulated yeast, classically in advanced HIV or transplant patients.
Pneumocystis produces alveolar infection and impaired gas exchange in cellular immunodeficiency.
Cryptococcus is inhaled, survives through its polysaccharide capsule, and can disseminate to the CNS.
Elevated LDH, beta-D-glucan, BAL staining, severe A-a gradient, and diffuse ground-glass imaging support Pneumocystis.
Cryptococcal antigen, India ink halo, mucicarmine capsule staining, and high CSF opening pressure support Cryptococcus.
The trap
Both occur in immunocompromised hosts, so lung gas-exchange disease versus CNS capsule disease separates them.
The repair move
For opportunistic fungi, localize first: alveoli and oxygenation versus meninges and opening pressure.
Try a free question
CoreA 34-year-old man newly diagnosed with HIV has CD4 count 95 cells/uL and presents with 3 weeks of progressive dry cough and exertional dyspnea. Vital signs: respiratory rate 28, SpO2 88% on room air. Chest x-ray shows diffuse bilateral perihilar ground-glass infiltrates, and serum LDH is 720 U/L. Which organism is most likely?
Show answer and explanation
Answer: A. Pneumocystis jirovecii. Pneumocystis pneumonia in advanced HIV produces subacute hypoxemic dyspnea, diffuse bilateral ground-glass infiltrates, and elevated LDH; classically occurs at CD4 below 200 cells/uL.
Why the other choices are tempting
- B. Cryptococcus neoformans in HIV typically causes meningitis with high opening pressure and encapsulated yeast, not diffuse pulmonary ground-glass infiltrates.
- C. Mycobacterium tuberculosis in HIV may show atypical patterns but classically presents with upper lobe cavitation or lymphadenopathy, not diffuse perihilar ground-glass disease.
- D. Streptococcus pneumoniae causes lobar consolidation with rust-colored sputum and an acute presentation, not subacute hypoxemic ground-glass disease.
- E. CMV pneumonitis is uncommon outside transplant settings and would have distinct imaging plus owl-eye inclusions on biopsy.
Flashcards
Tap a card to flip it.
What CD4 threshold supports Pneumocystis pneumonia?
CD4 below 200 supports Pneumocystis pneumonia.
What imaging pattern supports Pneumocystis?
Diffuse bilateral ground-glass or interstitial infiltrates support Pneumocystis.
Quick answers
What is the fastest way to tell Pneumocystis jirovecii from Cryptococcus?
Pneumocystis is low-CD4 diffuse hypoxemic pneumonia; Cryptococcus is encapsulated yeast meningitis with high opening pressure.
What is the key clue for Pneumocystis jirovecii?
Pneumocystis causes subacute dry cough, dyspnea, hypoxemia, diffuse bilateral ground-glass infiltrates, and disease classically below CD4 200.
What is the key clue for Cryptococcus?
Cryptococcus causes subacute meningitis with headache, fever, high opening pressure, and encapsulated yeast, classically in advanced HIV or transplant patients.
What is the common trap with Pneumocystis jirovecii vs Cryptococcus?
Both occur in immunocompromised hosts, so lung gas-exchange disease versus CNS capsule disease separates them.