Step by Step
Cn
Cryptococcus neoformans — found in pigeon droppings and soil
Cryptococcus neoformans is an encapsulated yeast, commonly found in pigeon droppings and soil. Its defining feature is a large polysaccharide capsule, which is antiphagocytic — it physically resists being engulfed by immune cells, helping the organism evade clearance.
Ink
India ink stain — visualizing the capsule
On India ink staining, Cryptococcus appears as a yeast cell surrounded by a clear halo — the capsule excluding the ink particles. This classic staining pattern is a quick way to visually identify the organism.
Ag
Latex agglutination — the more sensitive test
While India ink staining is the classic visual test, latex agglutination (detecting the capsular antigen directly in CSF) is actually more sensitive and is the preferred diagnostic test when available. CSF findings also classically show a very high opening pressure — sometimes described as producing a "soap bubble" appearance on MRI.
Tx
Treatment — induction then lifelong maintenance
Treatment happens in two phases: induction with amphotericin B plus flucytosine for about two weeks, followed by fluconazole maintenance therapy — which, in AIDS patients, continues lifelong (or until sustained immune reconstitution) rather than for a fixed course.
A patient with AIDS and a CD4 count of 60 develops a severe headache; CSF shows a markedly elevated opening pressure and is India ink positive — this is cryptococcal meningitis, requiring induction therapy followed by lifelong fluconazole maintenance.
Applied Walkthrough
1
A patient with AIDS and a CD4 count of 60 presents with a severe headache and altered mental status.
2
A lumbar puncture reveals a markedly elevated opening pressure, and India ink staining of the CSF shows yeast cells surrounded by a clear halo.
3
Ask: what's the diagnosis, and how should it be managed? This is cryptococcal meningitis — the CD4 count well below 100, along with the India ink findings and elevated pressure, confirm it.
4
Beyond antifungal therapy (induction with amphotericin B plus flucytosine, then fluconazole maintenance), the elevated opening pressure itself needs active management — repeated large-volume lumbar punctures or, in refractory cases, a shunt — since untreated elevated pressure can itself cause permanent neurological damage independent of the infection.
Exam Application
Exams test the CD4 threshold associated with cryptococcal meningitis (below 100), the diagnostic tests (India ink for visual identification, latex agglutination as the more sensitive antigen test), and the two-phase treatment structure — induction with amphotericin B plus flucytosine, followed by lifelong fluconazole maintenance in AIDS patients.
⚠ Common Trap
The most common trap is treating cryptococcal meningitis exactly like bacterial meningitis and forgetting the elevated CSF opening pressure requires its own separate, active management (serial large-volume LPs or a shunt) — untreated elevated pressure can cause permanent damage even if the infection itself is being appropriately treated with antifungals.
✓ Quick Self-Check
1. What environmental sources is Cryptococcus neoformans associated with?
Pigeon droppings and soil.
Tap to reveal / hide
2. What makes Cryptococcus resistant to being engulfed by immune cells?
Its large polysaccharide capsule, which is antiphagocytic.
Tap to reveal / hide
3. What does India ink staining show, and what is a more sensitive alternative test?
India ink shows a clear halo (the capsule) around the yeast cell; latex agglutination, which detects capsular antigen in CSF, is more sensitive.
Tap to reveal / hide
4. At what CD4 count does cryptococcal meningitis classically occur?
Below 100.
Tap to reveal / hide
5. What is the treatment structure for cryptococcal meningitis in an AIDS patient?
Induction with amphotericin B plus flucytosine for about two weeks, followed by fluconazole maintenance therapy continued lifelong.
Tap to reveal / hide