A 32-year-old man with HIV infection (CD4 count 85 cells/µL) presents with fever, headache, and neck stiffness for 2 weeks. CSF analysis shows elevated protein (120 mg/dL), low glucose (25 mg/dL), and India ink stain is positive. Which clinical feature best distinguishes cryptococcal meningitis from tuberculous meningitis in this patient?

Explanation

## Distinguishing Cryptococcal from Tuberculous Meningitis ### Key Discriminating Feature **Key Point:** Positive India ink stain or cryptococcal antigen (CrAg) in CSF is pathognomonic for cryptococcal meningitis and definitively distinguishes it from tuberculous meningitis. ### Comparative CSF Findings | Feature | Cryptococcal Meningitis | Tuberculous Meningitis | |---------|------------------------|----------------------| | **India ink stain** | Positive (encapsulated yeast) | Negative | | **CrAg antigen** | Positive (highly sensitive) | Negative | | **Cell count** | Variable (10–500 cells/µL) | 100–500 cells/µL | | **Cell type** | Lymphocytic (may be minimal) | Lymphocytic (predominant) | | **Protein** | Elevated (50–200 mg/dL) | Markedly elevated (100–500 mg/dL) | | **Glucose** | Low (20–40 mg/dL) | Low (20–40 mg/dL) | | **Culture** | Grows on Sabouraud medium | Grows on Löwenstein medium (slow) | ### Clinical Pearl **Clinical Pearl:** In advanced HIV (CD4 <100), cryptococcal meningitis may present with minimal CSF pleocytosis ("acellular meningitis") because the immune response is profoundly suppressed. India ink or CrAg antigen becomes the diagnostic anchor. ### High-Yield Mnemonic **Mnemonic:** **CRYPTO** — **C**rAg antigen, **R**ound yeast, **Y**east in India ink, **P**ositive cultures on Sabouraud, **T**ortuous course (indolent), **O**pportunistic in CD4 <100. ### Why Other Features Are Non-Discriminatory - **CSF lymphocytic pleocytosis with elevated protein:** Both conditions present identically; this is NOT discriminatory. - **Subacute presentation:** Both cryptococcal and tuberculous meningitis present insidiously over weeks; no distinction. - **Low CSF glucose with elevated protein ratio:** Both share this pattern; not specific to either.