A 32-year-old man with HIV/AIDS (CD4 count 45 cells/μL) presents with fever, headache, and neck stiffness. CSF analysis shows lymphocytic pleocytosis with low glucose and elevated protein. India ink stain of CSF is positive. What is the most common cause of meningitis in this patient?

Explanation

## Most Common Cause of Meningitis in Advanced HIV/AIDS **Key Point:** Cryptococcal meningitis is the most common cause of meningitis in patients with CD4 count <100 cells/μL, accounting for 60–70% of meningitis cases in this population. ### Clinical Presentation - Subacute to chronic meningitis (develops over days to weeks) - Fever, headache, neck stiffness (though neck stiffness may be absent) - India ink stain positive in 50–80% of cases - CSF shows lymphocytic pleocytosis with low glucose and elevated protein - Cryptococcal antigen (CrAg) in serum and CSF is highly sensitive and specific ### Pathophysiology - *Cryptococcus neoformans* is an encapsulated yeast found ubiquitously in soil and bird droppings - Inhaled → primary pulmonary infection → dissemination to CNS in immunocompromised hosts - CD4 count <100 cells/μL is the critical threshold for disseminated disease ### Diagnostic Approach | Test | Sensitivity | Specificity | Notes | |------|-------------|-------------|-------| | India ink stain | 50–80% | High | Positive in this case | | CSF CrAg | 90–100% | 99% | Gold standard | | Serum CrAg | 95–100% | 99% | Positive in >90% of CNS disease | | Culture | 90% | 100% | Takes 1–2 weeks | ### Management 1. **Induction:** Amphotericin B deoxycholate (0.7–1 mg/kg/day IV) + Flucytosine (100 mg/kg/day in 4 divided doses) for 2 weeks 2. **Consolidation:** Fluconazole 400 mg/day for 8 weeks 3. **Maintenance:** Fluconazole 200 mg/day until CD4 count >100 cells/μL for ≥3 months on ART **High-Yield:** CrAg screening (serum ± CSF) should be performed in ALL patients with CD4 <100 cells/μL, even if asymptomatic. Early detection and treatment of asymptomatic cryptococcemia prevents meningitis. **Clinical Pearl:** Immune reconstitution inflammatory syndrome (IRIS) can occur 2–12 weeks after ART initiation, manifesting as worsening meningitis despite appropriate antifungal therapy. Manage with corticosteroids and continuation of antifungal therapy.