A 32-year-old woman from Mumbai presents with a 3-day history of fever (38.5°C), headache, myalgia, and mild neck stiffness. She denies photophobia. On examination, she is alert and oriented, with no focal neurological deficit. CSF analysis shows: WBC 85/μL (60% lymphocytes, 40% monocytes), protein 65 mg/dL, glucose 62 mg/dL (serum glucose 100 mg/dL), Gram stain negative, culture negative at 24 hours. What is the most likely diagnosis?

Explanation

## Clinical Presentation & CSF Profile **Key Point:** The constellation of mild symptoms, **lymphocytic predominance in CSF** (60%), **normal-to-mildly-elevated glucose** (CSF:serum ratio ~0.62), **negative Gram stain and culture**, and **subacute course** (3 days) are classic for **viral meningitis**. ## Diagnostic Features of Viral Meningitis | Feature | Viral Meningitis | Bacterial Meningitis | TB Meningitis | |---------|------------------|----------------------|---------------| | **Onset** | Acute to subacute (hours–days) | Fulminant (hours) | Insidious (days–weeks) | | **CSF WBC** | 50–500/μL | 500–10,000/μL | 100–500/μL | | **Cell type** | Lymphocytes (early: neutrophils) | Neutrophils (>80%) | Lymphocytes (>50%) | | **CSF glucose** | Normal or mildly ↓ (>40 mg/dL) | **Very low (<40 mg/dL)** | **Very low (<40 mg/dL)** | | **CSF:serum glucose** | >0.4 | <0.4 | <0.4 | | **Protein** | Mildly ↑ (50–100 mg/dL) | Markedly ↑ (>200 mg/dL) | Markedly ↑ (>200 mg/dL) | | **Gram stain** | Negative | Positive in 60–80% | Negative | | **Culture** | Negative (viral PCR positive) | Positive in 80% | Positive in 50% (slow growth) | **High-Yield:** Viral meningitis is the most common form of aseptic meningitis in immunocompetent adults. Enteroviruses (Coxsackievirus, Echovirus) account for 70–80% of cases in India. ## Why Viral Meningitis? **Clinical Pearl:** This patient has: 1. **Subacute presentation** with mild symptoms (no photophobia, alert, no focal deficits) 2. **Lymphocytic CSF** (60% lymphocytes) — hallmark of viral infection 3. **Preserved CSF glucose** (62 mg/dL, CSF:serum ratio 0.62) — bacterial and TB meningitis cause severe hypoglycorrhachia 4. **Negative cultures at 24 hours** — rules out bacterial meningitis 5. **No systemic signs of TB** (no weight loss, night sweats, or chronic illness mentioned) ## Management **Key Point:** Viral meningitis is self-limited in immunocompetent hosts. Treatment is supportive (analgesia, hydration, NSAIDs). Antibiotics should be **discontinued** once bacterial meningitis is excluded by negative Gram stain and culture. [cite:Harrison 21e Ch 139; Robbins 10e Ch 28]