A 32-year-old woman from Mumbai presents to the emergency department with a 3-week history of fever, severe headache, and altered mental status. She has been on oral ciprofloxacin for 5 days without improvement. On examination, she is febrile (39.2°C), confused, and has neck stiffness. Fundoscopy reveals no papilledema. Cerebrospinal fluid analysis shows: protein 120 mg/dL, glucose 35 mg/dL (serum glucose 95 mg/dL), WBC 180 cells/μL (90% lymphocytes), Gram stain negative. Blood culture is negative. What is the most likely diagnosis?

Explanation

## Tuberculous Meningitis: The Most Likely Diagnosis ### Clinical Context **Key Point:** Tuberculous meningitis (TBM) is the most common cause of subacute/chronic meningitis with lymphocytic pleocytosis, low glucose, and elevated protein in a TB-endemic country like India. This presentation — 3-week fever, headache, altered mental status, neck stiffness, and the described CSF profile — is the classic textbook picture of TBM (Harrison's Principles of Internal Medicine, 21e, Ch. 177). ### Why This Case Fits Tuberculous Meningitis 1. **Subacute onset over 3 weeks** — TBM characteristically presents over days to weeks, unlike acute bacterial meningitis (hours to days) or viral meningitis (days). 2. **Mumbai (TB-endemic region)** — India accounts for ~26% of global TB burden; TBM is a leading cause of meningitis in this population. 3. **CSF profile:** - Protein 120 mg/dL — elevated, consistent with TBM (typically 100–500 mg/dL) - Glucose 35 mg/dL with serum glucose 95 mg/dL → CSF:serum ratio = 0.37 (<0.4) — hypoglycorrhachia, hallmark of TBM - WBC 180 cells/μL with 90% lymphocytes — lymphocytic pleocytosis, classic for TBM - Gram stain negative — expected in TBM (AFB smear positive in only 10–40%) 4. **Negative blood culture** — consistent with TBM; blood cultures are not expected to be positive in TBM. 5. **Failure of ciprofloxacin** — fluoroquinolones have limited anti-mycobacterial efficacy at standard doses and are not appropriate empiric therapy for TBM. 6. **No papilledema on fundoscopy** — does not exclude TBM; papilledema is present in only ~10% of TBM cases at presentation. ### CSF Profile Comparison | Parameter | TBM | Typhoid Encephalopathy | Bacterial Meningitis | Viral Meningitis | |---|---|---|---|---| | **Protein (mg/dL)** | 100–500 | 100–200 | 200–500 | 50–100 | | **Glucose** | Low (<0.4 ratio) | Low (<0.4 ratio) | Very low (<0.3) | Normal/mildly low | | **Cell count** | 50–500 | 50–500 | 100–10,000 | 50–500 | | **Predominance** | Lymphocytes | Lymphocytes | Neutrophils | Lymphocytes | | **Gram stain** | Negative | Negative | Positive (50–80%) | Negative | | **Duration** | Weeks–months | 2–3 weeks | Hours–days | Days | ### Why Typhoid Encephalopathy (Option C) Is Less Likely **Clinical Pearl:** While typhoid encephalopathy can cause CNS involvement with lymphocytic pleocytosis and low glucose, it is a diagnosis of exclusion in this context. Key arguments against it: - **True typhoid encephalopathy with meningitis is rare** — most CNS manifestations of enteric fever are encephalopathic (toxic/metabolic) rather than true meningitis with CSF pleocytosis and hypoglycorrhachia. - **CSF glucose is typically normal or mildly low** in typhoid encephalopathy; a CSF:serum ratio of 0.37 with frank hypoglycorrhachia is more characteristic of TBM or bacterial meningitis. - **No epidemiological clue** pointing specifically to enteric fever (no travel history, no rose spots, no relative bradycardia mentioned). - **TBM is far more prevalent** than typhoid encephalopathy as a cause of subacute meningitis in India. ### Differential Diagnosis Exclusion 1. **Bacterial meningitis (N. meningitidis) — Option A:** Would show neutrophilic pleocytosis, positive Gram stain, and acute (not 3-week) onset. Blood culture typically positive. 2. **Viral meningitis with superinfection — Option B:** CSF glucose is typically normal (ratio >0.4) in viral meningitis; protein usually <100 mg/dL. Self-limited course inconsistent with 3-week progressive illness. 3. **Typhoid encephalopathy — Option C:** Subacute meningitis with frank hypoglycorrhachia and lymphocytic pleocytosis is not the typical CSF pattern; TBM is a far more common and better-fitting diagnosis in this endemic setting. ### Management of TBM **High-Yield:** Standard anti-tubercular therapy (ATT) for TBM: - **Intensive phase (2 months):** HRZE (Isoniazid + Rifampicin + Pyrazinamide + Ethambutol) - **Continuation phase (7–10 months):** HR (Isoniazid + Rifampicin) - **Adjunctive dexamethasone** — reduces mortality and neurological sequelae (NEJM 2004; Harrison 21e) [cite: Harrison 21e Ch. 177; Park's Textbook of Preventive and Social Medicine, 26e]