A 32-year-old woman with known SLE (ANA+, anti-dsDNA+) on hydroxychloroquine and prednisolone presents with acute onset of severe headache, confusion, and a seizure. On examination, she is febrile (38.5°C), has neck stiffness, and a petechial rash on the trunk. CSF analysis shows: WBC 180/μL (85% lymphocytes), protein 120 mg/dL, glucose 35 mg/dL (serum glucose 90 mg/dL), Gram stain negative, bacterial culture negative. What is the most likely diagnosis?

Explanation

## Diagnosis: Tuberculous Meningitis (TBM) ### Clinical Context This patient has **known SLE on immunosuppressive therapy** (hydroxychloroquine + prednisolone), placing her at significantly elevated risk for **opportunistic infections**, including tuberculosis. The combination of subacute-to-acute onset of headache, confusion, seizure, fever, neck stiffness, and a characteristic CSF profile points strongly toward **tuberculous meningitis** rather than CNS lupus. ### CSF Profile Analysis | Parameter | Finding | Interpretation | |-----------|---------|----------------| | **WBC count** | 180/μL (85% lymphocytes) | Lymphocytic pleocytosis — classic for TBM | | **Protein** | 120 mg/dL | Elevated; TBM typically 100–500 mg/dL | | **Glucose** | 35 mg/dL (CSF:serum ratio 0.39) | **Hypoglycorrhachia** — ratio <0.4 is a hallmark of TBM | | **Gram stain/culture** | Negative | Expected in TBM; bacterial meningitis excluded | **Key Point:** The **CSF:serum glucose ratio of 0.39 (<0.4)** with **lymphocytic pleocytosis** and **elevated protein** is the classic triad of **tuberculous meningitis**. This pattern is NOT typical of aseptic meningitis due to CNS lupus, which usually shows a normal or only mildly reduced glucose. ### Why TBM Over CNS Lupus? - **Hypoglycorrhachia** (CSF glucose <45 mg/dL or ratio <0.5) is a hallmark of **granulomatous/infectious meningitis** (TB, fungal), NOT of lupus aseptic meningitis, which typically has **normal or near-normal CSF glucose**. - **Immunosuppression** (chronic corticosteroids) dramatically increases TB reactivation risk — this is a well-established clinical scenario (Harrison's Principles of Internal Medicine, 21st ed.). - **Petechial rash** in this context may reflect vasculitis from TBM or SLE systemic manifestation, but does not exclude TBM. - CNS lupus aseptic meningitis characteristically shows **normal glucose** and only mildly elevated protein; the degree of hypoglycorrhachia here is atypical for lupus meningitis. ### TBM Diagnostic Features (Harrison's / Park's Textbook of Preventive Medicine) - **CSF**: lymphocytic pleocytosis (100–500 cells/μL), protein 100–500 mg/dL, glucose <45 mg/dL (ratio <0.5) - **AFB smear**: positive in only 10–40% of cases — a negative Gram stain does NOT exclude TBM - **ADA (adenosine deaminase)**: elevated in CSF (>10 U/L) supports TBM - **CSF culture for Mycobacterium tuberculosis**: gold standard but takes weeks - **GeneXpert MTB/RIF on CSF**: rapid molecular confirmation ### Why Not the Other Options? - **CNS Lupus (A)**: Aseptic meningitis in SLE typically shows **normal CSF glucose**; hypoglycorrhachia strongly argues against this diagnosis. - **Bacterial Meningitis (C)**: Excluded by negative Gram stain and bacterial culture; bacterial meningitis also shows PMN predominance and usually protein >200 mg/dL. - **HSV-1 Meningitis (D)**: HSV encephalitis/meningitis shows lymphocytic pleocytosis but **normal glucose** and is confirmed by CSF PCR; hypoglycorrhachia is not a feature. ### Management 1. **Anti-tubercular therapy (ATT)**: HRZE (isoniazid, rifampicin, pyrazinamide, ethambutol) × 2 months, then HR × 7–10 months 2. **Adjunctive dexamethasone**: Reduces mortality and neurological sequelae in TBM (NEJM 2004; Thwaites et al.) 3. **Monitor for IRIS** (immune reconstitution inflammatory syndrome) if immunosuppression is modified 4. **Seizure management**: Levetiracetam or phenytoin 5. **Empiric coverage**: Maintain broad coverage until TBM confirmed; adjust SLE immunosuppression cautiously **Clinical Pearl:** In any SLE patient on chronic steroids presenting with meningitis and **low CSF glucose**, TBM must be the primary diagnosis until proven otherwise. The immunosuppressed state masks typical inflammatory signs and delays diagnosis — a high index of suspicion is essential (Harrison's Principles, 21st ed.).