What is the likely diagnosis and recommended empiric therapy for a patient whose cerebrospinal fluid shows a total leukocyte count of 45 cells/µL, 83% polymorphonuclear cells, and elevated globulin?

Acute Bacterial Meningitis

This CSF profile indicates acute bacterial meningitis, and you must initiate empiric antimicrobial therapy with vancomycin plus either cefotaxime or ceftriaxone immediately, along with dexamethasone, within one hour of presentation.

Diagnosis

The CSF findings are highly consistent with bacterial meningitis 1:

• TLC 45 cells/µL with 83% polymorphonuclear cells represents the classic neutrophilic pleocytosis of bacterial infection
• Positive globulin indicates elevated CSF protein, another hallmark finding
• While the absolute cell count is relatively modest, bacterial meningitis typically shows 1000-5000 cells/mm³ but can range from 100 to >10,000 cells/mm³ 1
• Neutrophil predominance of 80-95% is characteristic of bacterial meningitis 1, 2

Critical Context

Approximately 10% of bacterial meningitis cases present with lymphocyte predominance, and some patients (particularly neonates and immunocompromised) may have completely normal CSF initially 1, 2. However, your patient's 83% polymorphonuclear predominance strongly supports bacterial etiology.

Immediate Management Algorithm

Step 1: Blood Cultures and Empiric Therapy (Within 1 Hour)

Before or immediately after lumbar puncture 1, 3:

1. Obtain blood cultures
2. Start dexamethasone (adjunctive therapy - Grade A recommendation) 3
3. Initiate empiric antibiotics immediately - delay increases morbidity and mortality 1

Step 2: Empiric Antibiotic Selection

The regimen depends on patient age and risk factors 1:

• Adults without specific risk factors: Vancomycin + (ceftriaxone OR cefotaxime)
• Children ≥1 month: Vancomycin + (ceftriaxone OR cefotaxime) 1
• Add ampicillin if: Age >50 years, immunocompromised, or concern for Listeria monocytogenes (gram-positive bacilli on Gram stain) 1

Step 3: Additional Diagnostic Workup

While awaiting culture results 1, 2:

• CSF Gram stain (60-90% sensitive, 97% specific) - if positive, allows targeted therapy
• CSF glucose and protein - expect glucose <40 mg/dL or CSF:serum ratio <0.4
• CSF lactate if available (better diagnostic accuracy than WBC count, especially with prior antibiotics) 2
• PCR for common pathogens (S. pneumoniae, N. meningitidis, H. influenzae) - particularly valuable if cultures negative 2

Common Pitfalls to Avoid

1. Never delay antibiotics for imaging or lumbar puncture - if CT needed first (immunocompromised, focal deficits, altered consciousness, new seizures, papilledema), give antibiotics immediately after blood cultures 1

2. Don't be falsely reassured by modest cell counts - 5% of pneumococcal meningitis cases have <10 cells/mm³ 2

3. Prior antibiotics reduce culture yield but don't eliminate pleocytosis - CSF findings (elevated WBC, low glucose, high protein) remain diagnostic 1

4. Lymphocytic predominance doesn't exclude bacterial meningitis - consider partially treated bacterial meningitis, Listeria, tuberculosis, or early-phase infection 1, 4, 5

Why This Matters for Mortality

Bacterial meningitis carries high mortality (15-30%) and morbidity rates 3. The ESCMID guideline emphasizes starting treatment within one hour because each hour of delay increases risk of death and neurological sequelae 3. Your patient's neutrophilic CSF profile demands immediate action - this is not a "wait and see" situation.

The combination of vancomycin plus third-generation cephalosporin covers the most common pathogens (S. pneumoniae, N. meningitidis, H. influenzae) including drug-resistant strains 1, 3. Dexamethasone reduces mortality and neurological complications when given with or before the first antibiotic dose 3.