What is the approach to detecting meningitis, particularly in pediatric patients?

How to Detect Meningitis in Pediatric Patients

The diagnosis of bacterial meningitis rests fundamentally on cerebrospinal fluid examination obtained via lumbar puncture, which should be performed emergently in all suspected cases unless specific contraindications exist, with blood cultures drawn simultaneously and empiric antibiotics initiated within 1 hour of presentation. 1, 2

Clinical Presentation by Age Group

Neonates (≤28 days)

• Present with nonspecific symptoms making diagnosis particularly challenging 3
• Irritability, poor feeding, respiratory distress, pale or marbled skin, and abnormal tone (hyper- or hypotonia) 3
• Fever present in only 6-39% of cases 3
• Seizures occur in 9-34% of neonatal cases 3
• Classic meningeal signs are typically absent in this age group 3

Infants and Young Children (1 month to 5 years)

• Fever is the most common symptom (92-93% of cases) 3
• Vomiting occurs in 55-67% of cases 3
• Headache reported in only 2-9% of children under 1 year, but 75% over age 5 3
• Neck stiffness present in 40-82% of cases 3
• Altered mental status in 13-56% of cases 3
• Bulging fontanel when present has high predictive value (likelihood ratio 8.0) 4

Older Children and Adolescents

• Present more similarly to adults with classic triad features 3
• Headache becomes more prominent (75% in children >5 years) 3
• Neck stiffness and meningeal signs more reliable 3

Critical Diagnostic Algorithm

Step 1: Initial Clinical Assessment

Do NOT rely on clinical signs alone to rule out meningitis - the classic triad of fever, neck stiffness, and altered mental status is present in only 41-51% of cases 3, 2

Clinical signs with highest predictive value when present: 4

• Bulging fontanel (LR 8.0)
• Neck stiffness (LR 7.7)
• Toxic or moribund appearance (LR 5.8)
• Seizures outside febrile convulsion age range (LR 4.4)
• Kernig sign (LR 3.5)
• Brudzinski sign (LR 2.5)

Critical pitfall: Absence of fever does NOT rule out meningitis (LR 0.70), and absence of meningeal signs only modestly reduces likelihood (LR 0.41) 4

Step 2: Determine Need for CT Before Lumbar Puncture

Obtain non-contrast head CT immediately before lumbar puncture if ANY of the following are present: 1, 2

• Immunocompromised state
• History of CNS disease (mass lesion, stroke, focal infection)
• New-onset seizure
• Papilledema
• Altered consciousness (Glasgow Coma Scale <11)
• Focal neurologic deficits

CT has 98-100% sensitivity for detecting contraindications to LP within first 6-12 hours and 90% specificity for identifying dangerous mass effect 2

Step 3: Immediate Management Protocol

Within the first hour of presentation: 2

1. Draw blood cultures immediately
2. If CT required, obtain stat non-contrast head CT
3. Initiate empiric antibiotics BEFORE lumbar puncture if any delay anticipated - do not wait for imaging or LP results 2
4. Administer dexamethasone with or just before first antibiotic dose 1, 2

Step 4: Lumbar Puncture and CSF Analysis

Perform LP emergently once herniation risk excluded 1, 2

Essential CSF studies to order: 1

• Opening pressure (expect >200-500 mm H₂O in bacterial meningitis) 1
• Cell count with differential (expect 1000-5000 WBC/mm³ with 80-95% neutrophils) 1
• Glucose (expect <40 mg/dL; CSF:serum ratio <0.4) 1, 2
• Protein (expect elevated >45 mg/dL) 1, 2
• Gram stain (60-90% sensitive, 97% specific) 1
• Bacterial culture (70-85% positive if no prior antibiotics) 1
• PCR for S. pneumoniae, N. meningitidis, H. influenzae (79-100% sensitive, essential if prior antibiotics given) 1

Critical diagnostic yields: 1

• Gram stain sensitivity: 90% for pneumococcal, 70-90% for meningococcal, 50% for H. influenzae
• Culture positivity drops from 88% to 70% if antibiotics given before LP 1
• PCR detects 33-57% of cases missed by conventional methods 1

Step 5: Imaging for Complications

MRI with and without IV contrast is superior to CT for detecting: 1

• Meningeal enhancement (use T2 FLAIR and post-contrast T1 sequences) 1
• Vasogenic edema (T2 FLAIR sensitive) 1
• Cytotoxic edema (diffusion-weighted imaging) 1
• Subdural or epidural empyema 1
• Brain abscess 1
• Venous sinus thrombosis (add MRV if suspected) 1

CT has poor sensitivity (23% in one study) compared to MRI for detecting pediatric encephalitis and meningitis complications 1

Common Pitfalls to Avoid

1. Never delay antibiotics waiting for imaging or LP - mortality increases significantly with treatment delays in bacterial meningitis (baseline mortality 20-30%) 2

2. Do not assume absence of classic signs rules out meningitis - sensitivity of neck stiffness is only 51% in children, Kernig sign 53%, Brudzinski sign 66% 3, 4

3. Do not perform LP before CT in patients with altered consciousness or focal deficits - risk of cerebral herniation 1, 2

4. Do not rely on latex agglutination tests - sensitivity only 7-9% in patients who received antibiotics before LP, adds minimal value beyond Gram stain 1

5. Do not skip PCR testing - essential for diagnosis when antibiotics given before LP, detects 33-57% of cases missed by culture alone 1

Empiric Antibiotic Regimen

Initiate within 1 hour: 2

• Ceftriaxone 50-100 mg/kg IV (max 2-4g) for suspected pneumococcal/meningococcal meningitis
• Add vancomycin for pneumococcal coverage in areas with resistant strains
• Add ampicillin 200-300 mg/kg/day divided every 6 hours if Listeria suspected (neonates, immunocompromised) 5
• Dexamethasone 0.15 mg/kg IV given with or just before first antibiotic dose to reduce mortality and neurological sequelae 2