MENINGITIS - ICUNOTES

MENINGITIS

Meningitis = inflammation of the leptomeninges (pia + arachnoid) and CSF within subarachnoid space.

Often part of a spectrum:
→ Meningitis (meninges)
→ Encephalitis (brain parenchyma)
→ Meningoencephalitis (both)

ETIOLOGY

CATEGORY / RISK GROUP	COMMON CAUSES
Neonates (<1 month)	• Group B Streptococcus (most common) • Escherichia coli • Listeria monocytogenes
Infants (1–3 months)	• Streptococcus pneumoniae • Neisseria meningitidis • Haemophilus influenzae type b • Group B Streptococcus
Children & Adolescents	• Neisseria meningitidis (most common) • Streptococcus pneumoniae • Haemophilus influenzae type b (↓ due to vaccination)
Adults (18–50 yrs)	• Streptococcus pneumoniae (most common) • Neisseria meningitidis
Elderly (>50 yrs)	• Streptococcus pneumoniae • Listeria monocytogenes • Gram-negative bacilli (e.g., Escherichia coli)
Post-neurosurgery / head trauma	• Staphylococcus aureus • Coagulase-negative staphylococci (e.g., Staphylococcus epidermidis) • Pseudomonas aeruginosa
CSF shunt / device-related	• Staphylococcus epidermidis • Staphylococcus aureus
Immunocompromised (HIV, steroids, chemo)	• Listeria monocytogenes • Mycobacterium tuberculosis • Cryptococcus neoformans
HIV (advanced)	• Cryptococcus neoformans (most common) • Mycobacterium tuberculosis
Basilar skull fracture / CSF leak	• Streptococcus pneumoniae
Nosocomial meningitis	• Pseudomonas aeruginosa • Acinetobacter baumannii • Staphylococci
Viral (aseptic meningitis)	• Enteroviruses (most common) • Herpes simplex virus • Varicella zoster virus • Mumps virus
Tuberculous meningitis	• Mycobacterium tuberculosis
Fungal meningitis	• Cryptococcus neoformans (most common) • Candida albicans • Aspergillus
Parasitic (rare)	• Naegleria fowleri (primary amebic meningoencephalitis) • Toxoplasma gondii (mainly encephalitis)

Most common overall (adults): Streptococcus pneumoniae
Young adults (hostel/military): Neisseria meningitidis
Elderly/immunocompromised: Always cover Listeria monocytogenes
HIV: Think Cryptococcus neoformans
India setting: TB meningitis = Mycobacterium tuberculosis
Post-neurosurgery: Think Staph + Pseudomonas

PATHOPHYSIOLOGY

Nasopharyngeal colonization
Hematogenous spread → crosses blood-brain barrier
Multiplication in CSF (low immunity)
Cytokine cascade:

TNF-α, IL-1 → inflammation
↑ BBB permeability

Consequences:

Cerebral edema
↑ ICP
↓ cerebral perfusion
Hydrocephalus
Vasculitis → infarcts

CLINICAL FEATURES

Classical triad (only ~50%)

Fever
Neck stiffness
Altered sensorium

Other symptoms

Headache (severe, diffuse)
Vomiting (projectile)
Photophobia
Seizures
Focal deficits (late)
Rash → meningococcemia

Neonates

Poor feeding
Irritability / lethargy
Bulging fontanelle
Hypothermia

MENINGEAL SIGNS(Low sensitivity but high specificity)

Feature	Kernig Sign	Brudzinski Sign
Maneuver	Knee extension with hip flexed	Neck flexion
Positive response	Pain/resistance in knee extension	Hip + knee flexion
Mechanism	Nerve root stretch	Reflex reduction of meningeal stretch

RED FLAGS (SEVERE DISEASE)

GCS ↓
Seizures
Papilledema
Focal deficits
Shock
Purpuric rash → meningococcemia

DIAGNOSIS

INITIAL EMERGENCY APPROACH

If meningitis is suspected → DO NOT delay antibiotics

Immediate Actions

Blood cultures ×2 (before antibiotics)
Start empiric antibiotics ± dexamethasone
Then proceed to imaging/LP depending on safety

WHEN TO DO CT BEFORE LUMBAR PUNCTURE

CT brain BEFORE LP if ANY of the following (IDSA criteria):

Indication	Reason
Altered consciousness	Risk of herniation
Focal neurological deficit	Mass lesion
New-onset seizures	Intracranial pathology
Papilledema	Raised ICP
Immunocompromised	Space-occupying lesion risk
Known CNS lesion	Risk of herniation

If NONE present → LP immediately (no CT delay)

LUMBAR PUNCTURE (GOLD STANDARD)

CSF OPENING PRESSURE

Type	Opening Pressure
Normal	6–20 cm H₂O
Bacterial	↑↑ (>25 cm)
TB	↑
Fungal	↑↑
Viral	Normal / mildly ↑

CSF ANALYSIS

Parameter	Bacterial	Viral	TB	Fungal
Appearance	Turbid	Clear	Slightly turbid	Clear/slightly cloudy
Cells	↑↑ (1000–5000)	↑ (50–1000)	↑ (100–500)	↑ (50–500)
Type	Neutrophils	Lymphocytes	Lymphocytes	Lymphocytes
Protein	↑↑ (>100 mg/dL)	Mild ↑	↑↑	↑
Glucose	↓ (<40 mg/dL)	Normal	↓	↓
CSF:Serum glucose	<0.4	Normal	<0.4	<0.5
Lactate	↑↑ (>3.5 mmol/L)	Normal	↑	↑

MICROBIOLOGICAL TESTS

1. Gram Stain

Rapid, bedside
Sensitivity: 60–90% (before antibiotics)

2. CSF Culture (Gold standard for organism)

Sensitivity ↓ after antibiotics

3. PCR (VERY HIGH YIELD)

Detects:HSV,Enterovirus,TB,Pneumococcus, meningococcus

Best test when prior antibiotics given

SPECIAL TESTS

Tubercular Meningitis

CSF ADA ↑
PCR for TB (GeneXpert)
AFB stain (low sensitivity)

Fungal

India ink (Cryptococcosis)
Cryptococcal antigen (very sensitive)

BLOOD TESTS

CBC → leukocytosis
CRP / Procalcitonin ↑ (bacterial)
Blood cultures (positive in 50–70%)
Electrolytes → SIADH (common in meningitis)

IMAGING

CT Brain

Rule out:

Mass lesion
Hydrocephalus
Cerebral edema

MRI Brain (more sensitive)

Basal meningeal enhancement → TB
Temporal lobe involvement → HSV
Abscess / complications

ADVANCED DIAGNOSTIC MARKERS

CSF LACTATE

3.5 mmol/L → strongly suggests bacterial meningitis

PROCALCITONIN

Elevated in bacterial
Helps differentiate viral vs bacterial

CSF PCR PANEL (Multiplex)

Rapid diagnosis (<2 hours)
Detects multiple organisms simultaneously

DIFFERENTIAL DIAGNOSIS

Condition	Key Difference
Encephalitis	Prominent altered sensorium + focal signs
Subarachnoid hemorrhage	RBCs in CSF
Brain abscess	Focal deficits + ring lesion
Tuberculoma	Chronic + focal lesion
Migraine	No CSF changes

WHEN TO REPEAT LP

No improvement after 48–72 hrs
Suspected resistant organism
TB meningitis monitoring

MANAGEMENT

1. INITIAL APPROACH

Start empiric antibiotics immediately → do NOT delay for imaging or LP (unless contraindications present)

Stepwise approach:

Airway, Breathing, Circulation (ABCs)
Blood cultures (×2 sets) before antibiotics (if no delay)
Start:

Empiric antibiotics
Adjunctive dexamethasone

Decide on LP vs CT-first strategy

2. EMPIRICAL ANTIBIOTIC THERAPY

Must cover:

Streptococcus pneumoniae
Neisseria meningitidis
± Listeria monocytogenes

1. EMPIRIC ANTIBIOTIC THERAPY

Clinical Scenario	Drug + Dose + Duration
Adults (18–50 yrs)	Ceftriaxone 2 g IV q12h + Vancomycin 15–20 mg/kg IV q8–12h (target trough 15–20 µg/mL) → Duration: until pathogen identified
>50 yrs / Immunocompromised / Alcoholic	Ceftriaxone + Vancomycin + Ampicillin 2 g IV q4h (for Listeria monocytogenes)
Post-neurosurgery / Head trauma / CSF shunt	Vancomycin + Cefepime 2 g IV q8h OR Ceftazidime 2 g IV q8h OR Meropenem 2 g IV q8h (covers Pseudomonas aeruginosa)
Severe β-lactam allergy	Vancomycin + Moxifloxacin 400 mg IV OD ± TMP-SMX 5 mg/kg (TMP) IV q6–8h (Listeria cover)

Add empiric antiviral if encephalitis cannot be ruled out

Indications to START Acyclovir:

Altered mental status / confusion
Behavioral changes
Focal neurological deficits
Seizures
Temporal lobe signs

2. TARGETED ANTIBIOTIC THERAPY

Organism	Drug + Dose + Duration
Streptococcus pneumoniae	Ceftriaxone 2 g IV q12h ± Vancomycin → De-escalate if sensitive → 10–14 days
Neisseria meningitidis	Ceftriaxone 2 g IV q12h OR Penicillin G 4 million units IV q4h → 5–7 days
Haemophilus influenzae	Ceftriaxone 2 g IV q12h → 7–10 days
Listeria monocytogenes	Ampicillin 2 g IV q4h ± Gentamicin 5–7 mg/kg/day → ≥21 days
Gram-negative bacilli	Cefepime 2 g IV q8h OR Meropenem 2 g IV q8h → 21 days
MRSA / Staphylococcus	Vancomycin (target trough 15–20) ± Rifampicin 600 mg/day → 10–14 days

3. ANTIVIRAL THERAPY

Indication / Virus	Drug + Dose + Duration
Suspected Herpes simplex encephalitis (HSV-1/2)	Acyclovir 10 mg/kg IV q8h (adjust for renal function) → 14–21 days
Varicella-zoster virus (VZV)	Acyclovir 10–15 mg/kg IV q8h → 10–14 days
CMV (immunocompromised)	Ganciclovir 5 mg/kg IV q12h ± Foscarnet → 2–3 weeks
Enteroviral meningitis	Usually supportive (no antiviral required)

4. ANTIFUNGAL THERAPY

Organism	Drug + Dose + Duration
Cryptococcal meningitis	Induction: Amphotericin B (liposomal 3–5 mg/kg/day IV) + Flucytosine 25 mg/kg PO q6h → 2 weeks Consolidation: Fluconazole 400–800 mg/day → 8 weeks Maintenance: Fluconazole 200 mg/day → ≥1 year (HIV)
Candida meningitis	Amphotericin B ± Flucytosine → then Fluconazole → several weeks
Aspergillus	Voriconazole 6 mg/kg IV q12h × 2 doses → then 4 mg/kg q12h → prolonged
Mucormycosis	Amphotericin B (liposomal 5 mg/kg/day) → surgical debridement + step-down posaconazole

Fungal meningitis is rare in immunocompetent patients

High-risk patients are

HIV/AIDS (CD4 <100)
Chronic steroid use
Organ transplant
Malignancy / chemotherapy
Uncontrolled diabetes

DURATION OF THERAPY

Organism	Duration
Meningococcus	5–7 days
Pneumococcus	10–14 days
H. influenzae	7–10 days
Listeria	≥21 days
Gram-negative bacilli	21 days

ADJUNCTIVE DEXAMETHASONE

Mechanism:

↓ Inflammatory cytokines → ↓ cerebral edema → ↓ complications

Regimen:

Dexamethasone 0.15 mg/kg IV q6h × 4 days
Start BEFORE or with first antibiotic dose

Indications:

Strong evidence: Pneumococcal meningitis
Continue only if pneumococcus confirmed

Benefits:

↓ Mortality
↓ hearing loss
↓ neurological sequelae

MANAGEMENT OF RAISED ICP

Measures:

Head elevation (30°)
Maintain:

PaCO₂: 35–40 mmHg
MAP adequate → CPP >60 mmHg

Osmotherapy:

Mannitol 0.25–1 g/kg
Hypertonic saline (3%)

Avoid hypotension, hypoxia

Avoid:

Routine hyperventilation (except herniation)
Excess fluids

CHEMOPROPHYLAXIS

Start AS EARLY AS POSSIBLE
Ideally within 24 hours of diagnosis
Benefit decreases after:

>14 days (meningococcal)

High-risk contacts:

Household members
Dormitory/hostel residents
Intimate partners
Childcare contacts
Direct exposure to oral secretions:

Kissing
Mouth-to-mouth resuscitation
Intubation without protection

REQUIRED

Neisseria meningitidis (MENINGOCOCCAL) → MANDATORY
Haemophilus influenzae type b → SELECTIVE

Drug	Dose
Rifampicin	600 mg PO BD × 2 days
Ciprofloxacin(Avoid in Pregnancy)	500 mg PO single dose
Ceftriaxone	250 mg IM single dose

Vaccines recommended for contacts:

Meningococcal vaccine (ACWY ± B)
Hib vaccine (if not immunized)