Neuroscience-III Module — Final Year MBBS

AIM LEARNING CYCLE | STUDENT SUPPORT

FINAL YEAR MBBS | KMU CURRICULUM | NEUROSCIENCE-III

Student Memory Support

Topic 7. CNS Infections: Meningitis & Encephalitis

High-yield clinical recall, diagnostic distinctions, pharmacology, complications and KMU examination reinforcement.

1. High-Yield Flashcards

Tap each question to reveal the answer.

Which anatomical structures are primarily inflamed in meningitis?

The leptomeninges (pia and arachnoid mater) and the subarachnoid space.

What is the characteristic CSF pattern in acute bacterial meningitis?

Neutrophilic pleocytosis, markedly increased protein and reduced CSF glucose.

What CSF findings usually favor uncomplicated viral meningitis?

Predominantly lymphocytic cells, mildly increased protein and normal glucose.

What clinical and CSF pattern suggests tuberculous meningitis?

Subacute fever and headache with lymphocytic CSF, high protein and low glucose.

Which organisms are important causes of acute bacterial meningitis in adults?

Streptococcus pneumoniae and Neisseria meningitidis are major causes.

What does Kernig sign indicate?

Pain or resistance during knee extension with the hip flexed suggests meningeal irritation.

What is a positive Brudzinski sign?

Involuntary hip and knee flexion during passive neck flexion, suggesting meningeal irritation.

Which findings require special assessment before lumbar puncture?

Focal neurological deficits, markedly impaired consciousness, signs of brain shift, shock or significant bleeding risk.

What is the immediate antimicrobial principle in suspected bacterial meningitis?

Start appropriate empirical intravenous antibiotics promptly without waiting for delayed lumbar puncture or culture results.

Why are basal meningeal exudates important in tuberculous meningitis?

They may obstruct CSF circulation, involve cranial nerves and cause vasculitic cerebral infarction.

Which brain region is characteristically involved in HSV encephalitis?

The temporal lobes, particularly medial temporal structures.

Which investigation helps confirm herpes simplex encephalitis?

HSV PCR testing of CSF, supported by clinical and MRI findings.

What is the first-line antiviral treatment for suspected HSV encephalitis?

Intravenous acyclovir, which inhibits viral DNA replication.

Which features may indicate meningitis in a young infant?

Fever, poor feeding, irritability, lethargy, vomiting or a bulging fontanelle; neck stiffness may be absent.

Which long-term complications require monitoring after childhood bacterial meningitis?

Sensorineural hearing loss, cognitive impairment, learning difficulties and neurodevelopmental problems.

2. Mnemonics

Mnemonic 1 — Classical Meningitis Presentation

FHN

F — Fever
H — Headache
N — Neck stiffness

The classical triad is important but may be incomplete, particularly in infants.

Mnemonic 2 — Initial Anti-Tuberculosis Drugs

HRZE

H — Isoniazid
R — Rifampicin
Z — Pyrazinamide
E — Ethambutol

These drugs form the standard initial multidrug treatment combination for tuberculosis.

Mnemonic 3 — Serious CNS Infection Complications

SHIH

S — Seizures
H — Hydrocephalus
I — Infarction
H — Hearing loss

Complications differ by organism, age and disease severity.

3. Memory Tables

Table 1 — CSF Findings in Common Meningitis Types

Finding	Bacterial	Viral	Tuberculous
Onset	Acute	Usually acute	Usually subacute
Predominant cells	Neutrophils	Lymphocytes	Lymphocytes
Protein	Markedly raised	Mildly raised	Raised, often markedly
Glucose	Reduced	Usually normal	Reduced
Useful microbiology	Gram stain, culture, PCR	Viral PCR	TB molecular testing, culture

These are typical patterns rather than absolute rules. Early disease and prior antimicrobial treatment can alter CSF findings.

Table 2 — Meningitis Versus Encephalitis

Feature	Meningitis	Encephalitis
Main site	Meninges	Brain parenchyma
Prominent symptoms	Headache, fever, neck stiffness	Confusion, behavior change, seizures
Brain dysfunction	Variable; may occur in severe disease	Prominent
Investigation focus	CSF analysis and microbiology	CSF PCR, MRI and EEG when indicated

4. Rapid Revision Points — Last-Minute Revision

Must Remember

Bacterial meningitis typically causes neutrophilic CSF with low glucose and high protein.
Viral meningitis usually causes lymphocytic CSF with preserved glucose.
Subacute meningitis with low CSF glucose suggests tuberculosis.
Basal exudates in TB meningitis may cause hydrocephalus and vasculitic infarction.
Meningeal signs can be absent in infants despite serious CNS infection.
Suspected bacterial meningitis requires prompt empirical intravenous antibiotics.
Consider lumbar puncture contraindications before obtaining CSF.
HSV encephalitis is associated with temporal lobe dysfunction and focal seizures.
Acyclovir inhibits viral DNA polymerase and requires renal safety monitoring.
Childhood bacterial meningitis may cause persistent hearing and learning impairment.

5. Clinical Memory Hooks

Acute fever + meningism + neutrophilic CSF + low glucose → Acute bacterial meningitis; urgent intravenous antibiotics.

Weeks of headache + cranial nerve palsy + basal meningeal enhancement → Suspect tuberculous meningitis with basal inflammatory exudates.

Fever + personality change + focal seizures + temporal MRI abnormalities → Suspect HSV encephalitis; initiate intravenous acyclovir.

Infant with fever + poor feeding + lethargy without neck stiffness → Meningitis remains possible and requires urgent assessment.

6. Starred High-Yield Exam Points

⭐ CSF distinction: Neutrophils + low glucose + markedly high protein favor bacterial meningitis.
⭐ TB meningitis: Basal exudates can cause hydrocephalus, cranial neuropathy and vasculitic stroke.
⭐ Diagnostic safety: Never delay urgent antimicrobial treatment simply to obtain CT imaging or perform lumbar puncture.
⭐ HSV encephalitis: CSF HSV PCR is the preferred etiological test; temporal lobe abnormalities are an important imaging clue.
⭐ Drug of choice: Intravenous acyclovir is initiated promptly in suspected HSV encephalitis.
⭐ Anti-TB adverse effect: Ethambutol may cause optic neuropathy; isoniazid may cause peripheral neuropathy.
⭐ Pediatric sequelae: Sensorineural hearing loss and neurodevelopmental difficulties require follow-up after bacterial meningitis.