Week 6 infections

Introduction to CNS Infections – Study Guide

1. Overview of CNS Infections
CNS (Central Nervous System) infections affect the brain and spinal cord, often
involving serious complications. They can be caused by bacteria, viruses, fungi,
or parasites and typically require urgent medical intervention.

Types of CNS Infections

Type Definition
Meningitis Inflammation of the meninges
(protective layers around the brain
& spinal cord).
Encephalitis Inflammation of the brain
parenchyma.
Brain Abscess Localized pus collection within the
brain tissue.
Myelitis Inflammation of the spinal cord.
2. Pathogenesis of CNS Infections
Routes of Infection
Route Description
Hematogenous Spread Pathogens enter through the
bloodstream and cross the blood-
brain barrier (BBB).
Direct Extension Infection spreads from adjacent
structures (e.g., sinuses, middle
ear).
Peripheral Nerve Spread Viruses like rabies travel along
peripheral nerves to the CNS.
Penetrating Trauma/Surgery Direct inoculation of pathogens
into the CNS.
Host Defense Mechanisms
• Blood-Brain Barrier (BBB) – Limits pathogen entry but also restricts
immune response.
• Microglia & Astrocytes – Play roles in immune defense.
• Cytokines & Immune Cells – Contribute to neuroinflammation but may
also cause damage.
3. Bacterial Meningitis
Common Pathogens
Age Group Causative Organisms
Neonates • Escherichia coli
• Group B Streptococcus
• Listeria monocytogenes
Children • Streptococcus pneumoniae
• Neisseria meningitidis
• Haemophilus influenzae B
Adults • Streptococcus pneumoniae
• Neisseria meningitidis
Elderly / Immunocompromised • Listeria monocytogenes
• Gram-negative bacilli
Clinical Features
• Classic Triad: Fever, headache, neck stiffness.
• Other Symptoms: Photophobia, nausea, vomiting, altered mental status,
seizures.
• Meningococcal Meningitis: May present with petechial rash.
Diagnosis
Diagnostic Test Findings
Lumbar Puncture (CSF Analysis) ↓ Glucose, ↑ Protein, ↑ WBCs
(neutrophils)
Blood Cultures Identify causative bacteria.
Imaging (CT/MRI) Used if there is a risk of brain
herniation before LP.
Treatment
Age Group Empirical Antibiotic Therapy
Neonates Ampicillin +Cefotaxime/Gentamicin
Children & Adults Ceftriaxone + Vancomycin
Elderly / Immunocompromised Ceftriaxone + Vancomycin +
Ampicillin (Listeria coverage)
Adjunct Therapy:
• Dexamethasone (reduces inflammation in S. pneumoniae infections).
• Supportive care: IV fluids, seizure management, oxygen therapy.

4. Viral Meningitis & Encephalitis

Common Pathogens
 Pathogen Type Examples
Enteroviruses • Coxsackievirus
• Echovirus
Herpesviruses • HSV-1 (temporal lobe
encephalitis)
• VZV
• CMV
Arboviruses • West Nile Virus,
• Japanese Encephalitis
Clinical Features
• Viral Meningitis: Milder than bacterial, presents with headache, fever,
photophobia.
• Encephalitis: Includes altered mental status, seizures, focal neurological
deficits.
Diagnosis
Diagnostic Test Findings
CSF Analysis • Lymphocytic pleocytosis,
• normal/mild ↑ protein,
• normal glucose
PCR for Viruses Detects HSV, VZV, Enteroviruses
MRI Temporal lobe involvement in HSV
encephalitis
Treatment
Virus Treatment
HSV, VZV Acyclovir
CMV Ganciclovir / Foscarnet
Others Supportive care (fluids, seizure
control, fever management)
5. Brain Abscess
Common Pathogens
Source Organisms
Polymicrobial • Streptococcus, Bacteroides
• Staphylococcus aureus
Otogenic/Sinus-related • S. pneumoniae
• anaerobes
Post-Trauma/Surgery • Staphylococcus aureus
• Pseudomonas
Clinical Features
• Fever, headache, focal neurological deficits.
• Increased ICP: Vomiting, papilledema, altered consciousness.
• Seizures in some cases.
Diagnosis
Diagnostic Test Findings
CT/MRI with Contrast Ring-enhancing lesion
Aspiration/Biopsy Identifies causative organism
Treatment
Therapy Approach
Empirical Antibiotics Ceftriaxone + Metronidazole ±
Vancomycin
Surgical Drainage If abscess >2.5 cm or mass effect
present
6. Spinal Cord Infections (Myelitis)
Causes & Pathogens
Type Examples
Viral • Poliovirus
• Enteroviruses
• West Nile Virus
Bacterial • Mycobacterium tuberculosis
(Pott’s disease)
Parasitic • Schistosoma
• Toxoplasma
Clinical Features
• Motor & Sensory Deficits: Weakness, paralysis in severe cases.
• Bowel/Bladder Dysfunction: Possible in spinal cord involvement.
Diagnosis & Treatment
Test Finding
MRI Spine (Contrast) Identifies inflammation & lesions
CSF Analysis Confirms infectious cause
Treatment Supportive care for viral cases,
antimicrobial therapy as needed
7. Prevention of CNS Infections
Vaccination
Vaccine Protects Against
Meningococcal Vaccine Neisseria meningitidis
Pneumococcal Vaccine Streptococcus pneumoniae
Hib Vaccine Haemophilus influenzae type B
Rabies Vaccine Rabies virus
Prophylactic Antibiotics
• For Close Contacts of Meningococcal Meningitis: Rifampin,
Ciprofloxacin, or Ceftriaxone.
Hygiene & Public Health Measures
• Hand hygiene, mosquito control (for arboviruses), food safety measures.
Meningitis – Study Guide
1. Overview of Meningitis
Meningitis is the inflammation of the meninges, the protective membranes
surrounding the brain and spinal cord. It is a medical emergency requiring rapid
diagnosis and treatment.
Types of Meningitis
Type Cause
Bacterial Meningitis Caused by pyogenic bacteria.
Medical emergency.
Viral Meningitis Most common type; self-limited.
Fungal Meningitis Seen in immunocompromised
patients.
Parasitic Meningitis Rare; associated with exposure to
freshwater sources (e.g., Naegleria
fowleri).
Aseptic Meningitis Non-infectious causes (e.g.,
autoimmune, drug-induced,
malignancy).
2. Clinical Features of Meningitis
Classic Triad
1. Fever
2. Headache (90% of patients)
3. Neck Stiffness (Meningismus)
Other Symptoms
• Altered Mental Status (Confusion ⟷ Lethargy ⟷ Coma)
• Nausea/Vomiting
• Photophobia & Phonophobia
• Seizures
Signs of Meningeal Irritation
 Sign Description
Nuchal Rigidity Stiff neck due to meningeal
inflammation.
Brudzinski’s Sign Passive neck flexion leads to
involuntary hip/knee flexion.
Kernig’s Sign Pain on knee extension when the
hip is flexed.
Signs of Increased Intracranial Pressure (ICP)
• Papilledema (optic disc swelling)
• Abducens (6th CN) palsy
• Cushing’s Reflex (hypertension, bradycardia, irregular respiration)

3. Acute vs. Chronic Meningitis

Type Etiology Clinical Course
Acute Meningitis Bacterial, Viral Rapid onset (<24 hrs),
requires urgent
treatment
Chronic Meningitis Bacterial Symptoms persist >4
(Mycobacterium weeks
tuberculosis), Fungal
(Cryptococcus
neoformans), Parasitic
(Schistosoma)
4. Diagnosis of Meningitis
Stepwise Approach
1. Clinical History & Exam
• Consider risk factors: recent infections, travel, immunosuppression.
2. Laboratory Tests
• CBC, CMP, Blood Cultures, PT/PTT.
3. Imaging (If Needed Before LP)
• CT/MRI Brain if:
• Focal neurologic deficit
• New-onset seizure
• Papilledema
• Altered consciousness
• Immunocompromised status
4. Lumbar Puncture (LP) & CSF Analysis
Cerebrospinal Fluid (CSF) Analysis in Meningitis
 Parameter Bacterial Viral Fungal Tuberculou
s
Opening ↑ High Slightly ↑ Normal/↑ Usually ↑
Pressure
WBC Count > 200/mm³ < 200/mm³ < 50/mm³ 20-30/mm³
Differential PMNs Monocytes Monocytes Monocytes
Glucose ↓ Low Normal ↓ Low ↓ Low
Protein ↑ Very High Normal/↑ ↑ High ↑ High
5. Bacterial Meningitis
Common Pathogens by Age Group
Age Group Pathogens Empiric Treatment
Neonates (<1 mo) • Group B Ampicillin +
Streptococcus, Gentamicin/Cefotaxime
• E. coli,
• Listeria
monocytogenes
1-23 months • S. pneumoniae, Ceftriaxone + Vancomycin
• N. meningitidis,
• H. influenzae
2-18 years • N. meningitidis Ceftriaxone + Vancomycin +
• S. pneumoniae Ampicillin

19-59 years • S. pneumoniae Ceftriaxone + Vancomycin

• N. meningitidis
>60 years • S. pneumoniae Ceftriaxone + Vancomycin +
Listeria Ampicillin
• monocytogenes
Treatment
• Empirical Antibiotics – Should be administered immediately after
lumbar puncture.
• Adjunct Therapy:
• Dexamethasone (reduces inflammation, hearing loss in S. pneumoniae,
H. influenzae).
• Supportive care: IV fluids, seizure management, oxygen therapy.

6. Viral Meningitis
Common Viral Causes
Type Examples
Enteroviruses • Coxsackievirus,
• Echovirus,
• Poliovirus
Arboviruses • West Nile Virus
• Japanese Encephalitis
Herpesviruses HSV-1 (encephalitis), VZV, CMV
Other HIV, Mumps (unvaccinated
individuals)
Diagnosis & Treatment
Test Finding
CSF Analysis Lymphocytic pleocytosis, normal
glucose
PCR for Viruses Detects HSV, VZV, Enteroviruses
Treatment Supportive (fluids, analgesia)
HSV/VZV Meningitis Acyclovir
CMV Meningitis Ganciclovir/Foscarnet
7. Case Study
Patient Presentation
• 76-year-old woman with diabetes and hypertension
• 12-day history of headache and confusion
• Previously diagnosed with left middle ear infection, started on antibiotics
• Progressive decline over 2 days, fever (38.8°C)
Physical Examination
• Requires stimulation to awaken, altered mental status
• Neck stiffness, worsening pain on flexion/extension
• No rash, no focal neurologic deficits
Laboratory Findings
• Leukocytosis (21,000 WBCs/mm³)
• CSF Findings:
• WBC Count: 5,115 cells/mm³ (95% PMNs)
• Protein: 436 mg/dL
• Glucose: 108 mg/dL (serum glucose: 185 mg/dL)
Diagnosis
Bacterial Meningitis
• CSF analysis favors bacterial etiology:
• Markedly elevated WBC count
• PMN predominance
• Low glucose
• Very high protein
Management
1. Empirical IV Antibiotics: Ceftriaxone + Vancomycin + Ampicillin
2. Dexamethasone to reduce inflammation
3. Supportive Care: IV fluids, seizure management

8. Prevention of Meningitis
Vaccination
Vaccine Pathogen Covered
Meningococcal Vaccine Neisseria meningitidis
Pneumococcal Vaccine Streptococcus pneumoniae
Hib Vaccine Haemophilus influenzae type B
Rabies Vaccine Rabies virus
Prophylaxis
• Close Contacts of Meningococcal Meningitis: Rifampin, Ciprofloxacin,
or Ceftriaxone.
• Hygiene & Public Health Measures: Hand hygiene, mosquito control,
safe food handling.

Encephalitis – Study Guide

1. Overview of Encephalitis
Encephalitis is the diffuse inflammation of the brain parenchyma, often
associated with meningitis (meningoencephalitis). It is commonly caused by viral
infections and presents with a global neurological deficit rather than
meningeal signs.
Etiology: Common Causes
Cause Examples
Herpesviruses • HSV-1 (most common,
severe),
• HSV-2 (neonates),
• VZV,
• EBV,
• CMV
Arboviruses West Nile Virus, St. Louis
Encephalitis, Eastern & Western
Equine Encephalitis
Post-Infectious Causes Acute Disseminated
Encephalomyelitis (ADEM), Acute
Hemorrhagic Leukoencephalitis
Others Rabies, Measles (Subacute
Sclerosing Panencephalitis)
2. Clinical Features of Encephalitis
Unlike meningitis, encephalitis presents with altered mental status, seizures,
and cortical dysfunction rather than meningismus.
Early Symptoms (Viral Prodrome)
• Fever, malaise, myalgia
• Headache
Neurological Features
Category Symptoms
Global Neurological Deficits Drowsiness, fatigue, seizures,
memory impairment, personality
changes, hallucinations
Focal Neurological Deficits Hemiparesis, aphasia, cranial
nerve deficits, movement disorders
Seizures Present in 30-60% of cases, often
focal in onset
3. Case Study: 61-Year-Old Man with Encephalitis
Patient Presentation
• 61-year-old man with no past medical history
• 2-week history of mild headaches → worsening over the past 5 days
• Behavioral changes, excessive sleepiness
• Seizure episode:
• Left head turn → eye deviation
• Left hand → arm → generalized tonic-clonic activity
• No neck stiffness or meningismus
Physical Examination
• No meningeal signs
• No rash
• No focal neurological deficits
Laboratory & CSF Analysis
Test Finding
CBC, CMP Normal except for mildly elevated
liver enzymes
CSF WBC Count 5,146 cells/mm³ (97%
mononuclear)
CSF Protein 77 mg/dL (mildly elevated)
CSF Glucose 91 mg/dL (normal, systemic
glucose: 140 mg/dL)
Imaging
• MRI Brain:
• Diffusion-weighted imaging (DWI)
• Fluid-attenuated inversion recovery (FLAIR)
• T2-weighted imaging
Diagnosis
• Most likely viral encephalitis (Herpes Simplex Encephalitis suspected).
• No meningeal signs → rules out meningitis.
• No focal neurological deficits → rules out focal cerebritis or brain
abscess.

4. Herpes Simplex Encephalitis (HSE)

HSV-1 is the most common cause of sporadic viral encephalitis.
• Classic Presentation:
• Headache, fever, malaise
• Memory impairment & hallucinations
• Severe cases: Rapid progression to coma and death in 2 weeks.
MRI Findings
• Temporal lobe involvement (key feature)
• Edema, hemorrhage, necrosis
Diagnosis
• CSF PCR for HSV (gold standard)
• MRI: Hyperintensities in temporal lobe on T2/FLAIR imaging.
Treatment
• IV Acyclovir (ASAP – reduces mortality significantly).
5. Other Viral Encephalitis Causes & Features
Pathogen Features Key Findings
Varicella-Zoster Virus Reactivation from Vasculitis, infarcts,
(VZV) sensory ganglia, MRI: multifocal lesions
affects vascular
endothelium
West Nile Virus (WNV) <1% develop Acute flaccid
neuroinvasive disease paralysis,
chorioretinitis
Post-Infectious Demyelination post- MRI: diffuse white
(ADEM) viral infection matter hyperintensities
6. Diagnosis of Encephalitis
Stepwise Approach
1. Clinical History & Exam
• Viral prodrome, behavioral changes, seizures.
2. Laboratory Tests
• CBC, CMP, Blood cultures, Viral PCR (HSV, VZV, CMV, EBV).
3. CSF Analysis
• Lymphocytic pleocytosis (high WBCs, mostly mononuclear).
• Normal or mildly elevated protein.
• Normal glucose (except in HSV or TB).
4. Imaging
• MRI (FLAIR/T2) – temporal lobe hyperintensities in HSV.
CSF Findings in Viral Encephalitis
Parameter Finding
Opening Pressure Normal/slightly elevated
WBC Count 50-500 cells/mm³ (mononuclear)
Protein Mildly elevated
Glucose Normal (except in HSV/TB)
7. Treatment of Viral Encephalitis
Cause Treatment
HSV/VZV IV Acyclovir
CMV IV Ganciclovir/Foscarnet
West Nile Virus Supportive Care
Post-Infectious (ADEM) Steroids (reduces inflammation)
Supportive Care
• Seizure Management: Antiepileptics if needed.
• Fever Control & IV Fluids
• Respiratory Support in Severe Cases

8. Prevention of Encephalitis
Pathogen Preventive Measures
HSV Early recognition & treatment with
IV Acyclovir
VZV Varicella Vaccine, post-exposure
prophylaxis
West Nile Virus Mosquito control, avoid stagnant
water
Rabies Post-exposure prophylaxis (PEP)
with vaccine & immunoglobulin

Cerebritis & Brain Abscess – Study Guide

1. Overview of Cerebritis & Brain Abscess

Cerebritis is an early stage of a brain abscess, where the brain parenchyma
becomes inflamed due to an infection. If untreated, it progresses to a brain
abscess, which is a focal, suppurative infection surrounded by a vascular
capsule.
Epidemiology
• Uncommon: Incidence ~1 per 100,000 people per year.
• Mortality Rate: ~10-20%, despite treatment.
Pathophysiology
1. Cerebritis (early stage): Diffuse inflammation of the brain parenchyma.
2. Encapsulation (late stage): Formation of a ring-enhancing abscess with
surrounding edema.

2. Etiology & Pathogenesis

Routes of Infection
Route Description
Direct Extension From adjacent infections (otitis,
mastoiditis, sinusitis, dental
abscess).
Hematogenous Spread Through bloodstream (e.g., from
infective endocarditis, lung
abscess).
Post-Surgical/Trauma After neurosurgical procedures or
penetrating head trauma.
Cryptogenic No identifiable source (~15% of
cases).
Common Pathogens
Infection Source Likely Pathogens
Otitis/Mastoiditis (33%) Streptococcus, Bacteroides,
Pseudomonas
Sinusitis Streptococcus, Staphylococcus
aureus, Haemophilus influenzae
Hematogenous Spread (25%) Streptococcus, Staphylococcus
aureus
Post-Surgical Staphylococcus aureus,
Pseudomonas
3. Clinical Features of Cerebritis & Brain Abscess
Classic Triad (Present in <50% Cases)
1. Headache (most common symptom, 75%).
2. Fever (variable, may be absent).
3. Focal Neurological Deficit (60% cases).
Other Symptoms
Symptom Frequency
Seizures 15-35%
Aphasia, Hemiparesis, Visual Variable
Field Cuts
Altered Mental Status Severe cases
Signs of Increased ICP Vomiting, papilledema,
bradycardia
4. Case Study: 56-Year-Old Man with Cerebritis
Patient Presentation
• 56-year-old man with diabetes mellitus, no regular medical care.
• 1-week history of progressively worsening headache and aphasia.
• Intermittent fevers and severe dental pain (suspected periapical
abscess).
Physical Examination
• Expressive Aphasia:
• Impaired fluency
• Intact comprehension & repetition
• Otherwise unremarkable neurological exam.
Imaging Findings (MRI Brain)
• Enhancing lesion in the left frontal lobe.
• Surrounding vasogenic edema (suggestive of an abscess).
Diagnosis
• Focal neurological deficit (aphasia) + ring-enhancing lesion on MRI =
Brain Abscess.
• Potential Source: Dental abscess (hematogenous spread).

5. Diagnosis of Cerebritis & Brain Abscess

Stepwise Approach
1. Clinical History & Exam
• Look for infection source (sinusitis, otitis, dental abscess, endocarditis).
2. Laboratory Tests
• CBC (leukocytosis), CMP, Blood Cultures.
3. Imaging Studies
• MRI Brain (gold standard):
• T1-weighted with contrast: Ring-enhancing lesion.
• T2-weighted: Vasogenic edema.
• Diffusion-weighted imaging (DWI): Differentiates abscess from necrotic
tumors.
4. Definitive Diagnosis
• Aspiration & Culture (if needed).
MRI Findings in Brain Abscess
Imaging Type Findings
T1 + Contrast Ring-enhancing lesion
T2-weighted Surrounding edema
DWI (Diffusion-Weighted Imaging) Restricted diffusion (confirms
abscess)
6. Treatment of Cerebritis & Brain Abscess
Empirical Antibiotic Therapy
Condition Empirical Treatment
Otogenic/Sinus-related Abscess Ceftriaxone + Metronidazole + Vancomycin
Post-Surgical Abscess Ceftriaxone + Vancomycin
Hematogenous Spread Ampicillin/Sulbactam + Ceftriaxone +
Metronidazole
• Duration: 4-6 weeks IV antibiotics.
Surgical Intervention
Indication for Surgery Procedure
Abscess >2.5 cm Surgical drainage or aspiration
Loculated Abscess Stereotactic aspiration
Gas formation (Anaerobic Surgical excision
infection)
Posterior Fossa Abscess Urgent drainage
(Brainstem compression risk)
Adjunctive Therapy
• Seizure Prophylaxis (if seizures occur).
• Dexamethasone (only if significant edema & mass effect).
• IV Fluids, Fever Management, ICU Support if needed.

7. Prognosis & Complications

Complication Risk
Seizures 30-50%
Hydrocephalus Due to obstruction of CSF flow
Herniation Risk if abscess is large & causing
mass effect
Residual Neurologic Deficit 20-30% of patients
• Mortality: 10-20% despite treatment.
• Better Prognosis if diagnosed early and treated aggressively.

8. Prevention of Cerebritis & Brain Abscess

Preventing Primary Infections
Condition Prevention Strategy
Otitis & Mastoiditis Early antibiotic treatment
Sinusitis Prompt drainage of purulent
infections
Dental Infections Timely dental care & treatment
of abscesses
Endocarditis Prophylactic antibiotics in high-
risk patients
Prophylactic Antibiotics
• For post-neurosurgical patients to prevent iatrogenic abscesses.
• Immunocompromised patients should receive prophylaxis against
opportunistic infections.