2.1 CNS Infective Diseases

Question 1

Which demographic is most at risk of meningitis?

Answer 1

Children under 5

Question 2

What is the most common cause of meningitis?

Answer 2

Infection (bacterial, viral, fungal, parasitic etc.)

Question 3

How can pathogens gain access to the subarachnoid space?

Answer 3

Direct (anatomical defect, otitis media, sinusitis), or indirect (haematogenous spread, adjacent infected areas)

In terms of blood, this often occurs through BSCFB; more permeable than BBB

Question 4

What are the most common bacteria that cause meningitis?

Answer 4

• Pneumococcus (AKA strep. pneumoniae)
• Meningococcus (AKA neisseria meningitidis)

Question 5

How can bacterial meningitis be spread? Why is this important?

Answer 5

Coughing, sneezing, or direct contact (need to notify close contacts)

Question 6

Describe the pathophysiology of bacterial meningitis

Answer 6

• Bacteria enters bloodstream and replicates
• Bacteria crosses the blood brain barrier, and enters into CSF
• They undergo lysis, leading to release of inflammatory mediators and immune cell recruitment
• Increased BBB permeability
• Cerebral oedema, increasing ICP (secondary to albumin leaking in, creating osmotic gradient)
• Can lead to thrombophlebitis > infarction
• Adhesions form between meninges (impinging cranial nerves and causing hydrocephalus)

Question 7

What is thrombophlebitis?

Answer 7

Blood vessel blocked by thrombus formed due to vascular inflammation

Question 8

What are the classic clinical features of meningitis?

Answer 8

• Fever
• Nuchal rigidity
• Altered mental state
• Headache
• Nausea and vomiting (raised ICP)

Question 9

What are three signs that may show up in meningitis?

Answer 9

• Nuchal rigidity
• Kernig’s sign (pain on straightening leg when lying flat)
• Brudzinski’s sign (flexion of neck causes flexion of knee)

Question 10

What is a unique feature of menigococcal meningitis?

Answer 10

• Petechial/ecchymoses rash
• Will not dissappear when pressed

Question 11

Define encephalitis, macro/microscopically

Answer 11

Macro: dffuse inflammation of the brain parenchyma
Micro: neuronal death, necrosis, astrocytosis

Question 12

Encephalopathy vs encephalitis

Answer 12

-opathy: Dysfunction without inflammation
-itis: Dysfunction with inflammation

Question 13

What is the most common causative organism of encephalitis?

Answer 13

Herpes Simplex Virus (2° to HSV; only 25% of patients have history of cold sores)

Think of Brian from Family Guy, when he gets herpes; he does strange things, maybe he has altered mental status 2° to encephalitis…

Question 14

Investigations for encephalitis

Answer 14

• Immunohistochemistry
• Electron microscopy

Question 15

What are arboviruses? What are some of the more common arboviruses that can cause encephalitis?

Answer 15

• Viruses that are transmitted by vectors such as mosquitos
• Common ones include Ross River Virus and Murray River Encephalitis Virus

Question 16

Common organism in bacterial encephalitis

Answer 16

Mycobacterium tuberculosis

Question 17

Common cause of parasitic encephalitis

Answer 17

Cerebral malaria

Question 18

Common cause of fungal encephalitis

Answer 18

Cryptococcal infection

Question 19

What is the common mechanism of para/post-infectious encephalitis?

Answer 19

Autoimmune/inflammatory

Question 20

What are the time courses of the different kinds of encephalitis?

Answer 20

Bacterial/viral: Acute
Parasitic/fungal: More insidious

Question 21

Investigations for meningitis

Answer 21

• Physical exam
• Blood test
• Lumbar puncture (if no raised ICP)
• CT scan

Question 22

Presenting features of encephalitis

Answer 22

• Altered mental status
• Psychosis/agitation
• Raised ICP (headache, nausea, vomiting)
• Fever
• Seizures

Question 23

The lasting complications of encephalitis depend on…

Answer 23

Regions of brain area affected

Question 24

What is a cerebral abscess?

Answer 24

Focal area of suppural infection in the brain parenchyma

Question 25

Describe cerebral abscess

Answer 25

- Liquefactive necrosis - Inflammatory mediators > oedema and neutrophils - Pus forms due to dead neutrophils in necrotic core - Demarcated by granulation tissue

Question 26

Outline the pathophysiology of cerebral abscess

Answer 26

- Pathogen is detected within the brain environment - Microglia and astrocytes are recruited, and release inflammatory mediators - Mediators enable neutrophils, macrophages, and lymphocytes to enter site of infection, broadening area of inflammation - Vascularised granulation tissue walls of infection, but much tissue undergoes necrosis regardless

Question 27

Common causative organisms of cerebral abscess

Answer 27

- Staph auerus - Norcardia/toxoplasma

Question 28

What are some conditions that predispose to developing a cerebral abscess?

Answer 28

- Surgery - Nearby infections (e.g. mastoiditis) - Haematogenous spread - Other conditions (e.g. endocarditis)

Question 29

True or false: most patients with cerebral abscess experience fever, headache, and focal neurological defecits

Answer 29

- False - This is seen in <20% of patients

Question 30

Complications of cerebral abscess

Answer 30

- Focal loss of neurons - Raised ICP (vasogenic oedema); can cause herniation - If ruptured: meningitis, ventriculitis

Question 31

Where does infective meningitis most commonly spread from?

Answer 31

Nasopharyngeal colonisation

Question 32

Meningitis is defined the presence of an abnormal number of ____ in CSF

Answer 32

White blood cells

Question 33

What is the most common causative organism of community acquired viral meningitis?

Answer 33

Enterovirus

Question 34

What are the early investigations in a suspected meningitis case?

Answer 34

- CT head - Lumbar puncture

Question 35

What blood tests should be ordered if you suspect CNS infection?

Answer 35

- EUC/LFT (alternative cause of drowsiness) - CBE (Neutrophils: bacterial; lymphocytes: viral etc.) - Coags (low platelets contraindicate LP)

Question 36

True or false: you should not give antibiotics for a suspected CNS infection until imaging results have returned

Answer 36

False. This is associated with higher mortality. Do it ASAP.

Question 37

When might PCR be useful in identifying the causative organism for CNS infection?

Answer 37

When the patient is already on antibiotics