Central nervous system infections

Question 1

List the main routes of infection to the CNS

Answer 1

Most common- blood borne
Direct spread through cribriform plate
Parameningeal suppuration from otitis media/sinusitis
Direct spread through dura defects- trauma/surgery

Question 2

Describe the clinical features of bacterial meningitis and list common causative organisms

Answer 2

Endotoxins of G-ve na lipotechoic peptidoglycan components of G+ve bac cell walls are potent inflam mediators
TNF, IL1, 6 and 8, PAF, NO etc
Neutrophils migrate to CSF
Release proteolytic products, toxic O radicals, CSF pressure increases due to cap inflam and infiltration
Damage to vascular epi- alters permeability of the BBB

Symptoms- meningism- headache global, neck, back stiffness, Kernig’s sign, nausea, vom, photophobia
Fever- not always seen
Rash- petechial- meningococcal but also streptococcal, Hib sepsis and enteroviral infection

Impaired consciousness/seizures
In infants- typical signs absent- convulsions, flaccid, bulging fontanelle, fever and vom, strange cry

Causes:
Neisseria Meningiditis- infants
S. pneuominae- young kids/elderly
Hib- uncommon with vaccine
Group B strep and e coli- neonates (babies)
Listeria monocytogenes- neonates/immunocompromised

Question 3

Describe the investigation of suspected bacterial meningitis

Answer 3

Lumbar puncture- rapid test bac/virus- risk of herniation/bleeding
CT first due to risk of herniation
Gram stain- inaccurate
PCR
Agglutination tests

Question 4

List the main causes of viral meningitis

Answer 4

HIV
Flavivirus
Mumps
Herpes
Enteroviruses

Question 5

Outline clinical features of encephalitis- inflammation of brain

Answer 5

Cerebral dysfunction

Inability, ataxia, excessive reflex

Question 6

List the most important organisms causing encephalitis

Answer 6

Herpes simplex
Enterovirus
Listeria
Measles
Mumps
Mycobacterium  tuberculosis
Chicken pox, measles

Question 7

List the clinical features of myelitis

Answer 7

Inflammation of spinal cord (w or without encephalitis)
Transverse- acute transection of cord- vasculitis
VZV, TB, syphilis
MMR, URTIs
Direct invasion of cord- VZV, HTLV-1
Ascending- flaccid, paralysis, sensory loss
Ant horn cells- muscle pain, no sensory, bladder dysfunction

Question 8

Discuss the concept of encephalomyelitis and common causes

Answer 8

Overlap in presentation and causation
Entry- CNS
- Respiratory 
- GI tract
- Subcutaneous
- Mucosa
peripheral nerve- polio, rabies
viruses- HIV, MM, polio, West nile
Arboviruses