CNS Infections

Question 1

How can chickenpox cause stroke?

Answer 1

Varicella virus reactivated in adulthood causes shingles
Infection of the blood vessels of the brain can cause restriction and clotting
This can later cause stroke

Question 2

How can a microbe affect CNS function?

Answer 2

Immune mediate CNS damage
-Acute disseminated encephalomyelitis (autoimmune attack)
-Infection triggered antibody associated (post viral encephalitis)
-Immune reconstitution inflammatory syndrome (HIV medication)

Infection triggered metabolic catastrophes
-Reye’s syndrome
-Acute necrotising encephalopathy

Toxin mediated diseases
-Tetanus

Systemic sepsis
-Septic encephalopathy

Question 3

What factors affect neurovirulence?

Answer 3

Infectious dose
Host immune system
Neurovirulent features of the organism

Question 4

How do CNS infections cause brain damage?

Answer 4

Inflammation
-BBB breakdown
-Cytokine release
-Endarteritis and thrombosis
Raised ICP
Direct neuronal injury

Question 5

What are Koch’s postulates?

Answer 5

Microbe must be present in every case

Microbe must be isolated fr the diseased host and grown in pure culture

The disease must be reproduced when a pure culture is introduced to a susceptible host

The microbe must be recoverable from the experimentally infected host

Question 6

What are the issues with Koch’s postulates?

Answer 6

Might not have an animal model for that disease (human only)
Not every pathogen can be grown in more culture

Question 7

How is the likelihood of a pathogen being the causative agent evaluated?

Answer 7

Immune response in blood or CSF

Question 8

What types of neuro infection are there?

Answer 8

Meningitis (enterovirus, mumps)
Ventriculitis (CMV)
Encephalitis (HSV-1)
Myelitis (poliomyelitis)
Radiculitis, ganglionitis (shingles, Bell’s palsy)

Question 9

What kind of tests can you do on CSF?

Answer 9

Cell count and cytology
Gram stain
Antigen detection
Microbial culture (meningitis)
CSF:plasma glucose or lactate (drop indicates bacterial infection)
PCR (viral)
Antibody tests

Question 10

What are the cardinal symptoms of encephalitis?

Answer 10

Fever
Alteration in consciousness level
Seizures

Question 11

How might the neurological/neuropsychiatric symptoms help elucidate aetiology?

Answer 11

Some pathogens have focal preferences
eg HSV and limbic encephalitis

Question 12

What viruses would be investigated for an immunocompetent patient presenting with encephalitis in the UK

Answer 12

HSV
VZV (chickenpox)
Enteroviruses

Question 13

Which imaging technique is better at picking up early herpes encephalitis?

Answer 13

MRI

Question 14

What causes periodic lateralised epileptiform discharges on EEG?

Answer 14

Any severe damage to the temporal lobe

Question 15

What is the gold standard for diagnosis of herpes encephalitis?

Answer 15

Brain biopsy (rarely needed)

Question 16

What is the first line investigation of herpes encephalitis?

Answer 16

CSF PCR (95% sensitivity/specificity)
Might get a negative very early or late in disease

Question 17

How does aciclovir work?

Answer 17

Inhibits viral replication
(Competitive inhibitor or viral DNA polymerase)

Question 18

What is the mortality rate for herpes encephalitis?

Answer 18

20%

Question 19

What are the most common sequelae after herpes encephalitis?

Answer 19

Memory impairment
Behavioural changes
Dysphasia
Epilepsy

Question 20

What are the most common bacterial causes of meningitis?

Answer 20

Meningococcus
Pneumococcus

Question 21

How do viral and bacterial menigitidies differ in severity?

Answer 21

Bacterial - high morbidity and mortality
Viral - largely benign, treatment is symptom alleviation

Question 22

What are the symptoms of bacterial meningitis?

Answer 22

Headache
Fever
Meningismus (neck stiffness)
Sensory alteration
Vomiting
Seizures

Question 23

What are risk factors for pneumococcal meningitis?

Answer 23

Very young or old
Immunocompromised - asplenic
Alcoholism and malnutrition
Chronic disease (diabetes, kidney disease)
Base of skull fracture (entry point)

Question 24

How would you investigate for pneumococcal meningitis?

Answer 24

Blood cultures
CSF if not contraindicated

Question 25

What is the treatment for pneumococcal meningitis?

Answer 25

Cephalosporin
Further antibiotics if risk of resistance

Question 26

What is a useful adjunct to antibiotics for meningitis treatment?

Answer 26

Steroids (dexamethasone)

Question 27

What is an emerging infection?

Answer 27

Not previously recognised by medical science

or

Have jumped a species barrier

or

Have transplanted to a discrete geographical area where previously not found