CNS infections

Question 1

What is the blood-brain barrier?

Answer 1

barrier systems that separate the brain and CSF from the blood and prevent diffusion of electrolytes, fluids and substances from the blood into the CSF

Question 2

What produces the CSF?

Answer 2

choroid plexus

Question 3

How does meningitis affect CSF pressure?

Answer 3

causes rapid increases in CSF pressure resulting in brain herniation causing respiratory depression + death

Question 4

What does CSF look like?

Answer 4

clear
colourless

Question 5

How many cells and of what type are normal in CSF?

Answer 5

CSF is acellular
<5 WBCs + <5RBCs are normal in lumbar puncture CSF sample

Question 6

What can cause raised CSF protein?

Answer 6

CNS infections
SAH
traumatic tap
neoplastic meningitis
obstruction of CSF flow

Question 7

What can cause low CSF glucose?

Answer 7

bacterial meningitis

Question 8

What can cause low CSF glucose?

Answer 8

some viral infections:
- mumps
- herpes simplex
- herpes zoster
- lymphocytic choriomeningitis
- enteroviruses

TB
syphilis
fungal CNS infections

Question 9

What can cause CSF oligoclonal bands?

Answer 9

usually seen in MS
CNS infections
tumours
autoimmune diseases
lymphoproliferative diseases

Question 10

When is CSF xanthrochromia seen?

Answer 10

SAH - at least 6 hours after onset of thunderclap headache

Question 11

How do infections of the CNS occur?

Answer 11

direct innoculation (rabies, tetanus toxin)
haematogenous dissemination
contiguous spread (otitis media)

Question 12

Name some acute CNS infections

Answer 12

meningitis
encephalitis
brain abscess/subdural empyema
acute myelopathy = spinal epidural abscess, TB, poliomyelitis
cerebral malaria
toxin-mediated = botulism, tetanus

Question 13

What specific questions should be asked in suspected CNS infection?

Answer 13

occupation
travel
vaccination/prophylaxis
pregnancy
immune-competent/immune-suppressed
sexual behaviour
IV drug abuse
comorbidities (DM, cardiac disease, neurosurgery)
tick/animal exposure

Question 14

What is Kernig’s sign?

Answer 14

passive resistance to knee extension from flexed knee and thigh position

reflects irritation of nerve roots by inflamed meninges

Question 15

What is Brudzinski’s sign?

Answer 15

involuntary flexion of hips/knees with abrupt neck flexion

reflects irritation of nerve roots by inflamed meninges

Question 16

Lumbar puncture contraindications/CT needed first

Answer 16

raised intracranial pressure (hypertension, bradycardia, papilloedema)

focal neurological deficits

dilated/poorly reactive pupil (3rd nerve palsy)

coma or deteriorating LOC

signs of posterior fossa lesion (dysarthria, ataxia)

local sepsis

coagulopathy

seizures

immunocompromised

Question 17

Commonest causes of bacterial meningitis

Answer 17

neisseria meningitidis
streptococcus pneumoniae

Question 18

Commonest cause of bacterial meningitis in immunocompromised individuals

Answer 18

streptococcus pneumoniae
listeria monocytogenes
gram negative bacteria

Question 19

Symptoms and signs of acute infectious meningitis

Answer 19

triad of headache, fever, and neck stiffness
photophobia, rash (meningococcocaemia), vomiting, altered LOC

focal neurological deficits

Question 20

Subtle signs of meningitis in neonates

Answer 20

altered LOC
irritability
lethargy
weak suck
high pitched cry
vomiting
diarrhoea
fever
hypothermia
bulging fontanelle
jaundice

neck stiffness and fever may be absent

Question 21

Subtle signs of meningitis in the elderly

Answer 21

lethargy
obtundation (slowed response to stimulation)
fever and neck stiffness may be absent

Question 22

Who is at risk of pneumococcal meningitis?

Answer 22

splenectomy/splenic dysfunction
alcoholism
pneumonia
otitis media
paranasal sinusitis
CSF leaks
reduced humoral immunity eg. multiple myeloma

Question 23

Neurological complications of pneumococcal meningitis

Answer 23

venous sinus thrombosis
stroke
hydrocephalus
coma
seizures
focal neurological deficit

Question 24

Empiric treatment of bacterial meningitis

Answer 24

Cefotaxime IV 2g 6-hourly or Ceftriaxone 2g 12-hourly
+
Dexamethasone IV 10mg qds
+
Amoxicillin 2g 4-hourly for patients 60 years and over, immunocompromised, diabetes mellitus or alcohol misuse
+
Vancomycin IV or Rifampicin PO/IV for patients who have travelled recently to a country with prevalent penicillin-resistant pneumococcus

Question 25

Empiric treatment of bacterial meningitis - penicillin allergy

Answer 25

Chloramphenicol IV 25mg/kg 6-hourly
+
Dexamethasone IV 10mg qds
+
Co-trimoxazole IV 10-20mg/kg of the trimethoprim component in 4 divided doses for patients 60y +, immunocompromised, diabetes, or alcohol misuse
+
Vancomycin IV or Rifampicin PO/IV if travel to penicillin-resistant area

Question 26

What is a brain abscess?

Answer 26

infection of brain parenchyma

Question 27

What is a subdural empyema?

Answer 27

infection between dura and arachnoid mater

Question 28

What can cause brain abscesses/subdural empyemas?

Answer 28

trauma
neurosurgery
local infection (otitis media, dental, paranasal sinusitis, bacterial meningitis, orbital cellulitis)

Question 29

What is encephalitis?

Answer 29

part of meningoencephalitis
direct invasion of brain (rabies, HSV)
secondary immunological response to infection or immunisation (para- and post-infectious encephalitis)

Question 30

Encephalitis causes

Answer 30

viral eg HSV
bacterial eg ricketsial, typhus, syphilis
parasitic eg malaria

Question 31

Signs and symptoms of HSV1 encephalitis

Answer 31

fever
confusion
depressed LOC
seizures
focal neurological deficits - anosmia, hallucinations, dysphasia, hemiparesis, memory loss

Question 32

HSV1 encephalitis treatment

Answer 32

IV acyclovir