CNS infections Flashcards
What is the blood-brain barrier?
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
What produces the CSF?
choroid plexus
How does meningitis affect CSF pressure?
causes rapid increases in CSF pressure resulting in brain herniation causing respiratory depression + death
What does CSF look like?
clear
colourless
How many cells and of what type are normal in CSF?
CSF is acellular
<5 WBCs + <5RBCs are normal in lumbar puncture CSF sample
What can cause raised CSF protein?
CNS infections
SAH
traumatic tap
neoplastic meningitis
obstruction of CSF flow
What can cause low CSF glucose?
bacterial meningitis
What can cause low CSF glucose?
some viral infections:
- mumps
- herpes simplex
- herpes zoster
- lymphocytic choriomeningitis
- enteroviruses
TB
syphilis
fungal CNS infections
What can cause CSF oligoclonal bands?
usually seen in MS
CNS infections
tumours
autoimmune diseases
lymphoproliferative diseases
When is CSF xanthrochromia seen?
SAH - at least 6 hours after onset of thunderclap headache
How do infections of the CNS occur?
direct innoculation (rabies, tetanus toxin)
haematogenous dissemination
contiguous spread (otitis media)
Name some acute CNS infections
meningitis
encephalitis
brain abscess/subdural empyema
acute myelopathy = spinal epidural abscess, TB, poliomyelitis
cerebral malaria
toxin-mediated = botulism, tetanus
What specific questions should be asked in suspected CNS infection?
occupation
travel
vaccination/prophylaxis
pregnancy
immune-competent/immune-suppressed
sexual behaviour
IV drug abuse
comorbidities (DM, cardiac disease, neurosurgery)
tick/animal exposure
What is Kernig’s sign?
passive resistance to knee extension from flexed knee and thigh position
reflects irritation of nerve roots by inflamed meninges
What is Brudzinski’s sign?
involuntary flexion of hips/knees with abrupt neck flexion
reflects irritation of nerve roots by inflamed meninges
Lumbar puncture contraindications/CT needed first
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
Commonest causes of bacterial meningitis
neisseria meningitidis
streptococcus pneumoniae
Commonest cause of bacterial meningitis in immunocompromised individuals
streptococcus pneumoniae
listeria monocytogenes
gram negative bacteria
Symptoms and signs of acute infectious meningitis
triad of headache, fever, and neck stiffness
photophobia, rash (meningococcocaemia), vomiting, altered LOC
focal neurological deficits
Subtle signs of meningitis in neonates
altered LOC
irritability
lethargy
weak suck
high pitched cry
vomiting
diarrhoea
fever
hypothermia
bulging fontanelle
jaundice
neck stiffness and fever may be absent
Subtle signs of meningitis in the elderly
lethargy
obtundation (slowed response to stimulation)
fever and neck stiffness may be absent
Who is at risk of pneumococcal meningitis?
splenectomy/splenic dysfunction
alcoholism
pneumonia
otitis media
paranasal sinusitis
CSF leaks
reduced humoral immunity eg. multiple myeloma
Neurological complications of pneumococcal meningitis
venous sinus thrombosis
stroke
hydrocephalus
coma
seizures
focal neurological deficit
Empiric treatment of bacterial meningitis
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
Empiric treatment of bacterial meningitis - penicillin allergy
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
What is a brain abscess?
infection of brain parenchyma
What is a subdural empyema?
infection between dura and arachnoid mater
What can cause brain abscesses/subdural empyemas?
trauma
neurosurgery
local infection (otitis media, dental, paranasal sinusitis, bacterial meningitis, orbital cellulitis)
What is encephalitis?
part of meningoencephalitis
direct invasion of brain (rabies, HSV)
secondary immunological response to infection or immunisation (para- and post-infectious encephalitis)
Encephalitis causes
viral eg HSV
bacterial eg ricketsial, typhus, syphilis
parasitic eg malaria
Signs and symptoms of HSV1 encephalitis
fever
confusion
depressed LOC
seizures
focal neurological deficits - anosmia, hallucinations, dysphasia, hemiparesis, memory loss
HSV1 encephalitis treatment
IV acyclovir
