CNS Infections and Meningitis Flashcards
4 routes of Pathogen Entry into the CNS
Haematogenous (e.g. pneumococcus, meningococcus)
- MOST COMMON
- causes of aseptic meningitis include enterovirus and herpes (also transfers via haematogenous spread)
Direct implantation (e.. trauma)
Local extension (e.g. from the ear)
PNS into CNS (e.g. rabies)
Meningitis vs Encephalitis
- Meningitis = “I don’t know who the prime minister is” but all other AMTS fine
- Encephalitis = “Tony Blair is the prime minister and I’m in the secret service”
4 main symptoms once pathogens enter CNS
What is meningitis and meningoencephalitis
Meningitis = inflammatory process of the meninges and CSF
Meningoencephalitis = inflammation of the meninges and brain parenchyma
Neurological damage in meningitis
(10% mortality, 5% have neurological sequelae; sensorineural deafness) is caused by:
- Direct bacterial toxicity
- Indirect inflammatory process and cytokine release and oedema (n.b. tight space, oedema = bad)
- Shock, seizures and cerebral hypoperfusion
Classification of meningitis
- Acute (hours to days)
- Chronic (days to weeks)
- Aseptic (caused by viruses so there is no pus)
3 main causes of acute meningitis
Neisseria meningitidis
- ≥12 serotypes (90% = A, B, C); A, B, C, W and Y are vaccinated against
- Transmitted from person-to-person, from asymptomatic carriers
- Pathogenic strains are only found in about 1% of carriers
- Enters the body through the nasopharyngeal mucosa in a susceptible individual
- Causes infection in <10 days
- Non-blanching rash (80% of children)
- Maculopapular rash (13% of children)
- No rash (7% of children)
- 50% have meningitis, 7-10% have septicaemia, 40% have meningitis AND septicaemia
- Important to distinguish as treatment for shock and raised ICP is different *
- Pathogenic strains are only found in about 1% of carriers
Streptococcus pneumoniae
- Bimodal distribution (children, elderly)
Haemophilus influenzae
- Type B is immunised against
Other and rare causes of meningitis
Other causes:
- Listeria monocytogenes (key cause of meningoencephalitis)
- Group B Streptococcus (can cause neonatal meningitis)
- Escherichia coli (biphasic – old people and neonates)
Rare causes:
- TB, S. aureus, T. pallidum, Cryptococcus neoformans
4 processes of septicaemia
Capillary Leak – albumin and other plasma proteins leads to hypovolaemia
Coagulopathy – leads to bleeding and thrombosis (endothelial injury results in platelet release reactions, the protein C pathway and plasma anticoagulants are affected)
Metabolic Derangement – particularly acidosis
Myocardial failure – and multi-organ failure
Chronic meningitis presentation, epidemiology and complications
(e.g. Tuberculous chronic meningitis) – may take weeks to develop:
- Similar presentation to acute meningitis (fever, headache, neck stiffness) but lower mortality (0.000055%)
- More common in immunosuppressed patients
- Involves the meninges and basal cisterns of the brain and spinal cord with dilatation of ventricles
Complications:
- Tuberculous granulomas
- Tuberculous abscesses (i.e. enhancing thick-walled abscesses)
- Cerebritis
Aseptic meningitis
MOST COMMON infection fo the CNS
- Presentation: headache, stiff neck, photophobia
- A non-specific rash may accompany these symptoms
- Organisms (80-90% of organisms) – VIRAL:
- Coxsackie group B
- Echoviruses
Usually occurs in children <1 year
Self-limiting disease that resolves in 1-2 weeks
Aseptic meningitis
MOST COMMON infection of the CNS
- Presentation: headache, stiff neck, photophobia
- A non-specific rash may accompany these symptoms
- Organisms (80-90% of organisms) – VIRAL:
- Coxsackie group B
- Echoviruses
Usually occurs in children <1 year
Self-limiting disease that resolves in 1-2 weeks
Encephalitis transmission
- Transmission is pretty much ALL haematogenous:
- Person-to-person
- Vectors (e.g. mosquitoes, lice, ticks)
Causes of viral encephalitis
UK = HSV-2
WW = arboviruses
Importance of West Nile virus
-
IMPORTANT: West Nile Virus is becoming a leading cause of encephalitis worldwide
- Mainly transferred by mosquitoes and birds (European birds spend the winter in Southern Europe and Africa)
- West Nile Virus has spread across the USA but hasn’t reached the UK yet
Non-viral encephalitis examples
2 types of focal CNS infections
Brain Abscesses and Spinal infections
How does brain abscess cause death
what do brain abscesses look like on MRI
Death due to pressure-related issues
Brain abscess how does it infect
- Direct extension (e.g. otitis media, mastoiditis, para-nasal sinuses)
- Occasionally spread haematogenously (e.g. endocarditis)
Causative organisms for brain abscesses
Causative Organisms (Strep > Staph > gram -ve > other):
- Streptococci (anaerobic and aerobic)
- Staphylococci
- Gram-negative organisms (mainly in neonates)
- TB, fungi, parasites, actinomyces and Nocardia species
Most common form of spinal infections and route of spread
Pyogenic vertebral osteomyelitis is a common form of vertebral infection (e.g. staph and strep)
Spread via… direct open spinal trauma or it can spread haematogenously
Complications of untreated spinal infections
- Permanent neurological deficits
- Significant spinal deformity
- Death
RFs for spinal infections
- Age IVDU Long-term systemic steroids
- Diabetes mellitus Organ transplantation Malnutrition
- Cancer
Diagnostics for CNS infections
CSF results
Examples of pathogens
Gram +ve cocci
- S. Pneumonia
- A-haemolytic diplococcus
Gram +ve rod
- L. monocytogenes
Gram -ve cocci
- Gram-ve diploccocus
- N. meningitides
Examples of pathogens
Gram +ve cocci
- S. Pneumonia
- A-haemolytic diplococcus
Gram +ve rod
- L. monocytogenes
Gram -ve cocci
- Gram-ve diploccocus
- N. meningitides
Rare pathogen causing meningitis
- Hx: MSM, 3/7 history
- High opening pressure on LP
- HOP pathogenomic of C. neoformans
- Occurs in immunocompromised people
Limitations of diagnostics
- MRI oedema pattern and moderate mass effect cannot be differentiated from tumour or stroke or vasculitis
- Serology may not be useful in early stages of infection
- Difficulties obtaining sufficient CSF
- PCR techniques are expensive
- Methods to detect amoebic infections
- Availability of good laboratory technique
Mx approach to patients with possible CNS infection
Menignitis vs meningo-encephalitis treatment
-
Ceftriaxone is good at killing N. meningitidis, S. pneumoniae, HiB and E. coli
- However, Ceftriaxone does NOT cover Listeria monocytogenes this requires amoxicillin
- Hence why, if >50yo, treat with amoxicillin
Specific therapies to meningitis pathogens
Adjunctive therapy
- Level of care required
- Corticosteroids (do NOT give them without speaking to a specialist, but it can be useful for cerebral oedema)
- Repeat LP
- Public health
Key take-home messages
- Act fast in CNS infections
- Take appropriate samples
- Anticipate the likely microbiology – this directly impacts empirical antimicrobial therapy
- Learn the CSF interpretation table by rote – this directly impacts refining the antimicrobial therapy
