MICRO: CNS infections and meningitis Flashcards
What are the 4 routes of pathogen entry into the CNS? What is the most common route of entry?
Routes of Pathogen Entry into the CNS – 4 routes of entry…
- Haematogenous (e.g. pneumococcus, meningococcus carriage may penetrate and seed) - MOST COMMON
- Direct implantation (e.g. trauma)
- Local extension (e.g. from the ear like swimmer’s ear)
- PNS into CNS (e.g. rabies after bite)
What is meningtitis? Its signs and symptoms? Its causative agents?
What is encephalitis? Its signs and symptoms? Its causative agents?
What is myelitis? Its signs and symptoms? Its causative agents?
What does neurotoxin infection affect? Its signs and symptoms? Its causative agents?
What is meningoencephalitis?
inflammation of the meninges and brain parenchyma
What is neurological damage caused by in meningitis? How common is it?
Neurological damage = 10% mortality, 5% neurological sequelae; sensorineural deafness)
Caused by:
- Direct bacterial toxicity
- Indirect inflammatory process and cytokine release and oedema (n.b. tight space, oedema = bad)
- Shock, seizures and cerebral hypoperfusion
How can you classify CNS infections?
- Classification:
- Acute (hours to days) - usually bacterial meningitis
- Chronic (days to weeks) - usually TB
- Aseptic (caused by viruses so there is no pus) - usually viral
In which group would you classify meningococcal meningitis?
Acute
What are the main 3 causes of acute meningitis?
- Neisseria meningitidis
- Streptococcus penumoniae
- Haemophilus influenzae
Also:
- Listeria
- GBS
- E.coli
Other causes below:
What are the other causes of meningitis in specific populations?
- Listeria monocytogenes - key cause of meningoencephalitis, old, pregnant,
- Group B Streptococcus - common in females, 1/3 of European women, can cause neonatal meningitis after birth
- Escherichia coli - biphasic in old people and neonates
What are the rash presentations in N. meningitidis?
- Non-blanching rash (80% of children)
- Maculopapular rash (13% of children)
- No rash (7% of children)
What are the other phenotypes of N. meninitidis? Why is it important to distinguish?
- 50% have meningitis,
- 7-10% have septicaemia,
- 40% have meningitis AND septicaemia
- Important to distinguish as treatment for shock and raised ICP is different *
What four processes govern the clinical presentation 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
How many serotypes of N meningitidis? How is it acquired?
- ≥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
Give an examples of chronic meningitis.
Tuberculous chornic meningitis
What are the complications of tuberculous chronic meningitis?
- Tuberculous granulomas
- Tuberculous abscesses (i.e. enhancing thick-walled abscesses) in the brain
- Cerebritis
Below: normal brain vs TB brain vs tuberculoma (leading to death)
How does tuberculous chronic meningitis present? What is the mortality?
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
What is the most common infection of the CNS?
Aseptic meningitis
How does aseptic meningitis present? What are the two most common causes?
- Presentation: headache, stiff neck, photophobia
- A non-specific rash may accompany these symptoms
Organisms (80-90% of organisms) – VIRAL:
- Enteroviruses - Coxsackie group B and Echoviruses
- Herpes simples (1&2)
Who is most affected by aseptic meningitis? What is the management?
Usually occurs in children <1 year
Self-limiting disease that resolves in 1-2 weeks
Other than enteroviruses and herpes simplex, what are the other causes of meningitis?
What are the main modes of transmission of encephalitis?
Transmission is pretty much ALL haematogenous:
- Person-to-person
- Vectors (e.g. mosquitoes, lice, ticks)
Which virus is becoming a leading cause of encephalitis worldwide?
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
What are the causes of non-viral encephalitis?
- Bacterial – Listeria monocytogenes
-
Amoeba (spread by direct extension through cribriform plates):
- Naegleria fowleri - habitat – warm water
- Acanthamoeba spp. & Balamuthia mandrillaris - brain abscess, aseptic & chronic meningitis
-
Toxoplasmosis (obligate intracellular protozoal parasite – Toxoplasma gondii):
- Spread via the faeco-oral, transplacental or organ transplant route
- Causes severe infection in immunocompromised patients
- Affected organs = grey & white matter of brain, retinas, alveolar lining of lungs, heart, skeletal muscle
What is the pathophysiology of brain abscesses?
- Cause death due to pressure-related issues
- Pathophysiology:
- Direct extension (e.g. otitis media, mastoiditis, para-nasal sinuses)
- Occasionally spread haematogenously (e.g. endocarditis)
What are the causative agents 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
How are spinal infections spread? What is a common type?
- 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
What are the complications of spinal infections?
- Permanent neurological deficits
- Significant spinal deformity
- Death
What are the risk factors for spinal infections?
- Age
- IVDU
- Long-term systemic steroids
- Diabetes mellitus
- Organ transplantation
- Malnutrition
- Cancer
(similar to those for getting endocarditis)
What investigations should be done for CNS infections?
- MRI>CT
- If CNS affected:
- CSF sample
- brain tissue - but rarely done
- Blood culture - very important as usually haematogenous spread, relies on no antibiotics given
- Throat swab
- Blood PCR - good if antibiotics given
Which imaging should be done to detect brain abscesses and infarctions?
Plain CT brain are useless at seeing brain abscesses
Enhancing lesions better seen on MRI BUT CT is more readily available
Describe the normal, purulent, aseptic and TB meningitis CSF presentations in terms of
- appearance
- cells
- gram stain/antigen tests
- protein g/l
- glucose mmol/l
- main differential
S pneumoniae because dark purple with gram stain which means gram positive
- Arranged as diplococci*
- NB: meningococci are gram -ve*
Gram negative diplococci seen
Many neutrophils present
No haemolysis
N meningitidis
Listeria monocytogenes
Gram positive rod
M tuberculosis
Ziehl-Neelsen stain seen (red and blue)
- Hx: MSM, 3/7 history
- High opening pressure on LP
Cryptococcus neoformans
- HOP pathogenomic of C. neoformans
- Occurs in immunocompromised people
- India ink stain used
- Cryptococcus is a yeast surrounded by capsule as shown
What are the 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
If you suspect CNS infections, what should you do within:
- 30mins
- 1-2 hours
- 24-48 hours
Initial doses of antibiotics should be given almost immediately. This can be changed a bit later.
What is the generic treatment for meningitis and meningo-encephalitis?
Specific treatments for some CNS infections:
Learn the appearance of these cells:
List some adjunctive mangement steps for CNS infections.
- Corticosteroids (do NOT give them without speaking to a specialist, but it can be useful for cerebral oedema)
- Repeat LP
- Public health – may need to be reported
