CNS Infections and Meningitis Flashcards
What are the 4 modes to entry for CNS infections?
- Haematogenous spread
- Direct implantation - via instrumentation
- Local extension - secondary to established infections
- PNS into CNS
Most frequent route of entry for pathogens causing CNS infections?
Haematogenous
What is meningitis?
Region inflamed
Signs + Sx
Causative agents
Inflamed: Meninges + CSF
Signs + Sx: Fever, headache, stiff neck, usually some disturbance of brain function.
Causative agents: Neisseria meningitidis, Streptococcus pneumoniae, Haemophilus influenzae, TB, Various viruses, Cryptococcus neoformans
What is encephalitis?
Region inflamed
Signs + Sx
Causative agents
Inflamed: Brain parenchyma
Signs + Sx: Disturbance of brain function
Causative agents: Rabies virus, arboviruses, Trypanosoma species, Prions, Amoeba.
What is myelitis?
Region inflamed
Signs + Sx
Causative agents
Inflamed: Spinal cord
Signs + Sx: Disturbance of nerve transmission
Causative agents: Poliovirus
What is neurotoxin?
Region inflamed
Signs + Sx
Causative agents
Inflamed: CNS + PNS
Signs + Sx: Paralysis, rigid (tetanus) or flaccid (botulism)
Causative agents: Clostridium tetani, Clostridium botulinum
What is meningoencephalitis?
Inflammation of meninges + brain parenchyma
How does meningitis cause neurological damage?
- Direct bacterial toxicity.
- Indirect inflammatory process + cytokine release + oedema.
- Shock, seizures, + cerebral hypoperfusion.
What is the prognosis of meningitis?
Mortality ~ 10%
Morbidity ~ 5% neurological sequelae, mainly sensorineural deafness
What are the three classifications of meningitis? What are the usual causative organisms?
- Acute: bacterial
- Chronic: TB, Spherocytes, Cryptococcus
- Aseptic: acute viral
What are 8 signs and symptoms of meningitis?
- Vomiting
- Fever
- Headache
- Stiff neck
- Light aversion
- Drowsiness
- Joint pain
- Fitting
What are the 6 most common causes of acute meningitis?
- Neisseria meningitidis
- Streptococcus pneumoniae
- Haemophilus influenzae
- Listeria monocytogenes
- Group B Streptococcus
- Escherichia coli
Which organism causes meningococcal meningitis?
Neiserria Meningitidis
Which organism causes pneumococcal meningitis?
Streptococcus penumoniae
What are the 3 most common causes of meningitis in the neonate (4w)?
Group B Streptococcus
Escherichia coli
Listeria monocytogenes
What are the 3 most common causes of meningitis in children/ young adults?
Neiserria Meningitidis
Haemophilus influenzae (rare in vaccinated countries)
Streptococcus pneumoniae
What are the 3 most common causes of meningitis in over 50s?
Neiserria Meningitidis
Streptococcus pneumoniae
Listeria monocytogenes
What are features of infection with N. Meningitidis?
Infectious cause of childhood death in all countries.
Transmission is person-to-person, from asymptomatic carriers.
Through nasopharyngeal mucosa in a susceptible individual
Pathogenic strains are found in only 1% of carriers.
Cause infections in <10d
What is a classical feature of meningococcal meningitis?
Nonblanching rash (petechial or purpuric) develops in 80% of children.
A maculopapular rash remains in 13% of children
No rash occurs in 7%.
When do cases of N.meningitidis peak? What vaccines are available?
Winter
A, C, Y + W135
What are links between meningitis and septicaemia in those with N. meningitidis?
- 50% of cases have meningitis
- 7-10% have septicemia
- 40% have septicemia AND meningitis
Why is the clinical difference between meningitis and septicaemia important?
Patients who present with shock are treated differently than patients who present primarily with increased intracranial pressure (ICP).
Meningitis: LP indicated
Septicaemia with a bleeding diathesis + clotting deranged: LP CONTRAINDICATED
Which 4 processes produce the clinical spectrum of septicaemia?
Capillary leak: Albumin + other plasma proteins leads to hypovolemia.
Coagulopathy: Leads to bleeding + thrombosis.
* Endothelial injury results in platelet-release reactions
* The protein C pathway.
* Plasma anticoagulants.
Metabolic derangement: Particularly acidosis
Myocardial failue: + multi-organ failure.
What is present on the CT scan of a patient with TB meningitis?
Enhancement in the basal cistern + meninges, with dilatation of the ventricles.
Give 5 features of chronic tuberculosis meningitis?
Incidence: 544 per 100,000 pop. in Africa.
More common in immunosuppressed.
Mortality: 5.5 per 100,000
Involves the meninges + basal cisterns of the brain + spinal cord.
Can result in tuberculous granulomas, tuberculous abscesses, or cerebritis.
What does a tuberculosis abscess look like on a CT head?
Enhancing thick-walled abscess.
What are 6 features of aseptic meningitis?
Most common infection of the CNS.
Patients with aseptic meningitis have headache, stiff neck, + photophobia.
A nonspecific rash can accompany these Sx
Enteroviruses: Coxsackievirus group B + echoviruses are responsible for 80-90% cases in which a causative organism of aseptic meningitis is identified.
Most frequently occurs in <1y/o
Clinical course is self-limited + resolves in 1-2w.
How is encephalitis transmitted?
Transmission is commonly either person to person, or through vectors:
- Mosquitoes
- Lice
- Ticks
What are some causative organisms of encephalitis?
Various viridae from Togavirus, Flavivirus, + Bunyavirus families.
But, West Nile Virus is becoming a leading cause of encephalitis internationally.
What are 4 non viral causes of encephalitis?
Bacterial encephalitis:
* Listeria monocytogenes
Amoebic encephalitis:
* Naegleria fowleri: Habitat – warm water
* Acanthamoeba species, + Balamuthia mandrillaris: Brain abscess, aseptic or chronic meningitis.
What is a parasitic cause of encephalitis? How is it transmitted? How does it manifest?
Toxoplasmosis
Obligate intracellular protozoal parasite, Toxoplasma gondii.
Via oral, transplacental route or organ transplantation.
Severe infection in immunocompromised patients.
Affected organs inc. gray + white matter of brain, retinas, alveolar lining of the lungs, heart, + skeletal muscle.
What is full of toxoplasma gondii?
Kitten poo
From which 5 conditions/ sites can infection spread to cause a brain abscesses?
- Otitis media
- Mastoiditis
- Paranasal sinuses
- Endocarditis
- Haematogenously
What are 7 causative organisms of a brain abscess?
- Streptococci (both aerobic + anaerobic)
- Staphylococci
- Gram -ve organisms (esp in neonates)
- Mycobacterium tuberculosis
- Fungi
- Parasites
- Actinomyces + Nocardia species
What can cause spinal infections? What may this lead to if left untreated?
Pyogenic vertebral osteomyelitis is a common form of vertebral infection.
Direct open spinal trauma, from infections in adjacent structures, from hematogenous spread of bacteria to a vertebra.
Untreated: permanent neurologic deficits, significant spinal deformity, or death.
What are 7 risk factors of spinal infections?
- Advanced age
- Intravenous drug use
- Long-term systemic steroids
- Diabetes mellitus
- Organ transplantation
- Malnutrition
- Cancer
What are investigations for CNS infections?
MRI is superior to CT scanning in detecting parenchymal abnormalities e.g abscesses + infarctions.
CNS infections:
* CSF sample
* Brain tissue
Blood culture
Blood PCR
Throat swab
What does this CSF study represent?
Appearance: Clear
Cells x 106/l: 0-5 leukocytes
Gram stain: Negative
Protein g/l: 0.15-0.4
Glucose mmol/l: >60% blood glucose level
Normal
What does this CSF study represent?
Appearance: Turbid
Cells x 106/l: 100-2000 polymorphs
Gram stain: Positive results
Protein g/l: 0.5-4.0
Glucose mmol/l: <60% blood glucose level
Purulent meningitis
Polymorphic nuclei in neutrophils indicate bacterial cause
DDx:
Bacterial meningitis
* ?Meningococcus
* ?Pneumococcus
* ?Listeria
What does this CSF study represent?
Appearance: Clear or slightly turbid
Cells x 106/l: 15-500 lymphocytes
Gram stain: Negative
Protein g/l: 0.5-1.0
Glucose mmol/l: >60% blood glucose level
Aseptic meningitis
DDx:
- Viral meningitis
- Partially abx treated bacterial meningitis
- Encephalitis
- Brain abscess
- TB/fungal meningitis
What does this CSF study represent?
Appearance: Clear or slightly turbid
Cells x 106/l: 30-500 lymphocytes or some polymorphs
Gram stain: Negative
Protein g/l: 1.0-6.0
Glucose mmol/l: <60% blood glucose level
Tuberculosis meningitis
DDx:
- TB meningitis
- Brain abscess
- Cryptococcal meningitis
A 20 year old woman presents with headache and neck stiffness. What is the causative pathogen?
Gram positive cocci
Pneumococcus
A 18 year old man present with headache and neck stiffness. What is the causative pathogen?
Gram negative cocci
Meningococcus
A 65 year old presents with headache and neck stiffness. What is the causative pathogen?
Gram positive rod
Listeria
A 45 year old presents with headache and neck stiffness. What is the causative pathogen?
Ziehl-Neelsen stain
TB
A 35 year old HIV+ man presents with headache and neck stiffness. What is the causative pathogen?
Indian ink stains
Cryptococcus
What are 6 limitations of diagnostics in CNS infections?
MRI oedema pattern + moderate mass effect cannot be differentiated from tumor/ stroke/ vasculitis in some patients.
Infections in early stages + serological tests.
Amount of CSF.
PCR techniques.
Methods to detect amoebic infections.
Availability of good laboratory technique.
What is the management of meningitis?
Ceftriaxone 2g IV bd
If >50y or immunocompromised add:
Amoxicillin 2g IV 4 hourly
What is the management of meningoencephalitis?
Aciclovir 10mg/kg IV tds
Ceftriaxone 2g IV bd
If >50y or immunocompromised add:
Amoxicillin 2g IV 4hourly
What is the recommended therapy for S. Pneumoniae or N. Meningitidis?
Pen G 18-24 mu/d
or
Ampicillin 12 g/d
or
Ceftriaxone 4 g/d
or
Chloro 75-100 mg/kg/d
What is the recommended therapy for H. Influenzae?
Cefotaxime 12 g/d
or
Ceftriaxone 4 g/d
What is the recommended therapy for Group B Strep?
Pen G
or
Amoxicillin [plus aminoglycoside]
What is the recommended therapy for Listeria?
Amoxicillin 12 g/d [plus aminoglycoside]
What is the recommended therapy for Gram negative bacilli?
Cefotaxime 12 g/d
or
Ceftriaxone 4g/d
What is the recommended therapy for Pseudomonas?
Meropenem 6g/d
or
Ceftazidime 6g/d
What is the most common cause of encephalitis in the UK?
HSV-2
