CNS Infections Flashcards
What are the different types of primary infections of the central nervous system?
- Meningitis
- encephalitis
- brain abscess
What is meningitis?
Meningitis is an infection of the protective membranes that surround the brain and spinal cord (meninges)
What is encephalitis?
An uncommon but serious condition in which the brain becomes inflamed (swollen)
What is brain abscess (cerebral abscess)?
An abscess caused by inflammation and collection of infected material within the brain tissue
Why is meningitis classed as a medical emergency?
It can be very serious if it is not treated quickly
it can cause life-threatening septicaemia and result in permanent damage to the brain or nerves
What is the difference between meningitis and meningoencephalitis?
Meningitis refers to an inflammatory process of leptomeninges and CSF
meningoencephalitis refers to inflammation of the meninges and brain parenchyma
How can meningitis be classified?
- Acute pyogenic- usually bacterial meningitis
- aseptic - usually viral meningitis, lymphocytic pleocytosis
- chronic - mycobacterium tuberculosis (TBM), spirochetes (neurosyphillis), cryptococcus neoformans
How is the onset of chronic meningitis defined?
Chronic meningitis has an onset measured in weeks to months
it is generally defined when symptoms, signs and the CSF remain abnormal for at least 4 weeks
What is the major cause of aseptic meningitis syndrome?
What does this mean?
Viruses are the major cause of the aseptic meningitis syndrome
this is used to define any meningitis (infectious or non infectious), particularly one with a lymphocytic pleocytosis, for which a cause is not apparent after initial evaluation and routine stains and cultures of CSF
What are the 4 different ways in which infectious agents can enter the CNS?
Haematogenous spread:
- this is the most common and usually via arterial route
- can be retrograde (veins)
Direct implantation:
- most often is traumatic
- iatrogenic (rare)
- congenital (meningomyelocele)
Local extension:
- secondary to established infections
- most often from mastoid, frontal sinuses, infected tooth, etc.
Along peripheral nerves:
- usually viruses such as rabies & herpes zoster
What are the clinical features which suggest meningitis?
- Headache
- irritable
- neck stiffness
- photophobia
- fever
- vomiting
- varying levels of consciousness
- rash
Which groups may have a non-specific presentation of meningitis?
- Neonates
- elderly
- immunosuppressed
which organisms tend to cause meningitis in children < 1 month?
- Streptococcus agalactiae
- escherichia coli
- listeria monocytogenes
What organisms cause meningitis in a child aged between 1 to 23 months?
- Streptococcus pneumoniae
- Neisseria meningitidis
- Streptococcus agalactiae
- Escherichia coli
- haemophilus influenzae
Which organisms tend to cause acute bacterial meningitis in people aged 2-50 years?
- Streptococcus pneumoniae
- neissseria meningitidis
Which organisms tend to cause acute bacterial meningitis in people aged over 50?
- Streptococcus pneumoniae
- Neisseria meningitidis
- Listeria monocytogenes
- aerobic Gram negative bacilli
What is involved in the laboratory diagnosis of meningitis?
- Blood cultures
- lumbar puncture - CSF for microscopy, Gram stain, culture & biochemistry
- EDTA blood for PCR
What is the appearance and cells of normal CSF?
It is clear and colourless
cells are 0-5 lymphocytes cu mm
What does the CSF look like in bacterial meningitis?
The CSF is cloudy and turbid
Cells - 100-2000 polymorphs cu mm
there are high levels of protein and low levels of glucose
What does the CSF look like in “aseptic” / viral meningitis?
The CSF is clear but slightly cloudy
Cells - 10-500 lymphocytes cu mm
there is normal levels of both protein and glucose
What does the CSF look like in TB meningitis?
The CSF is clear but slightly cloudy
Cells - 10-500 lymphocytes cu mm
there are high levels of protein and low levels of glucose
What does the CSF look like in cryptococcal meningitis?
The CSF is clear
cells - 10-200 lymphocytes
protein is normal or slightly elevated
glucose is normal or slightly reduced
Who tends to suffer from viral meningitis?
How may it start?
It primarily affects children and young adults
it has milder signs and symptoms
it may start as a respiratory or intestinal infection, then viraemia
What type of cell is raised in the CSF in viral meningitis?
Do people recover?
CSF shows raised lymphocyte count (50-200/cu mm)
protein and glucose are usually normal
full recovery is expected
What are the causes of viral meningitis?
- Enteroviruses - Echo, Coxsackie A & B
- Paramyxovirus - mumps
- Herpes simplex, Varicella Zoster virus
- adenoviruses
- other - arboviruses, lymphocytic choriomeningitis, HIV
What is the onset of tuberculosis meningitis like?
Which group of people are more at risk?
It has an insidious onset
higher incidence in immigrant populations who come from countries with a higher incidence of TB
How severe are complications from tuberculosis meningitis?
High frequency of complications - cranial nerve palsies
delayed diagnosis makes complications more likely
what is the composition of the CSF like in tuberculosis meningitis?
CSF shows predominantly lymphocytic response but polymorphs also present
there is high protein
there is low / absent glucose
What is encephalitis?
What usually causes it?
Encephalitis is an acute inflammatory process affecting the brain parenchyma
viral infection is the most common and important cause
over 100 viruses are implicated worldwide
What are the symptoms of encephalitis?
What is the incidence?
- Fever
- headache
- behavioural changes
- altered level of consciousness
- focal neurological deficits
- seizures
incidence of 3.5 - 7.4 per 100,000 persons per year
What are the causes of viral encephalitis?
- Herpes viruses
- HSV-1 & HSV-2
- varicella zoster virus
- cytomegalovirus
- epstein-Barr virus
- human herpes virus 6
- adenoviruses
- influenza A
- enteroviruses, poliovirus
- measles, mumps & rubella viruses
- rabies
- arboviruses
- Japanese encephalitis virus
- St. Louis encephalitis virus
- West Nile encephalitis virus
What is herpes encephalitis?
what are the major effects of this and what may there be evidence of?
Most common cause of sporadic encephalitis in previously healthy individuals
may be evidence of herpes infection of skin / mucosae
causes severe haemorrhagic encephalitis affecting the temporal lobe
also focal signs and epilepsy features
How many cases of herpes encephalitis are there per year?
2-4 cases per million people per year
This may be acute infection, but more commonly there is reactivation of latent infection in the trigeminal nerve ganglion
What is the mortality like for herpes encephalitis?
How should it be treated?
30% mortality with treatment and 70% mortality without treatment
high mortality so treatment is needed urgently with aciclovir
What is meant by recurrent meningitis?
what must it be differentiated from?
- > 2 episodes of meningitis
- symptom-free intervals
- normal CSF between episodes
must be differentiated from chronic meningitis
What is rabies?
Why is it important to recognise?
Acute, progressive viral encephalitis
highest case fatality of any infectious disease
Why is rabies described as a viral zoonosis?
A zoonosis is an infectious disease caused by a pathogen that has jumped from non-human animals to humans
How does rabies cause infection?
How does it enter the body?
The virus enters through a bite
it grows at the trauma site for a week and multiplies
it then enters nerve endings and advances towards the ganglia, spinal cord and brain
the infection cycle is completed when the virus replicates in salivary glands
What are the clinical phases of rabies?
what symptoms are experienced during these phases?
Prodromal phase:
- fever, nausea, vomiting, headache, fatigue
- some experience pain, burning, tingling sensations at the site of the wound
Furious phase:
- agitation, disorientation, seizures, twitching, hydrophobia
Dumb phase:
- paralysed, disorientated, stuporous
- the dumb phase progresses to the coma phase, resulting in death
When does neurosyphilis arise?
Asymptomatic neurosyphilis can occur at any stage of syphilis
central nervous system invasion occurs early in infection in 30-40% of patients
early symptomatic forms occur from months to a few years
What are the symptoms of neurosyphilis?
How is it diagnosed?
- Acute meningitis
- meningovascular (stuttering stroke)
- general paresis
- tabes dorsalis
it is diagnosed by blood & CSF serology
What is a brain abscess?
A focal suppurative process within the brain parenchyma
(pus in the substance of the brain)
what are the 4 different ways in which a brain abscess can form?
- Direct spread from “contiguous suppurative focus” - e.g. from ear, sinuses, teeth
- haematogenous spread from a distant focus - e.g. endocarditis, bronchiectasis
- trauma - e.g. open cranial fracture, post-neurosurgery
- cryptogenic - no focus is recognised in 15-20% of cases
What types of pathogens are usually found within a brain abscess?
The bacteria responsible depend on the pathogenic mechanism involved
brain abscesses are often mixed (polymicrobial)
- streptococci (60-70%) e.g. streptococcus milleri
- staphylococcus aureus in 10-15%
- anaerobes
- Gram negative enteric bacteria
- others such as fungi, mycobacterium tuberculosis, toxoplasma gondii
What is the clinical presentation of brain abscess?
- Headache (most)
- focal neurological deficit (30-50%)
- fever (<50%)
- nausea, vomiting
- seizures
- neck stiffness
- papilloedema
What is involved in the management of a brain abscess?
Drainage is the treatment of choice, but small abscesses can be treated with antibiotics alone
- to urgently reduce intracranial pressure
- to confirm diagnosis
- to obtain pus for microbiological investigation
- to enhance efficiency of antibiotics
- to avoid spread of infection into the ventricles
What factors must be considered for antibiotic treatment of CNS infections?
Which antibiotics achieve therapeutic concentrations in intracranial pus?
- Physiological properties of blood-brain barrier & blood-CSF barrier are distinct
- penetration of drugs into CSF and brain tissue differ
- ampicillin, penicillin, cefotaxime, ceftazidime & metronidazole acheive therapeutic concentrations in intracranial pus
What type of steroid is used for CNS infections?
Dexamethasone
10mg IV given 15 minutes prior to antibiotics
shown to decrease morbidity & mortality in S.pneumoniae but not N.meningitidis
