CNS infections Flashcards
what is the CNS impermable to
large molecules
what is the main route of invasion for pathogens into the CNS
blood vessels
what 2 barriers protect theCNS against pathogen invasion
blood-brain barrier; blood-CSF barrier
how can pathogens traverse the protective barriers of the brain (3)
- growing across - infecting the cells that comprise the barrier;
- being passively transported across in intracellular vacuoles;
- being carried across by infected white blood cells
blood brain barrier structure
- thick basement membrane;
- astrocyte footplates;
- endothelium (no fenstrations)
what produces CSF
choroid plexus
blood CSF barrier structure
- endothelium (fenstrated);
- basement membrane;
- choroid plexus epithelium
what is the most common route of invasion to the brain (+ examples)
blood-borne e.g. polioviruses, neisseria meningitidis
osteomyelitis of the masteoid can lead to what condition
meningitis
examples of organisms that invade from peripheral nerves (3)
herpes simples; varicella zoster; rabies
what might a high opening pressure in a lumbar puncture indicate
inflammation in the brain (CSF under high pressure)
normal CSF charcteristics (3)
- clear and colourless;
- viscosity equal to water;
- acellular (up to 5 RBC and 5 WBCs are normal but more is abnormal)
when is a clot seen in lumbar puncture
in a traumatic tap (not SAH)
what does viscous CSF indicate
increased protein content
should antibodies be present in CSF
no
2 further investigations if CSF microscopy and cultures come back negative
PCR, serology
low CSF glucose level is indicative of what, and why
indicates the presence of bacteria as they feed on glucose
what is an important virulence factor in bacterial meningitis
polysaccharide capsules
what organisms most commonly cause bacterial meningitis in those <1mo (4)
- group B strep;
- E.coli;
- Listeria moncytogenes;
- aerobic gram -ve bacteria
what organisms most commonly cause bacterial meningitis in those 1-23mo (5)
- group B strep;
- E.coli;
- H.influenzae;
- streptococcus pneumoniae;
- neisseria meningitidis
what organisms most commonly cause bacterial meningitis in those 2-50yro (2)
- S. Pneumoniae;
- N. meningitidis
what organisms most commonly cause bacterial meningitis in those 50+ (4)
- S. Pneumoniae;
- N. meningitidis;
- L. monocytogenes;
- aerobic gram -ve bacteria
what organisms most commonly cause bacterial meningitis in those with head trauma (3)
- s. aureus;
- aerobic gram -ve bacteria;
- P. acnes;
what special feature allows for its specialised virulence mechanism and also dictates the serotype
an antigenic polysaccharide capsule
8 clinical features of a meningococcal meningitis
- haemorrhagic skin rash;
- sudden onset sore throat;
- sudden onset headache;
- sudden onset drowsiness;
- fever;
- irritability;
- neck stiffness;
- photophobia
neisseria meningitidis onset and who it affects
acute onset (6-24hrs); presents with a skin rash in children and adolescents
haemophilus influenzae onset and who it affects
less acute onset (1- 2 days); affects children <5yrs
streptococcus pneumoniae meningitis onset and who it affects
acute onset that may follow pneumonia or septicaemia (in elderly); affects children <2yrs and the elderly
what CSF test can be ueeful in determining a bacterial infection
serum glucose : CSF glucose ratio (low) - as bacteria breakdown glucose
why might antibody testing not be a useful test for meingitis
the infection is too acute for an antibody response to be detectable
Mgx of acute meningitis (6)
- alert the lab that a CSF sample is arriving;
- start antibiotic + antiviral + antifungal;
- isolate
- narrow down the medical management when results from the lab have arrived;
- steroids (if pneumococcus);
- contact tracing - give one off dose of prophylactic Abx to close contacts
when are the MenB vaccines given (3)
2 months; 4 months; 12 months
when is the MenACWY vaccine given
14 yrs
prior to infecting the CNS, where must S.pneumoniae colonise first
nasopharyns mucus; mucosal epithelium
how does S.pneuomniae enter the CSF
through white cells or vacuoles
what meningitis causing organism is the most deadly
pneumococcal
what histopathological changes can be seen in meningitis (4)
haemorrhages; neutrophilic degeneration; abscess formation; infarctions
what is the most common type of meningitis
viral
viral meningitis presentation (4)
headache; fever; photophobia; reduced neck stiffness (compared to bacterial)
vrial meningitis CSF macro/microscopy
macro - clear
mirco - cells are mainly lymphocytes (although polymorphonucler leukocytes may be dominant in early phases)
what commonly causes encephalitis
viruses
how does the meninges appear in a CT scan of encephalitis
not inflamed
infectious differentials for encephalitis (types)
- viral (herpes simplex, measles, mumps etc.);
- bacterial (neisseria meningitidis, H.influenzae etc.);
- parasitic (malaria etc.);
- fungal (cryptococcal);
- para/post infectious (acute disseminated encephalomyelitis)
5 non-infectious differentials for encephalitis
- vascular (SAH,SDH etc.);
- neoplastic/ paraneoplastic;
- metabolic (renal encephalopathy, toxins etc.);
- epilepsy;
- antibody mediated encephalitis
infection of blood vessels –> infection of CNS cells pathway
virus/infected leukocyte localises in blood vessels –> pathogen leaves blood vessels –> sensitised T cells release cytokines –> cytokines induce infiltration of mononuclear cells –> infection of neural cells –> further spread and destruction of infected neural cell
3 causes of recurrent bacterial meningitis
- basal skull defects;
- recurrent aseptic meningitis (usually HSV2 and hx of recurrent genital lesions);
- congenital dermal sinus
what causes brain abcesses
infection with bacteria or fungi
examples bacterial spread from nearby tissue infection causing brain abcesses (3)
- persistant middle ear infection;
- sinusitis;
- mastoiditis (infection of bone behind the eye)
3 ways bacteria can spread to cause brain abcesses
- via neraby tissue infection;
- haematogenous spread;
- neurosurgical inoculation
3 main microorganisms responsible for brain abscess formations
- streptococcus pneumoniae, H.influenzae or candidia from nearby ENT infection;
- Staphylococcus species via iatrogenic infection;
- any other microorganism via haematogenous spread
examples of fungal causes of brain abscesses
aspergillus; candida; cryptococcus; mucorales
examples of protazoal causes of brain abcesses
toxoplasma gondii; entamoeba histolytica; paragonimus
what can aid in the diagnosis of toxoplasmosis
serological tests
what common conditions increases the risk of brain abscesses
diabetes
brain abscess Mgx
- surgical excision/drainage;
- prolonged antimicrobial therapy (4-8 weeks)
why is it essential to chose the correct antobiotics for CNS infections
antibiotics are generally large molecules which cannot cross the BBB - only specific ones can cross and actually enter the the CNS
what is the most critical factor in survival for bacterial menigitis
door-to-antibiotics time
what abx should be given if presenting out of hospital w a purpuric rash
ceftriaxone 1g (if >12yrs);
otherwise give benzyl penicillin
encephalitis presentation
fever, headaches, focal neurological deficits, seizures, and altered or decreased level of consciousness
meningitis neck stiffness (rather than ddx neck stiffness)
front-back neck stiffness rather than rotational
lumbar puncture contraindications (9)
- raised ICP
- focal neurological defecits
- dilated/poorly reactive pupil (CN III palsy)
- coma/deteriorating conciousness
- signs of posterior fossa lesion (dysarthria, ataxia)
- local sepsis
- coagulopathy
- seizures
- immunocompimised`
when is lumbar puncture the test of choice
progressive headache over several days, photophobia, awake +talking
3 things that increase the risk of meningitis
- pneumonia
- otis media
- alcohol
why do you not have to treat viral meningitis
virus doesn’t spread to brain, just remains on meninges
TB meningitis presentation
- subacute/chronic onset;
- mild headache;
- low grade grumbling fever;
- CN palsies
which lobes are greatly affected in encephalitis
temporal lobes
encephalitis treatment
- IV FLUIDS
- anti-inflammatory meds (steroids etc.)
- anti-convulsatns (phenytoin)
- acylovir (or other to treat underlying cause)
