16 Infections of the CNS Flashcards
define meningitis
a serious disease in which there is inflammation of the meninges, caused by viral or bacterial infection, and marked by intense headache and fever, sensitivity to light, and muscular rigidity.
route of infection in meningitis (4)
1 blood-borne, commonest
2 parameningeal suppuration, meaning from infection in tissues surrounding the brain e.g. ear (otitis media) and sinuses (sinusitis)
3 direct spread through defect in the dura, CSF leak, if leaking out then there’s a route for organisms to go in e.g. post surgery, trauma
4 direct spread through the cribiform plate (rare)
complications of meningitis
death subdural collection- pressure cerebral vein thrombosis hydrocephalus, build up of CSF, may need long term drainage deafness, 9-15% (Hib) convulsions visual/motor/sensory deficit
causes of bacterial meningitis and age groups (5)
Neisseria meningitidis= children/young adults (vaccines have reduced this)
Streptococcus pneumonia= elderly and children<2 (usually pneumonia but can cause meningitis if into CSF)
Haemophilus influenzae type b, Hib= children<5 (vaccines have reduced this)
Escherichia coli= neonates
Listeria monocytogenes= neonates/immunocompromised (good at crossing placenta, high risk foods like unpasteurised cheeses and pate)
why do we worry about infection getting into CSF
normally doesn’t have bacteria so don’t have response ready there to clear it
blood brain barrier, prevents toxic things getting in but makes it hard to get drug across to treat infection
what drugs are more likely to cross BBB
small lipophilic compounds
inflammatory process in meningitis
triggered by components in cell wall
migration of neutrophils to the CSF, release of proteolytic products and toxic O radicals, which damaged vascular endothelium reducing BBB, leaking of CSF
take advantage of this in treatment so can get drug through damaged BBB
pathogenesis of bacterial meningitis
organisms commonly sit in nasopharynx
get into blood stream, bacteraemia, through pili (binding) endocytosis and separating junctions (increased in immunosuppressed and smokers, mucosal damage allowing invasion)
in blood stream, immune system usually clears it but if doesn’t then they start to multiply, causing inflammatory cascade leading to sepsis
OR survives in blood stream and gets into CSF
now in site where takes a while for inflammatory cascade to happen, multiples
infection in subarachnoid space
symptoms of meningitis
global headache
neck and back stiffness- specific for this
nausea and vomiting due to raised intracranial pressure
photophobia- sensitivity to bright lights
these symptoms can occur in other conditions like UTIs, subarachnoid haemorrhage (usually sudden headache not gradual), malignancy
meningitis symptoms in infants
typical signs not often present flaccid fever and vomiting often the only sign strange cry convulsions
physical signs of meningitis
don’t need them, mainly due to ongoing blood stream infection
fever
rash petechial/purpuric, bleeding into skin because of damage, take sample GLASS TEST
meningeal irritation
- kernig’s positive due to hamstring spasm
- neck stiffness, unable to put chin on chest
- brudzinskis sign- neck flexion causes flexion of hip and knees
most important test in meningitis suspicion
lumbar puncture
most rapid test
distinguish between bacterial and viral causes
BUT risk of herniation of bottom of the brain due to rise in pressure, do neuroimaging first if has long history, focal neurology, drowsy etc
CSF changes in meningitis
raised leucocytes reduced glucose in bacterial and TB not viral in bacterial- raised neutrophils in viral and TB- raised lymphocytes raised proteins
what is meningococcal disease
Meningococcal is a bacteria that enters the body, however
meningococcal disease does not always lead to meningitis. It only
leads to meningitis if the bacteria affects the meninges of the brain
risk factors for poor outcomes in meningitis
older otitis media or sinusitis absence of rash tachycardia positive blood culture low CSF fluid white cell count
how is meningitis managed (5)
antibiotics
adequate oxygenation to protect brain
prevention of hypoglycaemia and hyponatraemia
anticonvulsants
decrease intracranial hypertension in extreme setting
ideal antibiotic features for meningitis (4)
bactericidal
good activity against likely pathogens
sufficient penetration into CSF at non-toxic doses
low levels of endotoxin (cell wall component) release when organisms killed (theoretical)
penetration of antibiotics into CSF is enhanced by (6)
high lipid solubility low molecular weight low degree of ionisation high serum concentration low degree of protein binding meningeal inflammation
3 main groups of CSF penetration
1 penetrate inflamed and non-inflamed meninges even at standard doses
e.g. metronidazole, trimethoprim, chloramphenicol (but bacteriostatic and resistance)
2 penetrate inflamed meninges or at high doses (tend to use)
e.g. benzylpenicillin, cephalosporin (3rd gen)
3 penetrate poorly
e.g. gentamicin, erythromycin, tetracycline
chloramphenicol use in meningitis
use with caution
reserve for allergic patients good penetration into CSF and brain tissue, IV and oral
bacteriostatic
resistance in Hib and pneumococci
rare= can get irreversible aplastic anaemia, grey baby syndrome
reserve agent for penicillin allergy, otherwise use other more effective treatment
what’s first line treatment in meningitis, benefits and drawback
ceftriaxone (main)/cefotaxime
activity against penicillin resistant pneumococci and ampicillin resistant Hib
good penetration
doesn’t cover listeria
benzylpenicillin in meningitis
no longer used empirically
4 hourly, high doses
lowers seizure threshold
reserved for sensitive strains
order benzylpenicillin, chloramphenicol and cefotaxime/ceftriaxone in order of highest penetration into BBB and lowest
chloramphenicol
cefotaxime/ceftriaxone
benzylpenicillin
choice of antibiotic depends on.. (5)
age clinical risks allergies gram film result local and national sensitivity data
empirical treatment in child<2 months
benzylpenicillin and gentamicin (cover e.coli), don’t have tight BBB, organisms exposed to in delivery or pregnancy through placenta
empirical treatment in child>2 months and adults
cefotaxime or ceftriaxone (and amoxicillin if >60 years or immunocompromised, to cover listeria)
treatment in meningococcus
benzylpenicillin if sensitive/ cefotaxime or ceftriaxone
treatment in pneumococcus
benzylpenicillin if sensitive/ cefotaxime or ceftriaxone
add vancomycin if risk of resistant stain (travel to high incidence countries)
treatment in hib (rare)
cefotaxime or ceftriaxone (chloramphenicol)
length of treatment
meningococcus= 7 days pneumococcus= 14 days hib= 7 days listeria= at least 21 days
meningitis and steroids
use steroids to dampen immune response
give prior to antibiotics for beneficial effect
risk of GI bleeding
reduces long term morbidity in children with hib meningitis (dexamethasone given)
prevention and control of meningitis
vaccines
chemoprophylaxis- reduce secondary cases in close contacts (rifampicin or ciprofloxacin)
presentation of brain abscess
focal neurological signs
raised intracranial pressure
headache
maybe fever
define abscess
a swollen area within body tissue, containing an accumulation of pus
define brain abscess
an abscess caused by inflammation and collection of infected material
routes of brain abscess (3)
1 direct spread via venous connections (ear and sinus infections)
2 haematogenous spread (complication of endocarditis)
3 direct implantation (trauma or surgery)
pathophysiology of brain abscess
- cerebritis with central inflammation
- ring of cerebritis (infection) surrounding a necrotic centre
- capsule formation (limits spread)
- can rupture, pus into CSF
drainage just as important as antibiotics
bacteria in brain abscess
usually streptococcus milleri
middle ear- usually enterobacteriaceae
staph skin organisms
where it comes from helps decide which bacteria it is
treatment of brain abscess
surgical and medical
s= drainage, excision via craniotomy
m= antibiotics
choice of antibiotic in abscess depends on (4)
1 site of abscess
2 predisposing factors
3 history of allergies
4 result of gram film and culture
antibiotic treatment of abscess by source
dental, sinus, haematogenous source= ceftriaxone and metronidazole, narrow down to benzylpenicillin and metronidazole if strep/anaerobic
otogenic source (ear)= ceftazidime, benzylpenicillin and metronidazole OR meropenem
post-operative/traumatic= vancomycin and meropenem
high dose for 6-8 weeks, 3 IV, 3-5 oral
