CNS Infections Flashcards
What are the causes of meningitis?
viruses, bacteria, other infectious causes and other non infectious causes
What is aseptic meningitis?
meningitis that is culture negative - either because it is non bacterial or the bacteria cannot be cultured
What are the usual aetiological agents of viral meningitis?
enteroviruses
Does viral meningitis require treatment?
no - it is usually self limiting
What are the 3 bacteria that are the commonest cause of bacterial meningitis?
strep pneumoniae, h. influenzae and neisseria meningitidis
What feature of the bacteria mean that they cause meningitis?
they evade the immune system because they are encapsulated and so can’t be fixed by complement and can’t be phagocytosed
Describe the pathogenesis of meningitis
Commensals invade the bloodstream where they multiply if they survive the host immune responses, they then cross the blood brain barrier and invade the meninges and CNS. Due to the immune response there is increased permeability of the blood brain barrier and an increase in ICP. Then the host immune response causes neurotoxic damage and neuronal injury.
What are the clinical features of meningitis in adults?
fever, vomiting, headaches, stiff neck, altered mental state, photophobia, headache and seizure
What are the clinical features of meningitis in children?
fever, nausea, vomiting, irritability, bulging fontanelle
What is the distinctive clinical feature of meningococcaemia?
purpuric rash
How is meningitis defined clinically?
by an abnormal CSF
What is the normal pressure of the CSF?
150mm
What is the normal white cell count of the CSF?
less than 5 X 10^6
What is the normal red cell count of the CSF?
0
What is the normal protein in the CSF?
less than 0.4g/L
What is the normal glucose in the CSF?
60% of the blood level
What is the normal appearance of CSF?
clear
What are the CSF results for viral meningitis?
slightly increased white cells and protein but otherwise normal
What are the CSF results for bacterial meningitis?
increased pressure, cloudy, very high white cell count, gram stain positive, high protein count, low glucose
What are the CSF results for TB meningitis?
increased pressure, cloudy, increased white cells, very high protein, very low glucose
When is a lumbar puncture contraindicated?
raised ICP, shock, extensive purpuric rash, convulsions, coagulation abnormalitites, infection at lumbar puncture site, respiratory insufficiency
Why does a CSF sample need to be sent to the lab immediately?
if left the cells will lyse and the cell count will rapidly decrease
Do CSF test results definitively distinguish between different types of meningitis?
no - wide variety of results
What is the treatment for bacterial meningitis?
resuscitation/life support, fluids, antibiotics, steroids
What antibiotics are given for bacterial meningitis?
cephalosporin with additional gentamicin and penicillin if under 3 months
What is encephalitis?
inflammation of the brain
What is the most common cause of encephalitis?
HSV
What is the treatment for encephalitis?
aciclovir
How can you distinguish between meningitis and encephalitis clinically?
encephalitis involves an altered conscious state
What is menigoencephalitis?
a combination of meningitis and encephalitis
What vaccines are available for meningitis?
Hib, meningococcus C and B, pneumococcus
