CNS infection - meningitis and encephalitis Flashcards
Define meningitis
inflammation of the leptomeninges (the arachnoid and pia mater) and usually occurs due to a bacterial, viral, or fungal infection.
Most common cause of bacterial meningitis in the UK
Neisseria meningitidis and S pneumoniea - most common in adults is S. pneumoniae
Most commomn cause of viral meningitid
enterovirus
coxsackievirus
Common bacterial causes of MG?
- Group B strep,
- e coli
- s pneumoniea
- m tuberculosis
- Neisseria mengitidis
common fungal causes of mg
cryptococcus neoformans
candida albicans
Rf for mg
- Immunocompromised: numerous causes includingextremes of age(children and the elderly),infection(such as HIV) andmedication(such as chemotherapy)
- Non-immunised: at risk ofH. influenza, pneumococcal and meningococcal meningitis
- Crowded environment: students living in halls of residence are a commonly affected demographic
two methods of transmission for MG
Direct spread
Haematogenous
How does direct spread occur
- pathogen gets inside the skull or spinal column, and then penetrates the meninges ending up in the CSF
- sometimes the pathogen will come on open skin or through nose
how does haematogenous spread occur
Pathogen enters the bloodstream and moves through the endothelial cells in the blood vessels making up the blood-brain barrier and gets into the CSF.
What happens once a pathogen enters the CSF
- begins to multiply
- wbc release cytokines to recruit additional immune cells
- more than 5microlitres will suggest meningitid
what happens to glucose and protein levels in the csf
- glucose in csf falls to below 2/3 of the blood
- protein increases
Signs of meningitis
- Kernig’s sign: when the hip is flexed and the knee is at 90°, extension of the knee results in pain
- Brudzinski sign: severe neck stiffness causes the hips and knees to flex when the neck is flexed
- Petechial or purpuric non-blanching rash: associated with meningococcal disease (N. meningitidis)
- Pyrexia
- Reduced GCS
Symptoms of meningitis
- meningism - headache, photophobia, neck stiffness
- fever
- nausea and vomitting
- seizures
Investigations for MG
- fbc- leukocytosis
- CRP - raised inflammatory markers
- coagulation and blood glucose required for comparison
Lumbar puncture and CSF analysis
- CSF gram stain:S. pneumoniae(gram-positive cocci in chains);N. meningitidis(gram-negative diplococci)
- CSF culture
- CSF PCR:useful for viruses such as HSV and VZV
- CSF interpretation
