Viral meningitis/encephalitis Flashcards
What is encephalitis?
Inflammation of the brain parenchyma - grey and white matter
What is meningo-encephalitis?
Inflammation of the brain and meninges
Are encephalitis and meningitis easily distinguishable clinically?
No
What is meant by aseptic meningitis?
1) Clinical picture of meningitis
2) White cell count above normal in CSF (>5x10^6/L)
3) Negative bacterial culture of the CSF
What are the most common cause of aseptic meningitis?
Viruses
Other than viruses name 7 other causes of aseptic meningitis?
1) Partially treated bacterial meningitis
2) Listeria
3) TB
4) Syphilis
5) Malignancy
6) Autoimmune conditions
7) Drugs
What is a virion
basic infectious particle
What is the simple structure of a virus?
1) Nucleic acid - may be DNA or RNA and single or double stranded with multiple or just one strand - linear or circular
2) Capsid - protein coat made up of capsomeres (subunits)
Other than the simple virus structure what other 2 things can some viruses contain?
1) Some have a lipid envelope (derived from host cell membrane as they bud off)
2) Some contain other proteins / enzymes
Give 3 possible functions of the enzymes found in some viruses?
1) Replicating genetic material
2) Influencing transcription (by host material)
3) Protein modification
In which group is viral meningitis most common, what are the 2 peaks of hospital admission?
Neonates and children
Peaks in:
1) Neonates
2) Aged ~5years
What is the incidence of viral meningitis per 100,000?
5-15 cases per 100,000
What kind of viruses are the leading cause of viral meningitis, give 5 examples of that kind?
Enteroviruses
1) Echoviruses
2) Coxsackie virus
3) Parecho viruses
4) Enteroviruses 70 and 71
5) Poliovirus
Other than enteroviruses what other group of viruses commonly cause viral meningitis?
Herpes viruses
Give 5 examples of herpes viruses which commonly cause viral meningitis?
1) Herpes simplex virus 2
2) Varicella zoster virus
3) Cytomegalovirus
4) HHV6, HHV7
5) Epstein barr virus
Does HSV1 or 2 more commonly cause viral meningitis?
HSV2
What is the name of the Japanese encephalitis virus?
Arboviruses
Other than enteroviruses and herpes viruses which 7 other viruses cause viral meningitis?
1) Mumps Virus
2) HIV
3) Adenovirus
4) Measles
5) Influenza
6) Parainfluenza type 3
7) Lymphocytic choriomeningitis virus (LCMV)
In what percentage of cases of viral meningitis is the cause unknown?
35%
What are the symptoms mainly attributable to in viral meningitis?
Bodies reaction to the virus - the inflammatory response in the CNS
What are the 4 steps in the pathogenesis of viral meningitis?
1) Colonisation of mucosal surfaces
2) Invasion of epithelial surface
3) Replication in cells
4) Dissemination and CNS invasion
What are the 3 modes of CNS invasion for viral causes of meningitis?
1) Via cerebral microvascular endothelial cells
2) Via choroid plexus epithelium
3) Spread along the olfactory nerve
What 3 symptoms make up meningism?
1) Headache
2) Neck stiffness
3) Photophobia
What are the 3 main features of a clinical presentation of viral meningitis?
1) Fever
2) Meningism (headache, neck stiffness, photophobia)
3) Sometimes viral prodrome (lethargy, myalgia, arthralgias, sore throat, D&V, rash)
What 6 features can be seen in a viral prodrome?
1) Lethargy
2) Myalgia
3) Arthralgia
4) Sore throat
5) D&V
6) Rash
How may the clinical presentation of viral meningitis differ in neonates/infants?
1) Meningeal signs may be absent
2) Look for nuchal rigidity (neck stiffness)
3) May see a bulging anterior fontanelle (from raised ICP)
What is Kernig’s sign (found on examination for meningitis)?
With hip and knee flexed at 90 degrees, the knee cannot be extended due to pain/stiffness in the hamstrings
What is Brudzinski’s sign (found on examination for meningitis)?
Flexing the neck causes the hips and knees to flex
What is nuchal rigidity?
Resistance to flexion of the neck
What blood tests would be carried out when investigating meningitis? 6
1) FBC
2) U&E
3) CRP
4) Clotting (need to know OK if going to do a LP)
5) Blood culture
6) Blood glucose (to compare to CSF glucose)
Why would a CT head be carried out in investigating viral meningitis?
To look for evidence of raised ICP (important to know if going to do a LP - and is therefore indicated before an LP in certain circumstances) and alternative diagnosis
What is the first investigation which should be carried out ideally?
Lumbar puncture
For what 4 reasons would a lumbar puncture be carried out in suspected viral meningitis?
1) Microscopy, culture and sensitivity (MC&S)
2) Protein
3) Glucose (must check blood glucose at the same time)
4) Viral PCR: enteroviruses, HSV, VZV