25 - Viral Meningitis/Encephalitis Flashcards
Aseptic meningitis - clinical picture
White cell count >5x10^6 per litre in CSF
Negative bacterial culture of CSF
Viruses most common cause
Virus info
Basic infectious particle = virion
Simple virus structure
Nucleic acid with capsid maybe w/ lipid envelope/ other proteins or enzymes
Aetiology of meningitis
Enteroviruses (leading cause) Herpes viruses Arboviruses Mumps Virus HIV Adenovirus Measles Influenza Parainfluenza type 3 Lymphocytic choriomeningitis virus (LCMV)
Types of enteroviruses
Echoviruses Coxsackie virus Parecho virus Enterovirus (70&71) Polio virus
Types of herpes viruses
HSV VZV (varicella zoster) CMV Epstein Barr Virus (EBV) HHV6, HHV7
Pathogenesis of meningitis
Colonisation of mucosal surfaces Invasion of epithelial surface Replication in cells Dissemination and CNS invasion Symptoms mainly due to inflammatory response in the CNS
How does it invade the CNS
Via cerebral microvascular endothelial cells
Via choroid plexus epithelium
Spread along the olfactory nerve
Meningitis - clinical presentation
Fever
Meningism - headache, neck stiffness, photophobia
Sometimes viral prodome (lethargy, myalgias, arthralgias, sore throat, D&V, rash)
Meningitis - clinical presentation in children
Neonates - signs might be absent
Look for nuchal rigidity (neck stiffness)
Bulging anterior fontanelle
Meningitis - examinations
Kernig’s sign
Brudzinski’s sign
Nuchal rigidity
Kernig’s sign
Hip and knee flexed to 90 degrees, the knee cannot be extended due to pain/stiffness in the hamstrings
Brudzinski’s sign
Flexing the neck causes the hips and knees to flex
Nuchal rigidity
Resistance to flexion of the neck
Meningitis - investigations
Blood tests - FBC, U&E, CRP, clotting + blood culture
CT head
Lumbar puncture - should be within an hour
Meningitis - what would CTing head see?
Raised intra-cranial pressure
e.g. mass lesion, subarachnoid haemorrhage
Meningitis - lumbar puncture (LP) - why?
Microscopy, culture, sensitivity (MC&S)
Protein
Glucose (MUST CHECK GLUCOSE AT SAME TIME)
Viral PCR: enteroviruses, HSV, VZV
CSF findings in viral meningitis
White cell count: lymphocytic mildly elevated
Glucose (ratio CSF:plasma) normal is around 50% - viral it ranges from normal to slightly low
Bacterial vs viral meningitis
Higher opening pressure in bac Higher WBC count WBC differential = >80% PMN More protein Both around 40% glucose of serum
What other microbiology investigations could you get?
Throat swab/stool sample for entervirus PCR
Serology - mumps, EBV,CMV,HIV, other travel-related
Treatments and outcome
Start approprite IV antibiotics if risk of bacterial meningitis
No specific treatment for viral (could use aciclovir)
Mainly supportive therapy (analgesia and antipyretics)
Good prognosis
NOTIFIABLE DISEASE FOR PHE
Enteroviral meningitis - symptoms, treatments, prognosis
Commonest cause Late summer/autumn epidemics Fever, vomiting, anorexia, rash, URT No specific treatment Full recovery normal
HSV
2 forms - 1&2
HSV 2 is 2nd commonest cause of viral meningitis
Mollaret’s meningitis - recurrent aseptic meningitis but major cause = HSV2
HSV1
Causes cold sores and viral encephalitis
HSV2
Causes genital herpes and meningitis
VZV
Primary = chickenpox (varicella)
Secondary = shingles (zoster)
No evidence aciclovir is beneficial
Complete normal recovery
Mumps
10-30% are mumps cases CNS symptoms 5 days after onset of parotitis Features: ab pain, orchitis No specific treatment Full recovery normal Preventable w/ vaccination
Viral encephalitis - aetiology
HSV - 90% are HSV1 EBV Measles Mumps Enteroviruses inc. polio Bacteria - strep pneumoniae, neisseria meningitidis, TB Acute disseminated encephalomyopathy (ADEM) Unknown = 37%
Viral encephalitis - clinical presentation
Altered mental state is key - low GCS
Fever
Headache
Meningism
Focal neurology: seizures, weakness, dysphasia, cranial nerve palsy, ataxia
Viral encephalitis - investigations
Bloods tests- FBC, U&E, CRP, clotting & blood cultures
Serology
CT - necessary before LP
MRI - may see changes typical of HSV encephalitis
LP - microscopy, culture and sensitivity, protein/glucose, viral PCR
EEG - 75% will show abnormal temporal lobe activity
CSF findings are different or same comparing viral encephalitis with meningitis?
Same
Viral encephalitis - treatment
High dose IV aciclovir for 14-21 days
Start on clinical suspicion do not wait for CSF results
Oral switch not recommended
Herpes simplex encephalitis
Rare, but mortality high in untreated
MRI shows clearer signs
Bimodal distribution, 50 yo
Equally spread in gender
HSE pathogenesis
Primary infection vs reactivation - direct transmission of the virus along neural/olfactory pathways vs reactivation in the trigeminal ganglia
Acute focal necrotising encephalitis
Inflammation / swelling of brain tissue
Viral encephalitis - outcome
Mortality untreated - 70%
Mortality is treated is high - 28% at 18months
If GCS
Acute disseminated encephalomyelopathy (ADEM)
immune-mediated CNS demyelination Can follow viral illness or vaccination Clinical features same as encephalitis CSF findings = viral meningitis MRI helpful Treatment is steroids/other immunosuppressants Recovery variable
Take home messages
Viral meningitis often indistinguishable from bacterial - need LP
LP essential for diagnosis of both meningitis & encephalitis
Always take concurrent serum glucose sample when do LP
HSE is medical emergency needs IV aciclovir
