25 - Viral Meningitis/Encephalitis

Question 1

Aseptic meningitis - clinical picture

Answer 1

White cell count >5x10^6 per litre in CSF
Negative bacterial culture of CSF
Viruses most common cause

Question 2

Virus info

Answer 2

Basic infectious particle = virion
Simple virus structure
Nucleic acid with capsid maybe w/ lipid envelope/ other proteins or enzymes

Question 3

Aetiology of meningitis

Answer 3

Enteroviruses (leading cause)
Herpes viruses
Arboviruses
Mumps Virus
HIV
Adenovirus
Measles
Influenza
Parainfluenza type 3
Lymphocytic choriomeningitis virus (LCMV)

Question 4

Types of enteroviruses

Answer 4

Echoviruses
Coxsackie virus
Parecho virus
Enterovirus (70&71)
Polio virus

Question 5

Types of herpes viruses

Answer 5

HSV
VZV (varicella zoster)
CMV
Epstein Barr Virus (EBV)
HHV6, HHV7

Question 6

Pathogenesis of meningitis

Answer 6

Colonisation of mucosal surfaces
Invasion of epithelial surface
Replication in cells
Dissemination and CNS invasion
Symptoms mainly due to inflammatory response in the CNS

Question 7

How does it invade the CNS

Answer 7

Via cerebral microvascular endothelial cells
Via choroid plexus epithelium
Spread along the olfactory nerve

Question 8

Meningitis - clinical presentation

Answer 8

Fever
Meningism - headache, neck stiffness, photophobia
Sometimes viral prodome (lethargy, myalgias, arthralgias, sore throat, D&V, rash)

Question 9

Meningitis - clinical presentation in children

Answer 9

Neonates - signs might be absent
Look for nuchal rigidity (neck stiffness)
Bulging anterior fontanelle

Question 10

Meningitis - examinations

Answer 10

Kernig’s sign
Brudzinski’s sign
Nuchal rigidity

Question 11

Kernig’s sign

Answer 11

Hip and knee flexed to 90 degrees, the knee cannot be extended due to pain/stiffness in the hamstrings

Question 12

Brudzinski’s sign

Answer 12

Flexing the neck causes the hips and knees to flex

Question 13

Nuchal rigidity

Answer 13

Resistance to flexion of the neck

Question 14

Meningitis - investigations

Answer 14

Blood tests - FBC, U&E, CRP, clotting + blood culture
CT head
Lumbar puncture - should be within an hour

Question 15

Meningitis - what would CTing head see?

Answer 15

Raised intra-cranial pressure

e.g. mass lesion, subarachnoid haemorrhage

Question 16

Meningitis - lumbar puncture (LP) - why?

Answer 16

Microscopy, culture, sensitivity (MC&S)
Protein
Glucose (MUST CHECK GLUCOSE AT SAME TIME)
Viral PCR: enteroviruses, HSV, VZV

Question 17

CSF findings in viral meningitis

Answer 17

White cell count: lymphocytic mildly elevated

Glucose (ratio CSF:plasma) normal is around 50% - viral it ranges from normal to slightly low

Question 18

Bacterial vs viral meningitis

Answer 18

Higher opening pressure in bac
Higher WBC count
WBC differential = >80% PMN
More protein
Both around 40% glucose of serum

Question 19

What other microbiology investigations could you get?

Answer 19

Throat swab/stool sample for entervirus PCR

Serology - mumps, EBV,CMV,HIV, other travel-related

Question 20

Treatments and outcome

Answer 20

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

Question 21

Enteroviral meningitis - symptoms, treatments, prognosis

Answer 21

Commonest cause
Late summer/autumn epidemics
Fever, vomiting, anorexia, rash, URT
No specific treatment 
Full recovery normal

Question 22

HSV

Answer 22

2 forms - 1&2
HSV 2 is 2nd commonest cause of viral meningitis
Mollaret’s meningitis - recurrent aseptic meningitis but major cause = HSV2

Question 23

HSV1

Answer 23

Causes cold sores and viral encephalitis

Question 24

HSV2

Answer 24

Causes genital herpes and meningitis

Question 25

VZV

Answer 25

Primary = chickenpox (varicella) Secondary = shingles (zoster) No evidence aciclovir is beneficial Complete normal recovery

Question 26

Mumps

Answer 26

``` 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 ```

Question 27

Viral encephalitis - aetiology

Answer 27

``` HSV - 90% are HSV1 EBV Measles Mumps Enteroviruses inc. polio Bacteria - strep pneumoniae, neisseria meningitidis, TB Acute disseminated encephalomyopathy (ADEM) Unknown = 37% ```

Question 28

Viral encephalitis - clinical presentation

Answer 28

Altered mental state is key - low GCS Fever Headache Meningism Focal neurology: seizures, weakness, dysphasia, cranial nerve palsy, ataxia

Question 29

Viral encephalitis - investigations

Answer 29

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

Question 30

CSF findings are different or same comparing viral encephalitis with meningitis?

Answer 30

Same

Question 31

Viral encephalitis - treatment

Answer 31

High dose IV aciclovir for 14-21 days Start on clinical suspicion do not wait for CSF results Oral switch not recommended

Question 32

Herpes simplex encephalitis

Answer 32

Rare, but mortality high in untreated MRI shows clearer signs Bimodal distribution, 50 yo Equally spread in gender

Question 33

HSE pathogenesis

Answer 33

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

Question 34

Viral encephalitis - outcome

Answer 34

Mortality untreated - 70% Mortality is treated is high - 28% at 18months If GCS

Question 35

Acute disseminated encephalomyelopathy (ADEM)

Answer 35

``` 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 ```

Question 36

Take home messages

Answer 36

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