CNS Infections: Meningitis, Encephalitis

Question 1

Important history questions

Answer 1

Locate the source of infection
Skull infection => CNS spread
-Otitis media
-Sinusitis
-Mastoiditis

Internal
-heart, lung, skin, abdo, pelvic

Via bloodstream more likely in IC
-HIV
-chemo
-immunosuppressed

Head trauma
-fracture, wounds

Surgery
-dental
-head
-valve, implants

Travel, vaccinations

Question 2

Key investigations

Answer 2

Blood culture

Head CT/MRI
CT body
Echo

Dental review

Question 3

Management

Answer 3

Urgent neurosurgical review
-ABx
-aspiration, drainage

Surgery needed if mass effect/neuro deficit

Question 4

General presentation of CNS infections

Answer 4

Headache - not relieved by simple analgesia
Fever
Seizure
N+V
Stiff neck
Visual changes

Mental state change
Focal neuro deficit

Question 5

Encephalitis
-pathophysiology
-presentation
-cause

Answer 5

Brain inflammation
-fever, headache
-reduced consciousness => coma
-seizure
-agitation
-focal neuro

Direct infection - mainly viruses
-HSV, VZV
-MMR
-rabies

AI

Question 6

Encephalitis
-investigations

Answer 6

GOLD STANDARD - CSF PCR
-identify cause

Blood, throat, stool, urine culture

Head CT - rule out other causes
EEG - lateralised periodic discharge in HSE

Question 7

Encephalitis
-management

Answer 7

Treat the underlying cause
HSE - aciclovir
HIV - HAART
JC - reverse immunosuppression

Question 8

HSE presentation

Answer 8

Typical encephalitis symptoms
-fever
-headache
-agitation
-seizures
-vomiting

Focal features - temporal lobe signs
-Wernicke’s aphasia
-prosopagnosia
-auditory agnosia
-sup hom quadrantopia
Cold sores

Question 9

Meningitis
-causes, pathogenesis

Answer 9

Bacterial, viral, protozoal, Non-infectious, AI

Contact with infected people/travel to endemic areas
-bacteria enter meninges => SA inflammation
Increased CSF outflow resistance => hydrocephalus, increased ICP => cerebral ischemia

Question 10

Meningitis
Most common causative organisms in
-U3 months - 3
-3months - 60 years - 2
-60+ - 3
-IC
-post surgery

In general
-in 20-40s

Answer 10

U3 months - Ecoli, GBS, listeria

3months - 60years - NMeningitidis, SPneumonia

60+ - +listeria
IC - listeria

Post surgery - S aureus, S epidermidis, G-ves

Most common causes in general - S pneumonia
20-40s => viral meningitis (ENTEROVIRUS)

Question 11

Meningitis
-classic triad
-presentation
-signs
-drawback of identifying these symptoms

Answer 11

Fever, confusion, neck stiffness

Headache
N+V
Non blanching rash
Photophobia, phonophobia
Fatigue, irritability

Meningeal irritation
-Kernig - unable to extend knee when hip flexed
-Brudzinski - knees, hip flexed when neck flexed

Cannot distinguish between viral and bacterial meningitis

Question 12

What are the CSF findings when healthy
- opening pressure
- appearance
- WCC
- differential count
- protein
- CSF/plasma glucose ratio

Answer 12

Opening pressure => 12-20
Appearance => clear
WCC CSF => <5
Differential count => N/A
CSF protein => < 0.4
CSF/plasma glucose => >0.66

Question 13

What are the CSF findings if you have bacterial meningitis
- opening pressure
- appearance
- WCC
- differential count
- protein (indicator of the no of inflammatory cells)
- CSF/plasma glucose ratio

Answer 13

Opening pressure => high
Appearance => turbid
WCC => raised (may be normal in early infection)
Differential count => neutrophils
Protein => raised (protein leak into fluid)
CSF/plasma glucose => v low (bacteria using glucose)

ALWAYS INTERPRET FINDINGS IN CLINICAL CONTEXT

Question 14

What are the CSF findings if you have viral meningitis
- opening pressure
- appearance
- WCC
- differential count
- protein
- CSF/plasma glucose ratio

Answer 14

Opening pressure => normal/high
Appearance => clear
WCC => raised
Differential count => lymphocytes
Protein => mildly raised
CSF/plasma glucose => normal
~~~

ALWAYS INTERPRET FINDINGS IN CLINICAL CONTEXT

Question 15

What are the CSF findings if you have TB/fungal meningitis
- opening pressure
- appearance
- WCC
- differential count
- protein
- CSF/plasma glucose ratio

Answer 15

Opening pressure => high
Appearance => clear/cloudy
WCC => raised
Differential count => lymphocytes
Protein => markedly raised
CSF/plasma glucose => v low

ALWAYS INTERPRET FINDINGS IN CLINICAL CONTEXT

Question 16

Meningitis
-diagnosis, investigations

Answer 16

Blood
-FBC, U&E, CRP, clotting, culture - organ function and sepsis
-meningococcal PCR
-glucose
-ABG

CT - if focal neurological deficits/specific underlying cause suspected
-identify ICP

GOLD STANDARD - LP CSF within 1hr
-if not possible within 1hr, give ABx after cultures taken
-CSF analysed for cell count, gram stain, glucose, protein, lactate, culture, bacterial/viral PCR
-analysed alongside blood glucose

LP should be delayed if
-sepsis/rapidly evolving rash
-resp/cardiac compromise
-significant bleed risk
-high ICP, focal neuro, papilledema, continuous/uncontrolled seizures, GCS U12

Question 17

Acute bacterial meningitis
Management in
-primary care
-secondary care
-management of viral
-prophylaxis of close contacts

Answer 17

IV/IM benzylpenicillin => admit to A&E

Supportive - fluids, nutrition, analgesia, antipyretics, antiemetics

Treat causative organism - EMPIRICALLY AS BACTERIAL UNTIL PROVEN OTHERWISE
-U3 months or 50+ - IV amox+cefotaxime
-3 months+ - IV cefotaxime

IV dexmeth if pneumococcal
Don’t give if
-U3months - affects neurodevelopment
-septic shock
-meningococcal
-IC
-post surgery

Viral - supportive only
-aciclovir if HSV encephalitis

Prophylaxis within 24hrs if close contact within 7 days before onset - cipro 1 dose

Question 18

What is the difference between purpura/petichiae in septicaemia and vasodilation of blood vessels

What do you need to consider in a patient with purpura/petichiae?

Answer 18

Purpura/petichiae => bleeding into skin, no blanching
Not specific to meningits, not always found in early disease

Vasodilation => compression of vessels => blanching

Question 19

Meningitis
What are the red flag signs and symptom in
-young children

Why is it important to identify these symptoms?

Answer 19

The younger the child, the less likely they are to present typically
-typical signs are often late due to greater physiological reserve

All ages => first specific clinical features = signs of sepsis

Cold, painful limbs
Pale, mottled skin
Rash (often a late sign)
Changes in HR, RR
Drowsy
Diarrhea
Thirst

Question 20

Why does meningococcal septicaemia kill/permanently damage survivors?
-complications?

Answer 20

Endotoxins => inflammatory response
Septic shock
-widespread VD
-myocardial damage

• intravascular coagulation => distal areas blocked, gangrenous, needs amputation
• vessel damage => petichiae, purpura

DISRUPTION OF NORMAL CV FUNCTIONING

Complications
- hearing loss
- seizures
- cognitive, motor, visual impairment
- hydrocephalus
- amputations

Question 21

What vaccines are currently being offered

Answer 21

MenB - part of baby vaccinations
ACWY - Year 9-10, advised for uni students

Question 22

Contraindications to CSF LP

Answer 22

High ICP
- reduced/fluctuating consciousness
- bradycardia
- HTN
- focal neuro signs
- abnormal posture, pupil reflexes
- papilloedema

Shock

Extensive/spreading purpura

Seizures
Coagulation abnormalities
- AC use
- thrombocytopenia

Question 23

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