CSIM 1.80: Viral Infections of the CNS and Prions

Question 1

Infection

Answer 1

• From ganglia
  
  • From ears
  • From nasopharynx
  • Congenital meningeal defect
  • Bloodstream spread

Question 2

What are the viral causes of meningitis?

Answer 2

• Enteroviruses
  
  • Herpes simplex
  • Varicella Zoster
  • Mumps
  • HHV/HIV

Question 3

What are the potential complications of meningitis?

Answer 3

• Cerebral oedema (BACTERIAL)
  
  • Venous sinus thrombosis
  • Brain abscess
  • Septicaemia and DIC

Question 4

What are the types of mononuclear cells

What are the polymorphonuclear cells?

Answer 4

Mononuclear cells a.k.a. agranulocytes - characterised by the lack of granules in the cytoplasm and single lobed nuclei
• Lymphocytes
• Monocytes (macrophages, dendritic cells, foam cells)

Polymorphonuclear cells a.k.a. granulocytes - characterised by having granules in their cytoplasm
  •  Neutrophils
  •  Eosinophils
  •  Basophils
  •  Mast cells

Question 5

What are the monocytes

Answer 5

• Macrophages
  
  • Dendritic cells
  • Foam cells

Question 6

Describe what would be seen in the CSF of someone with a viral meningitis infection

Answer 6

• Clear/turbid
  
  • Mononuclear cells raised
  • Polymorph cells normal/absent
  • Protein slightly raised
  • Normal glucose

Question 7

Describe what would be seen in the CSF of someone with a bacterial pyogenic meningitis infection

Answer 7

• Turbid
  
  • Purulent (duh)
  • Mononuclear cells raised
  • Polymorph cells raised significantly
  • High protein
  • Low glucose

Question 8

Describe what would be seen in the CSF of someone with a tuberculosis meningitis infection

Answer 8

• Turbid
  
  • Viscous
  • Mononuclear cells raised significantly
  • Polymorph cells raised
  • High protein
  • Low glucose

Question 9

What are the symptoms of encephalitis

Answer 9

• Fever and headache
  
  • Seizures
  • Hallucinations, disorientation, confusion
  • Personality changes
  • Cranial nerve palsies
  • Focal neurological deficits

Question 10

What is the most common cause of encephalitis

Answer 10

Viruses

Question 11

What are the types of encephalitis?

Which viruses cause each?

Answer 11

Acute
• Commonest, due to acute infection
• All, apart from MMR

Subacute
• Years after initial infection
• Rubella

Post-infectious
• Post viral infection
• VZV, EBV, Mumps, Measles

Chronic
• Immunocompromised patients
• Enteroviruses

Question 12

How does HSV cause encephalitis?

Answer 12

By tracking back through the nerves to the trigeminal ganglion in the temporal region

Question 13

What are the most fatal and the most mild viral causes of encephalitis and meningitis?

Answer 13

Severe (encephalitis):
• Arbovirus
• HSV

Mild (usually only meningitis):
• Enteroviruses
• Mumps

Question 14

What imaging techniques can be used to investigate encephalitis?

Answer 14

CT & MRI:
• Shows oedema
• HSV visible in temporal lobes

EEG:
• HSV shows characteristic slow waves

Question 15

What is a transmissible spongiform encephalopathy?

Describe the incubation period for each

Answer 15

Progressive brain encephalopathies caused by PRIONS, which triggers the formation of amyloid plaques, which create holes in the cortex, causing it to be ‘spongy’ in appearance:
• Creutzfeldt-Jakob disease
• Gerstmann-Straussler-Scheinker syndrome
• Kuru

Symptoms similar to encephalitis, but can include myoclonic jerks (chorea, dystonia)

Question 16

What is the normal and infectious form of a prion-forming protein called?

Answer 16

Normal form:
PrPᶜ

Infective form:
PrPˢᶜ

(NB: C refers to ‘cellular’ PrP, while the Sc refers to ‘scrapie’, the prototypic prion disease, occurring in sheep)

Question 17

How do prions most commonly enter humans?

Answer 17

Through food:
• Bovine spongiform encephalopathy in cattle, due to cattle being fed meat-derived nutritional supplements with scrapie (from sheep)

Through blood transfusion from infected individuals