CNS Infections

Question 1

How is infection spread to the nervous system?

Answer 1

1. a blood borne
   • septicaemia, viraemia, infected blood cells, septic embolism (e.g. endocarditis, bronchiectasis, IV drug use)
2. direct spread
   • adjacent infection, head injury etc
3. trauma (including iatrogenic - e.g. LP, ventriculo-peritoneal shunts)
4. vertical transmission in pregnancy
   - in all, important role for immunosuppression

Question 2

What is meningitis and it’s usual cause?

Answer 2

• usually means inflammation in subarachnoid space (arachnoid and pia mater)
- strictly speaking it’s leptomeningitis
- usually a blood borne infection though can be direct spread from the skull bones

Question 3

What is pachymeningitis and it’s cause?

Answer 3

pachymeningitis = predominantly dural disease
• usually direct spread of infection from skull (otitis media, mastoiditis or fracture)
- can cause dural abscess

Question 4

What are the types of infection under pachymeningitis?

Answer 4

1. epidural infection
   • suppuration between dura and skull or vertebral column - i.e. as abscess
2. subdural infection
   • abscess unusual
   • pus spreads in subdural space over hemispheres causing subdural empyema.
   • involvement of subdural vessels may cause thrombophlebitis and venous infarction of brain

Question 5

What is the most common bacteria that cause mengitis?

Answer 5

1. neonates: coliforms, streptococci
2. 2-5 years: haemophilus
3. older children - adults: meningoccus, pneumococcus
4. old age: pneumococcus
5. in immunocompromised: pneumococcus, meningococcus, listeria
6. TB and syphilis are also important causes

Question 6

Describe the pathogenesis of meningitis?

Answer 6

• incubation period ~ 4 days
• once in subarachnoid space, bacteria multiply
• pathogenetic effects follow release of agents inducing fever and acute inflammation (hyperaemia, exudation etc)
• inflammatory exudate can raise ICP and can reduce cerebral blood flow

Question 7

Describe pneumococcal meningitis?

Answer 7

• commonest (lepto)meningitis in Malawi
• usually sporadic cases
• affects all ages
• and not just in AIDS

Question 8

Describe meningococcal meningitis?

Answer 8

• commonest variety worldwide, but less so in Malawi
• epidemics in small communities
• spread = droplet spread from asymptomatic nasal carriers
• petechial rash can herald DIC with potentially lethal adrenal hemorrhage (Waterhouse-Friederichsen syndrome)

Question 9

Describe the pathology of bacterial meningitis?

Answer 9

1. meningeal and superficial cortical vessels congested, often haemorrhagic: cord can be involved too
2. infiltrate of neutrophils, so often obvious pus
3. CSF often turbid - reduced glucose, increased cells (neutrophils) and increased protein

Question 10

What are the complications of bacterial meningitis?

Answer 10

Complications (~ 25% die) include -
1. cerebral abscess
2. subdural empyema
3. cerebral infarction
4. obstructive hydrocephalus
5. epilepsy
6. cranial nerve palsies (VI & VIII)
7. and DIC if meningococcal

Question 11

What causes cerebral abscesses?

Answer 11

1. direct spread - sinuses or middle ear
2. septic sinus thrombosis - spread of infection from mastoid or middle ear via sigmoid sinus
3. blood spread, e.g. infective endocarditis, bronchiectasis etc - often multiple abscesses in parietal lobes

Question 12

Describe cerebral abscesses?

Answer 12

1. adjacent brain markedly oedematous
2. abscesses frequently enlarge and become multiloculate
3. presentation can be similar to meningitis, but often with focal signs, epilepsy and fever
4. but also act/present as space-occupying lesion’s

Question 13

Complications of cerebral abscesses include?

Answer 13

1. meningitis
2. focal neurological deficit
3. epilepsy
4. raised ICP, so herniation of the brain

Question 14

Describe causes CNS tuberculosis?

Answer 14

1. secondary to TB infection (75% are primary)
2. meningitis (espec. in young) and /or abscesses (tuberculomas)
3. meningitis from rupture of subependymal tubercles
   > rarely from direct spread from vertebral body
   > causes subacute meningitis with occasional isolated cranial nerve palsies
   > but can be non-specific and diagnosed only after LP
   Note: tuberculomas present like other cerebral abscesses

Question 15

Describe causes of parasitic infections of the CNS?

Answer 15

taenia solium causing neurocystocercosis
• predeliction for CNS, causing cysts in brain parenchyma and/or subarachnoid space
Note: parasitic infections uncommon unless human parasites endemic

Question 16

Describe toxoplasmosis of the CNS?

Answer 16

Toxoplasma gondii
• most frequent cause of focal CNS disease in AIDS
~ 50% patients in Africa and Europe
• often constitutional symptoms/signs at first, but then more obviously neurological ones, sometimes with localising signs
• ICP may be raised with coma/death if untreated

Question 17

Describe cerebral malaria?

Answer 17

1. epidemiology
   - usually only seen in children under 10
   - newcomers to falciparum malarial areas
2. Clinical presentation
   - acute diffuse parenchymal disease
   - accompanied by fever + / - meningitis
3. Motality
   - rapidly fatal in ~ 25-50%
4. Micro pathology
   - histological hallmark is sequestration of microcirculation by parasitised /non-parasitised red cells
5. Gross pathology
   - causes ring-like lesions in brain

Question 18

Describe other parasitic infections of the CNS?

Answer 18

1. trypanosomaiasis
   • chronic meningoencephalitis
2. entamoeba histolytica
   • amoebic abscess
3. echinococcus granulosus
   • hydatid cyst
4. toxocara canis
   • eosinophilic meningitis with granulomas

Question 19

Describe fungal infections of the nervous system?

Answer 19

• more common in immunosuppression
• usually blood spread from lungs, but also direct
1. cryptococcus
• usually causes meningitis
2. candida and aspergillus
• usually cause abscesses
3. mucormycosis
• usually uncontrolled diabetics - granulomatous nasal infection spreading to brain

Question 20

Describe fetal CNS infections and their consequences?

Answer 20

1. rubella
   - deafness, blindness, microcephaly
2. CMV
   - microcephaly
3. toxoplasma
   - microcephaly
4. syphilis
   - tertiary forms include GPI, tabes dorsalis and meningovascular syphilis
5. HIV