CNS Infections Flashcards
How is infection spread to the nervous system?
- a blood borne
• septicaemia, viraemia, infected blood cells, septic embolism (e.g. endocarditis, bronchiectasis, IV drug use) - direct spread
• adjacent infection, head injury etc - trauma (including iatrogenic - e.g. LP, ventriculo-peritoneal shunts)
- vertical transmission in pregnancy
- in all, important role for immunosuppression
What is meningitis and it’s usual cause?
• 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
What is pachymeningitis and it’s cause?
pachymeningitis = predominantly dural disease
• usually direct spread of infection from skull (otitis media, mastoiditis or fracture)
- can cause dural abscess
What are the types of infection under pachymeningitis?
- epidural infection
• suppuration between dura and skull or vertebral column - i.e. as abscess - 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
What is the most common bacteria that cause mengitis?
- neonates: coliforms, streptococci
- 2-5 years: haemophilus
- older children - adults: meningoccus, pneumococcus
- old age: pneumococcus
- in immunocompromised: pneumococcus, meningococcus, listeria
- TB and syphilis are also important causes
Describe the pathogenesis of meningitis?
• 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
Describe pneumococcal meningitis?
• commonest (lepto)meningitis in Malawi
• usually sporadic cases
• affects all ages
• and not just in AIDS
Describe meningococcal meningitis?
• 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)
Describe the pathology of bacterial meningitis?
- meningeal and superficial cortical vessels congested, often haemorrhagic: cord can be involved too
- infiltrate of neutrophils, so often obvious pus
- CSF often turbid - reduced glucose, increased cells (neutrophils) and increased protein
What are the complications of bacterial meningitis?
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
What causes cerebral abscesses?
- direct spread - sinuses or middle ear
- septic sinus thrombosis - spread of infection from mastoid or middle ear via sigmoid sinus
- blood spread, e.g. infective endocarditis, bronchiectasis etc - often multiple abscesses in parietal lobes
Describe cerebral abscesses?
- adjacent brain markedly oedematous
- abscesses frequently enlarge and become multiloculate
- presentation can be similar to meningitis, but often with focal signs, epilepsy and fever
- but also act/present as space-occupying lesion’s
Complications of cerebral abscesses include?
- meningitis
- focal neurological deficit
- epilepsy
- raised ICP, so herniation of the brain
Describe causes CNS tuberculosis?
- secondary to TB infection (75% are primary)
- meningitis (espec. in young) and /or abscesses (tuberculomas)
- 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
Describe causes of parasitic infections of the CNS?
taenia solium causing neurocystocercosis
• predeliction for CNS, causing cysts in brain parenchyma and/or subarachnoid space
Note: parasitic infections uncommon unless human parasites endemic
Describe toxoplasmosis of the CNS?
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
Describe cerebral malaria?
- epidemiology
- usually only seen in children under 10
- newcomers to falciparum malarial areas - Clinical presentation
- acute diffuse parenchymal disease
- accompanied by fever + / - meningitis - Motality
- rapidly fatal in ~ 25-50% - Micro pathology
- histological hallmark is sequestration of microcirculation by parasitised /non-parasitised red cells - Gross pathology
- causes ring-like lesions in brain
Describe other parasitic infections of the CNS?
- trypanosomaiasis
• chronic meningoencephalitis - entamoeba histolytica
• amoebic abscess - echinococcus granulosus
• hydatid cyst - toxocara canis
• eosinophilic meningitis with granulomas
Describe fungal infections of the nervous system?
• 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
Describe fetal CNS infections and their consequences?
- rubella
- deafness, blindness, microcephaly - CMV
- microcephaly - toxoplasma
- microcephaly - syphilis
- tertiary forms include GPI, tabes dorsalis and meningovascular syphilis - HIV
