Mirco- CNS Infections Flashcards
Pathogenesis
a) haematogenous spread – entry into the bloodstream, most common
b) direct implantation- open i.e. surgery
c) local extension – i.e. swimming
d) PNS into CNS
Meningitis - neuro damage causes
- Direct bacterial toxicity.
- Indirect inflammatory process and cytokine release and oedema.
- Shock, seizures, and cerebral hypoperfusion.
Mortality rate around 10%. In the UK, ~ 5% of meningitis survivors have neurological sequelae, mainly sensorineural deafness.
Meningitis - Classification
a) Acute - bacterial/pyogenic –> usually bacterial meningitis
b) Chronic – weeks of worsening headache, worsening fever and neck stiffness –> usually TB, spirochetes, cryptococcus
c) Aseptic –> usually acute viral meningitis
Acute Meningitis Causative Organisms
Neisseria meningitidis Streptococcus pneumoniae Haemophilus influenzae Listeria monocytogenes Group B Streptococcus Escherichia coli Mycobacterium tuberculosis Staphylococcus aureus Treponema pallidum Cryptococcus neoformans Candida Coccidioides immitis, Histoplasma capsulatum, Blastomyces dermatitidis
N.meningitidis
- Infectious cause of childhood death in all countries.
- Transmission is person-to-person, from asymptomatic carriers.
- Pathogenic strains are found in only 1% of carriers.
- Through nasopharyngeal mucosa in a susceptible individual.
- Cause infections in less than 10 days.
RASH:
- A nonblanching rash (petechial or purpuric) develops in 80% of children.
- A maculopapular rash remains in 13% of children, and no rash occurs in 7%.
MenB is a big one, on the immunisation schedule.
N.meningitidis - Meningitis vs Septicaemia
- 50% of cases have meningitis
- 7-10% have septicemia
- 40% have septicemia AND meningitis
The clinical difference is important as it guides management
Pathogenesis of meningococcal septicaemia
The clinical spectrum is produced by four processes:
1) Capillary leak- albumin and other plasma proteins leads to hypovolemia.
2) Coagulopathy- leads to bleeding and thrombosis.
- Endothelial injury results in platelet-release reactions
- The protein C pathway.
- Plasma anticoagulants.
(might stop you from doing an LP)
3) Metabolic derangement - particularly acidosis
4) Myocardial failure….multi-organ failure.
Amputation or skin grafting due to digital or limb ischemia is required in 2-5% of survivors.
Chronic Meningitis - TB
Incidence: 544 per 100,000 population in Africa.
More common in patients who are immunosuppressed.
Mortality was 5.5 deaths per 100,000 persons.
Involves the meninges and basal cisterns of the brain and spinal cord.
Can result in tuberculous granulomas, tuberculous abscesses (enhancing, thick walled), or cerebritis
Aseptic Meningitis
Aseptic meningitis is the most common infection of the CNS.
Patients with aseptic meningitis have headache, stiff neck, and photophobia.
A nonspecific rash can accompany these symptoms.
Eneteroviruses (e.g. Coxsackievirus group B and echoviruses) are responsible for 80-90% cases in which a causative organism of aseptic meningitis is identified. Herpes simplex also implicated.
It most frequently occurs in children younger than 1 year.
The clinical course of aseptic meningitis is self-limited and resolves in 1-2 weeks.
Encephalitis
Transmission is commonly either person to person, or through vectors: Mosquitoes, Lice, Ticks
Herpes is the most common cause of encephalitis in the UK –> medical emergency and needs treatment
Various viridae from Togavirus, Flavivirus, and Bunyavirus families.
But, West Nile Virus is becoming a leading cause of encephalitis internationally
Non-Viral Encephalitis - Causes
Bacterial encephalitis:
Listeria monocytogenes
Amoebic encephalitis:
- Naegleria fowleri
- Habitat – warm water
- Acanthamoeba species, and Balamuthia mandrillaris - brain abscess, aseptic or chronic meningitis
Toxoplasmosis encephalitis:
- An obligate intracellular protozoal parasite, Toxoplasma gondii.
- Via the oral, transplacental route or organ transplantation.
- Severe infection in immunocompromised patients.
- Affected organs include the gray and white matter of the brain, retinas, alveolar lining of the lungs, heart, and skeletal muscle.
Brain abscess - Pathohysiology and Microbiology
Pathophysiology:
- otitis media/mastoiditis/paranasal sinuses
- endocarditis/haematogenously
Microbiology: (mainly staph and strep) - Streptococci (both aerobic and anaerobic) - Staphylococci, - Gram-negative organisms. (particularly in neonates) - Mycobacterium tuberculosis - fungi - parasites - Actinomyces and Nocardia species
Spinal Infections
Pyogenic vertebral osteomyelitis common form of vertebral infection.
Direct open spinal trauma, from infections in adjacent structures, from hematogenous spread of bacteria to a vertebra.
Left untreated, it can lead to permanent neurologic deficits, significant spinal deformity, or death.
Spinal Infections - RFs
Advanced age Intravenous drug use Long-term systemic steroids Diabetes mellitus Organ transplantation Malnutrition Cancer
CSF Gram Stains - Pink Diplococci
Neg- menigiococcus
Rods
