CNS infections

Question 1

Main routes of CNS infection

Answer 1

• Blood borne - most common
• Parameningeal suppuration from e.g. sinusitis
• Direct through dura deficits e.g. trauma
• Cribiform plate

Question 2

Inflammatory process of bacterial meningitis

Answer 2

• Endotoxins of gram negative and peptidoglycan components of gram positive bacterial cell walls act as inflammatory mediators; TNF, IL-1, IL-6, IL-8 etc
• Neutrophils migrate to CNS and release protelytic products and toxic O radicals; CSF pressure increases due to capillary infiltration
• Damage to vascular epithelium alters permeability of BBB; allows effector cells to enter

Question 3

Symptoms of bacterial meningitis

Answer 3

• Meningeism
  
  • Headache, stiff neck and back, Kerning’s sign
• Fever
• Rash
• Impaired consciousness
• Seizures

Question 4

Specific symptoms for bacterial meningitis in children

Answer 4

Typical signs absent if <18 months. May be flaccid, have strange crym convulsions, and bulging fontanelle

Vomiting and fever often only sign

Question 5

Main organisms causing bacterial meningitis

Answer 5

• Neisseria meningiditis = children/young adults
• Strep. pneumonia = young children/elderly
  
  • Alcohol abuse, diabetes
• Hib - vaccinated against
• Group B strep = babies, by vagianl delivery
• E.coli= noenates
• Listeria monocytogenes

Question 6

Management of bacterial menigitis

Answer 6

• Ceftriaxone (benzylpenicillin if sensitive) in most cases

If unknown:

• Over 2 months: Ceftriaxone and amoxicillin
• Under 2 months: Benzylpenicillin and gentamicin

Question 7

Main causes of viral meningitis

Answer 7

• Enteroviruses - coxsachie or echoviruses
• Herpes virus - Herpes simplex and varicella zoster
• Mumps - MMR vaccien prevents
• Flavivirus
• HIV

Question 8

Organisms causing encephalitits

Answer 8

= Inflammation of brain

• Herpes Simplex - treat with IV acyclovir
• Enteroviruses
• Listeria
• Measles and mups

Post infection:

• Chickenpox
• Flu A and B
• Measles

Question 9

Clinical features of myelitits

Answer 9

=Inflammation of the spinal cord

• transverse - acute transection of cord
• ascending
• Anterior horn cells

Question 10

Features of encephelomyelitis

Answer 10

= A combination of encephalitits and myelitis

Commonest route of entry to CNS is blood.

Polio and Rabies enter via peripheral nerves

Viral causes: HSV, measles, mumps, polio, west nile

Arbovirus via mosquito vector