T9-L5: CNS Clinical Infections

Question 1

How can meningitis be classified?

Answer 1

• Acute pyogenic - usually bacterial
• Aseptic - usually viral or lymphocytic pleocytosis (and so non-infective) - blood cultures are therefore negative
• Chronic - the meningitis occurs over weeks and months. Causes include TB, spirochetes such as syphillis and Cryptococcus neoforman.

Question 2

What is the pathogenesis of meningitis?

Answer 2

1. Haematogenous spread - usual arterial route and is the most common.
2. Direct implantation e.g. after surgery (iatrogenic) or due to congenital causes (such as Meningomyelocele)
3. Local extension - often from the surrounding inter cranial structure e.g. teeth, mastoid and the sinuses
4. Along the peripheral nerves - usually due to viruses (HSV, rabies)

Question 3

What are the usual causes of meningitis?

Answer 3

1 month > - Streptococcus agalactiae, E. coli, Listeria monocytogenes

1 - 23 months - Streptococcus pnemonae, N. meningitidis, Streptococcus agalactiae, E.coli, H. influenzae

2 -50 years - Streptococcus pneumoniae, N. meningitidis

50 years > - Streptococcus pneumoniae, N. meningitidis, Listeria monocytogenese, aerobic gram negative bacilli

Question 4

What are the 3 features of meningism?

Answer 4

• Nuchal rigidity (neck stiffness)
• Photophobia (intolerance of bright light)
• Headache.

Question 5

What CSF abnormalities are seen in Meningitis?

Answer 5

Bacterial meningitis - CSF is cloudy and turbid. It also has a high level of polymorphs and high protein.

Aseptic meningitis - Clear CSF (slightly cloudy), high lymphocyte count

TB meningitis - Clear (slightly cloudy), raised lymphocytes, high protein and low glucose

Cryptococcal meningitis (fungal) - Clear CSF, raised lymphocytes, normal protein and normal glucose

Question 6

Who does viral meningitis usually infect and what virus cause it?

Answer 6

Usually effects children and young adults.

Aetiology:

• Enteroviruses: Echo, Coxsackie A, B
• Mumps and other paramyxoviruses
• HSV, VZV
• Adenovirues
• Others including HIV and arboviruses

Question 7

What is the biggest cause of encephalitis in the UK?

Answer 7

HSV particularly HSV1 and HSV2.

Other causes include:

• VZV, Cytomegalovirus, EBV, HSV6
• Adenovirus
• Influenza A
• Enteroviruses, poliovirus
• Measles, mumps, rubella - reduced incidince
• Rabies
• Adenoviruses

Question 8

What is the clinical presentation of encephalitis?

Answer 8

• Fever
• Headache
• Behavioural changes
• Altered states of consciousness
• Focal neurogenic deficits
• Seizures

Question 9

What is the urgent treatment of Herpes encephalitis?

Answer 9

Aciclovir

Question 10

What is neurosyphilis?

Answer 10

Neurosyphilis refers to infection of the central nervous system in a patient with syphilis. Neurosyphilis is a disease of the coverings of the brain, the brain itself, or the spinal cord. It can occur in people with syphilis, especially if they are left untreated.

Can lead to general paresis and tabes dorsals.

Question 11

What is the pathogenesis of brain abscess?

Answer 11

1. Usually contagious spreads from suppurative sources such as ear (40%), sinuses and teeth.
2. Haematogenous spread from distant focus e.g. endocarditis, bronchiectasis.
3. Trauma e.g. open cranial fracture, post-neurosurgery
4. Cryptogenic (no cause is recognised 15-20%)

Question 12

What is the aetiology of brain abscesses?

Answer 12

The bacteria responsible depend on the pathogenic mechanism involved. Brain abscesses are often mixed (polymicrobial)
• Streptococci (60-70 %) e.g. Streptococcus “milleri”
• Staphylococcus aureus (10-15%) most common pathogen in abscesses after trauma/surgery
• Anaerobes e.g. Bacteroides spp.
• Gram negative enteric bacteria (E.coli, Pseudomonas spp.)
• Others e.g. fungi, Mycobacterium tuberculosis, Toxoplasma gondii (where a new diagnosis of HIV is involved)

Question 13

Why do we drain brain abscesses (4)?

Answer 13

Drainage is treatment of choice (N.B small abscesses can be treated with antibiotics alone):
• To urgently reduce intracranial pressure
• To confirm diagnosis
• To obtain pus for microbiological investigation
• To enhance efficacy of antibiotics
To avoid spread of infection into the ventricles

Question 14

Why are different antibiotics needed to treat brain abscess compared to meningitis?

Answer 14

In Brian abscesses the blood brain barrier (BBB) is still in tact. Penetration of drugs into CSF and brain tissue differ. Ampicillin, Penicillin, Cefotaxime, Ceftazidime, and Metronidazole are able to cross the barrier and achieve therapeutic concentrations in intracranial pus

In meningitis we have a split breakdown of the BBB and so some of the drugs that would not usually penetrate may work.