MI: CNS Infections and Meningitis

Question 1

What are the routes of entry into the CNS?

Answer 1

• Haematogenous
• Direct implantation
• Local extension
• PNS into CNS (rabies)

Question 2

What is the most common route of entry for pathogens?

Answer 2

Haematogenous

Question 3

What is aseptic meningitis?

Answer 3

Meningitis that is caused by viruses and is not purulent

Question 4

What are the causes of neurological damage in meningitis

Answer 4

• Direct bacterial toxicity
• Indirect inflammatory response, cytokine release and oedema
• Shock, seizures and cerebral hypoperfusion

Question 5

What are the three types of meningitis?

Answer 5

• Acute (hours to days) - bacterial
• Chronic (days to weeks) - TB and weird
• Aseptic (caused by viruses so there is no pus)

Question 6

Name three organisms that cause acute meningitis.

Answer 6

• Neisseria meningitidis
• Streptococcus pneumoniae
• Haemophilus influenzae

Question 7

How many serotypes of N. meningitidis are there?

Answer 7

N. meningitidis can be classified into 12 serogroups based on its capsular polysaccharide; serogroups A, B, C, W, X, and Y are the primary causes of meningococcal disease worldwide

Question 8

List some other, rarer bacterial causes of acute meningitis.

Answer 8

• Listeria monocytogenes
• Group B Streptococcus
• Escherichia coli

Question 9

How does N. meningitidis enter the body?

Answer 9

Through the nasopharyngeal mucosa in susceptible individuals

NOTE: only 1% of carriers of N. meningitidis have pathogenic strains

Question 10

How long does N. meningitidis take to cause infection?

Answer 10

< 10 days

Question 11

What are the four processess that occur in septicaemia?

Answer 11

• Capillary leak - albumin and other plasma proteins lead to hypovolaemia
• Coagulopathy - leads to bleeding and thrombosis, endothelial injury results in platelet release reactions, the protein C pathway and plasma anticoagulants are affected
• Metabolic derangement - particularly acidosis
• Myocardial failure - and multi-organ failure

This is why you dont do lumbar pucture - they’ll bleed out

Question 12

Outline the presentation of TB meningitis.

Answer 12

• Similar presentation to bacterial meningitis but much longer to present (weeks instead of days)
• More likely to involve brain and cause neurological changes
• Tends to occur in immunocompromised patients
• No rash

Question 13

List some complications of TB meningitis.

Answer 13

• Tuberculous granulomas
• Tuberculous abscesses
• Cerebritis

Question 14

What is a typical MRI feature of TB meningitis?

Answer 14

Leptomeningeal enhancement
(arachnoid and pia mater appear brighter)

Question 15

What is the most common infections of the CNS?

Answer 15

Aseptic meningitis (aseptic = negative CSF bacterial cultures)

Question 16

What are the most common causative organisms in aseptic meningitis?

Answer 16

Enteroviruses:

• Coxsackie group B viruses
• Echoviruses

Question 17

Which age group is susceptible to aseptic meningitis?

Answer 17

< 1 year

NOTE: normally self-resolving after 1-2 weeks

Question 18

List some viruses that cause encephalitis.

Answer 18

• Herpes simplex virus (MOST COMMON)
• Mumps
• Measles
• Enteroviruses

Question 19

What is the first line investigation for encephalitis?

Answer 19

1st line: CT Head (to exclude other pathologies and raised ICP) -> LP to identify cause (if no pathology foundMRI is gold standard -> gyral oedema)

Question 20

What is becoming a leading cause of encephalitis worldwide?

Answer 20

West Nile virus

NOTE: this is transmitted by mosquitoes and birds

Question 21

How is West nile in the UK

Answer 21

Infects birds
Birds migrate
Affects southern europe
people go on holiday

Question 22

Which bacterium is associated with causing encephalitis?

Answer 22

Listeria monocytogenes

Question 23

Name two types of amoeba that cause encephalitis.

Answer 23

• Naegleria fowleri
• Acanthamoeba species and Balamuthia mandrillaris

NOTE: these amoebae spread by direct extension (e.g. through the cribiform plates)
up your nose - swimming in the baths of bath
still, stagnant water

Question 24

What is toxoplasmosis and how is it spread?

Answer 24

• Obligate intracellular parasite
• Spread via oral, transplacental or organ transplant route

Question 25

How do bacteria that cause brain abscesses tend to spread?

Answer 25

Direct extension (e.g. from otitis media, mastoiditis or paranasal sinuses)

Question 26

List some organisms that can cause brain abscesses.

Answer 26

* *Staphylococci* * *Streptococci* * Gram-negative organisms (mainly in neonates) * TB * *Actinomyces* and *Nocardia* species

Question 27

Name a common spinal infection.

Answer 27

Pyogenic vertebral osteomyelitis

Question 28

How can pyogenic vertebral osteomyelitis spread?

Answer 28

Direct open spinal trauma from infections in adjacent structures

Question 29

What are some long-term consequences of pyogenic vertebral osteomyelitis?

Answer 29

* Permanent neurologic defects * Significant spinal deformity * Death

Question 30

List some risk factors for pyogenic vertebral osteomyelitis.

Answer 30

* Age * IVDU - **staph aureus** * Long-term systemic steroids * Diabetes mellitus * Organ transplantation * Cancer * Malnutrition

Question 31

Compare the use of MRI and CT in CNS infections.

Answer 31

MRI is better than CT at detecting parenchymal abnormalities such as abscesses and infarctions ## Footnote CT can be useful for looking at raised ICP

Question 32

List some other useful tests for suspected meningitis.

Answer 32

* Blood culture - typical * Blood PCR - aseptic * Throat swab - Meningococus, Strep. Pneumo ## Footnote Strep Pneumo (1in5) and Meningococcus (1in20) carried in nasopharynx

Question 33

What studies can be done with CSF?

Answer 33

* Colour/clarity * Cell counts * Chemistry (protein and glucose) * Stains (Gram, auramine, Inda Ink etc.) * Cultures * PCR

Question 34

Describe the typical CSF analysis results of: 1. Bacterial meningitis 2. Aseptic meningitis 3. Tuberculous meningitis

Answer 34

**Bacterial meningitis:** * Turbid * High polymorphs * High protein * Low glucose **Aseptic meningitis:** * Clear * High lymphocytes * High protein * Normal glucose **Tuberculous meningitis:** * Clear * High lymphocytes * High protein * Low glucose ## Footnote Abnormal WCC in CSF >5

Question 35

Describe the Gram-stain and microscopic appearance of: 1. *S. pneumonia* 2. *N.meningitidis* 3. *L. monocytogenes* 4. TB 5. *Cryptococcus*

Answer 35

1. ***S. pneumonia*** = Gram-positive alpha-haemolytic diplococci 2. ***N.meningitidis*** = Gram-negative non-haemolytic diplococci 3. ***L. monocytogenes*** = Gram-positive rods 4. **TB** = Stains positively with Ziehl-Neelsen (red and blue) 5. ***Cryptococcus*** = Stains positively with India Ink (appears like an orbit - yeast in the middle with a capsule around the outside) Does not gram stain

Question 36

What is another key clinical feature of Cryptococcal meningitis?

Answer 36

High opening pressure

Question 37

List some limitations of diagnositcs in menigitis.

Answer 37

* MRI oedema pattern may not differentiate between tumour or stroke or vasculitis in some patients * Serology may not be useful in the early stages of infection * Difficulties obtaining CSF * PCR techniques are expensive

Question 38

What is the generic therapy used in meningitis?

Answer 38

* Ceftriaxone 2g IV BD * If \> 50 years or immunocompromised = amoxicillin 2 g IV 4 hourly NOTE: this is because ceftriaxone does NOT cover *Listeria*

Question 39

What it the generic therapy used in meningo-encephalitis?

Answer 39

* Aciclovir 10 mg/kg IV TDS * Ceftriazone 2 g IV BD * If \> 50 years or immunocompromised = amoxicillin 2 g IV 4 hourly

Question 40

Name the specific therapy for meningitis caused by: 1. *S. pneumoniae* 2. *N. meningitidis* 3. *H. influenzae* 4. Group B *Streptococcus* 5. *Listeria* 6. Gram-negative bacilli 7. *Pseudomonas*

Answer 40

**1. *S. pneumoniae* =** Ceftriaxone **2. *N. meningitidis*** = Ceftriazone 4 g/day **3. *H. influenzae*** = Cefotaxime 12 g/day **4. Group B *Streptococcus*** = Pen G 18-24 mu/day **5. *Listeria*** = Ampicillin 12 g/day **6. Gram-negative bacilli** = Cefotaxime 12 g/day **7. *Pseudomonas*** = Meropenem 6 g/day