MI: CNS Infections and Meningitis Flashcards by P P

What are the routes of entry into the CNS?

Haematogenous
Direct implantation
Local extension
PNS into CNS

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What is the most common route of entry for pathogens?

Haematogenous

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What is aseptic meningitis?

Meningitis that is caused by viruses and is not purulent

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What neurological damage be caused by in meningitis?

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

mortality 10% morbidity 5%

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What are the three types of meningitis?

Acute (hours to days)
Chronic (days to weeks)
Aseptic (caused by viruses so there is no pus)

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Name three organisms that cause acute meningitis.

Neisseria meningitidis
Streptococcus pneumoniae
Haemophilus influenzae

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How many serotypes of N. meningitidis are there?

4 - A, B, C, Y

NOTE: the menigitis vaccine is for meningitis C (although there is one available for meningitis B)

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List some other, rarer bacterial causes of acute meningitis.

Listeria monocytogenes
Group B Streptococcus
Escherichia coli

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How does N. meningitidis enter the body?

Through the nasopharyngeal mucosa in susceptible individuals

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

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How long does N. meningitidis take to cause infection?

< 10 days

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How do N. meningitis present?

50% meningitis
7-10% meningitis and septicaemia

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What are the four processess that occur in septicaemia?

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 deragnement - particularly acidosis
Myocardial failure - and multi-organ failure

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Outline the presentaiton of TB meningitis.

Similar presentation to acute meningitis but takes weeks to present
Tends to occur in immunocompromised patients
Involves the meninges and basal cisterns of the brain and spinal cord

5.5 per 1000 death

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List some complications of TB meningitis.

Tuberculous granulomas
Tuberculous abscesses
Cerebritis

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What is a typical MRI feature of TB meningitis?

Leptomeningeal enhancement

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What is the most common infections of the CNS?

Aseptic meningitis

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What are the most common causative organisms in aseptic meningitis?

enteroviruses: Coxsackie group B viruses

Echoviruses

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Which age group is susceptible to aseptic meningitis?

< 1 year

NOTE: normally self-resolving after 1-2 weeks

How is encephalitis transmitted?

Haematogenous (either person-to-person or through vectors such as mosquitoes)

List some viruses that cause encephalitis.

Mumps
Measles
Enteroviruses
Herpes viruses

What is becoming a leading cause of encephalitis worldwide?

West Nile virus

NOTE: this is transmitted by mosquitoes and birds

Which bacterium is associated with causing encephalitis?

Listeria monocytogenes

Name two types of amoeba that cause encephalitis.

Naegleria fowleri
Acanthamoeba species and Balamuthia mandrillaris

NOTE: these amoebae spread by direct extension (e.g. through the cribiform plates)

What is toxoplasmosis and how is it spread?

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

How do bacteria that cause brain abscesses tend to spread?

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

List some organisms that can cause brain abscesses.

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

Name a common spinal infection.

Pyogenic vertebral osteomyelitis

How can pyogenic vertebral osteomyelitis spread?

Direct open spinal trauma from infections in adjacent structures, haematogenous spread from vertebra

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

* Permanent neurologic defects * Significant spinal deformity * Death

List some risk factors for pyogenic vertebral osteomyelitis.

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

Compare the use of MRI and CT in CNS infections.

MRI is better than CT at detecting parenchymal abnormalities such as abscesses and infarctions

List some other useful tests for suspected meningitis.

* Blood culture * Throat swab * Blood PCR * Sputum culture * Urine culture | CSF sample, brain tissue

What studies can be done with CSF?

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

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

**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

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

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)

What is another key clinical feature of Cryptococcal meningitis?

High opening pressure

List some limitations of diagnositcs in menigitis.

* 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 * methods to detect amoebic infections

What is the generic therapy used in meningitis?

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

What it the generic therapy used in meningo-encephalitis?

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

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*

**1. *S. pneumoniae* =** Pen G 18-24 mu/day **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

what is this and stain

cryptococcus neoformans/ menigitis india ink stain

what is this and stain

TB Ziehl-Neelsen stain

Other considerations in adjunctive therapy for CNS infections

level of care steroids ? repeat LP public health

what is the auramine–rhodamine stain used for

TB also ziehl-neelsen stain