CNS Infections

Question 1

What are the different types of primary infections of the central nervous system?

Answer 1

• Meningitis
• encephalitis
• brain abscess

Question 2

What is meningitis?

Answer 2

Meningitis is an infection of the protective membranes that surround the brain and spinal cord (meninges)

Question 3

What is encephalitis?

Answer 3

An uncommon but serious condition in which the brain becomes inflamed (swollen)

Question 4

What is brain abscess (cerebral abscess)?

Answer 4

An abscess caused by inflammation and collection of infected material within the brain tissue

Question 5

Why is meningitis classed as a medical emergency?

Answer 5

It can be very serious if it is not treated quickly

it can cause life-threatening septicaemia and result in permanent damage to the brain or nerves

Question 6

What is the difference between meningitis and meningoencephalitis?

Answer 6

Meningitis refers to an inflammatory process of leptomeninges and CSF

meningoencephalitis refers to inflammation of the meninges and brain parenchyma

Question 7

How can meningitis be classified?

Answer 7

• Acute pyogenic- usually bacterial meningitis
• aseptic - usually viral meningitis, lymphocytic pleocytosis
• chronic - mycobacterium tuberculosis (TBM), spirochetes (neurosyphillis), cryptococcus neoformans

Question 8

How is the onset of chronic meningitis defined?

Answer 8

Chronic meningitis has an onset measured in weeks to months

it is generally defined when symptoms, signs and the CSF remain abnormal for at least 4 weeks

Question 9

What is the major cause of aseptic meningitis syndrome?

What does this mean?

Answer 9

Viruses are the major cause of the aseptic meningitis syndrome

this is used to define any meningitis (infectious or non infectious), particularly one with a lymphocytic pleocytosis, for which a cause is not apparent after initial evaluation and routine stains and cultures of CSF

Question 10

What are the 4 different ways in which infectious agents can enter the CNS?

Answer 10

Haematogenous spread:

• this is the most common and usually via arterial route
• can be retrograde (veins)

Direct implantation:

• most often is traumatic
• iatrogenic (rare)
• congenital (meningomyelocele)

Local extension:

• secondary to established infections
• most often from mastoid, frontal sinuses, infected tooth, etc.

Along peripheral nerves:

• usually viruses such as rabies & herpes zoster

Question 11

What are the clinical features which suggest meningitis?

Answer 11

1. Headache
2. irritable
3. neck stiffness
4. photophobia
5. fever
6. vomiting
7. varying levels of consciousness
8. rash

Question 12

Which groups may have a non-specific presentation of meningitis?

Answer 12

1. Neonates
2. elderly
3. immunosuppressed

Question 13

which organisms tend to cause meningitis in children < 1 month?

Answer 13

• Streptococcus agalactiae
• escherichia coli
• listeria monocytogenes

Question 14

What organisms cause meningitis in a child aged between 1 to 23 months?

Answer 14

• Streptococcus pneumoniae
• Neisseria meningitidis
• Streptococcus agalactiae
• Escherichia coli
• haemophilus influenzae

Question 15

Which organisms tend to cause acute bacterial meningitis in people aged 2-50 years?

Answer 15

1. Streptococcus pneumoniae
2. neissseria meningitidis

Question 16

Which organisms tend to cause acute bacterial meningitis in people aged over 50?

Answer 16

• Streptococcus pneumoniae
• Neisseria meningitidis
• Listeria monocytogenes
• aerobic Gram negative bacilli

Question 17

What is involved in the laboratory diagnosis of meningitis?

Answer 17

• Blood cultures
• lumbar puncture - CSF for microscopy, Gram stain, culture & biochemistry
• EDTA blood for PCR

Question 18

What is the appearance and cells of normal CSF?

Answer 18

It is clear and colourless

cells are 0-5 lymphocytes cu mm

Question 19

What does the CSF look like in bacterial meningitis?

Answer 19

The CSF is cloudy and turbid

Cells - 100-2000 polymorphs cu mm

there are high levels of protein and low levels of glucose

Question 20

What does the CSF look like in “aseptic” / viral meningitis?

Answer 20

The CSF is clear but slightly cloudy

Cells - 10-500 lymphocytes cu mm

there is normal levels of both protein and glucose

Question 21

What does the CSF look like in TB meningitis?

Answer 21

The CSF is clear but slightly cloudy

Cells - 10-500 lymphocytes cu mm

there are high levels of protein and low levels of glucose

Question 22

What does the CSF look like in cryptococcal meningitis?

Answer 22

The CSF is clear

cells - 10-200 lymphocytes

protein is normal or slightly elevated

glucose is normal or slightly reduced

Question 23

Who tends to suffer from viral meningitis?

How may it start?

Answer 23

It primarily affects children and young adults

it has milder signs and symptoms

it may start as a respiratory or intestinal infection, then viraemia

Question 24

What type of cell is raised in the CSF in viral meningitis?

Do people recover?

Answer 24

CSF shows raised lymphocyte count (50-200/cu mm)

protein and glucose are usually normal

full recovery is expected

Question 25

What are the causes of viral meningitis?

Answer 25

* Enteroviruses - Echo, Coxsackie A & B * Paramyxovirus - mumps * Herpes simplex, Varicella Zoster virus * adenoviruses * other - arboviruses, lymphocytic choriomeningitis, HIV

Question 26

What is the onset of tuberculosis meningitis like? Which group of people are more at risk?

Answer 26

It has an insidious onset higher incidence in immigrant populations who come from countries with a higher incidence of TB

Question 27

How severe are complications from tuberculosis meningitis?

Answer 27

High frequency of complications - cranial nerve palsies delayed diagnosis makes complications more likely

Question 28

what is the composition of the CSF like in tuberculosis meningitis?

Answer 28

CSF shows predominantly lymphocytic response but polymorphs also present there is high protein there is low / absent glucose

Question 29

What is encephalitis? What usually causes it?

Answer 29

Encephalitis is an acute inflammatory process affecting the brain parenchyma viral infection is the most common and important cause over 100 viruses are implicated worldwide

Question 30

What are the symptoms of encephalitis? What is the incidence?

Answer 30

* Fever * headache * behavioural changes * altered level of consciousness * focal neurological deficits * seizures incidence of 3.5 - 7.4 per 100,000 persons per year

Question 31

What are the causes of viral encephalitis?

Answer 31

* Herpes viruses * HSV-1 & HSV-2 * varicella zoster virus * cytomegalovirus * epstein-Barr virus * human herpes virus 6 * adenoviruses * influenza A * enteroviruses, poliovirus * measles, mumps & rubella viruses * rabies * arboviruses * ​Japanese encephalitis virus * St. Louis encephalitis virus * West Nile encephalitis virus

Question 32

What is herpes encephalitis? what are the major effects of this and what may there be evidence of?

Answer 32

Most common cause of sporadic encephalitis in previously healthy individuals may be evidence of herpes infection of skin / mucosae causes severe haemorrhagic encephalitis affecting the temporal lobe also focal signs and epilepsy features

Question 33

How many cases of herpes encephalitis are there per year?

Answer 33

2-4 cases per million people per year This may be acute infection, but more commonly there is reactivation of latent infection in the trigeminal nerve ganglion

Question 34

What is the mortality like for herpes encephalitis? How should it be treated?

Answer 34

30% mortality with treatment and 70% mortality without treatment high mortality so treatment is needed urgently with **aciclovir**

Question 35

What is meant by recurrent meningitis? what must it be differentiated from?

Answer 35

* \> 2 episodes of meningitis * symptom-free intervals * normal CSF between episodes must be differentiated from chronic meningitis

Question 36

What is rabies? Why is it important to recognise?

Answer 36

Acute, progressive viral encephalitis highest case fatality of any infectious disease

Question 37

Why is rabies described as a viral zoonosis?

Answer 37

A zoonosis is an infectious disease caused by a pathogen that has jumped from non-human animals to humans

Question 38

How does rabies cause infection? How does it enter the body?

Answer 38

The virus enters through a bite it grows at the trauma site for a week and multiplies it then enters nerve endings and advances towards the ganglia, spinal cord and brain the infection cycle is completed when the virus replicates in salivary glands

Question 39

What are the clinical phases of rabies? what symptoms are experienced during these phases?

Answer 39

**Prodromal phase:** * fever, nausea, vomiting, headache, fatigue * some experience pain, burning, tingling sensations at the site of the wound **Furious phase:** * agitation, disorientation, seizures, twitching, hydrophobia **Dumb phase:** * paralysed, disorientated, stuporous * the dumb phase progresses to the **coma phase**, resulting in death

Question 40

When does neurosyphilis arise?

Answer 40

Asymptomatic neurosyphilis can occur at any stage of syphilis central nervous system invasion occurs early in infection in 30-40% of patients early symptomatic forms occur from months to a few years

Question 41

What are the symptoms of neurosyphilis? How is it diagnosed?

Answer 41

* Acute meningitis * meningovascular (stuttering stroke) * general paresis * tabes dorsalis it is diagnosed by blood & CSF serology

Question 42

What is a brain abscess?

Answer 42

A focal suppurative process within the brain parenchyma (pus in the substance of the brain)

Question 43

what are the 4 different ways in which a brain abscess can form?

Answer 43

* Direct spread from "contiguous suppurative focus" - e.g. from ear, sinuses, teeth * haematogenous spread from a distant focus - e.g. endocarditis, bronchiectasis * trauma - e.g. open cranial fracture, post-neurosurgery * cryptogenic - no focus is recognised in 15-20% of cases

Question 44

What types of pathogens are usually found within a brain abscess?

Answer 44

The bacteria responsible depend on the pathogenic mechanism involved brain abscesses are often mixed (polymicrobial) * streptococci (60-70%) e.g. streptococcus milleri * staphylococcus aureus in 10-15% * anaerobes * Gram negative enteric bacteria * others such as fungi, mycobacterium tuberculosis, toxoplasma gondii

Question 45

What is the clinical presentation of brain abscess?

Answer 45

* Headache (most) * focal neurological deficit (30-50%) * fever (\<50%) * nausea, vomiting * seizures * neck stiffness * papilloedema

Question 46

What is involved in the management of a brain abscess?

Answer 46

Drainage is the treatment of choice, but small abscesses can be treated with antibiotics alone * to urgently reduce intracranial pressure * to confirm diagnosis * to obtain pus for microbiological investigation * to enhance efficiency of antibiotics * to avoid spread of infection into the ventricles

Question 47

What factors must be considered for antibiotic treatment of CNS infections? Which antibiotics achieve therapeutic concentrations in intracranial pus?

Answer 47

* Physiological properties of blood-brain barrier & blood-CSF barrier are distinct * penetration of drugs into CSF and brain tissue differ * **ampicillin, penicillin, cefotaxime, ceftazidime & metronidazole** acheive therapeutic concentrations in intracranial pus

Question 48

What type of steroid is used for CNS infections?

Answer 48

**Dexamethasone** 10mg IV given 15 minutes prior to antibiotics shown to decrease morbidity & mortality in S.pneumoniae but not N.meningitidis