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Yr 2 - Clinical Pathology > CNS Infections > Flashcards

CNS Infections Flashcards

1
Q

What are the 3 main different types of primary infections of the CNS?

A
  1. Meningitis
  2. Encephalitis
  3. Brain abscess
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2
Q

What is a brain abscess?

A

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

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3
Q

What are the leptomeninges?

A

The inner two meninges, the arachnoid and the pia mater, between which circulates the cerebrospinal fluid.

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4
Q

Meningitis vs meningoencephalitis?

A
  • Meningitis refers to an inflammatory process of leptomeninges and CSF
  • Meningoencephalitis refers to inflammation to meninges and brain parenchyma
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5
Q

What are the 3 classifications of meningitis?

A
  1. Acute pyogenic
  2. Aseptic
  3. Chronic
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6
Q

What is acute pyogenic meningitis typically caused by? (3 organisms)

A

Usually bacterial meningitis;

  1. Haemophilus influenzae
  2. Streptococcus pneumoniae
  3. Neisseria meningitidis
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7
Q

What is aseptic meningitis?

A

Aseptic meningitis is the inflammation of the meninges, a membrane covering the brain and spinal cord, in patients whose cerebral spinal fluid test result is negative with routine bacterial cultures.

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8
Q

Which organisms is aspeptic meningitis typically caused by?

A

Usually viral meningitis

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9
Q

What is lymphocytic pleocytosis?

A

Lymphocytic pleocytosis is an abnormal increase in the amount of lymphocytes in the cerebrospinal fluid (CSF).

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10
Q

Which organisms is chronic meningitis typically caused by?

A

Mycobacterium tuberculosis (TBM), spirochetes (neurosyphilis), Cryptococcus neoformans

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11
Q

When can meningitis be defined as chronic?

A

Has an onset measured in weeks to months (but is generally defined when symptoms, signs, and the CSF remain abnormal for at least 4 weeks)

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12
Q

4 ways that infectious agents can enter the CNS?

A
  1. a) Haematogenous spread
    • most common
    • usually via arterial route
    • can be retrograde (veins)
  2. b) Direct implantation
    • i) most often is traumatic
    • ii) iatrogenic (rare)
    • iii) congenital (meningomyelocele)
  3. c) Local extension
    • Secondary to established infections: most often from mastoid, frontal sinuses, infected tooth, etc.
  4. d) Along peripheral nerves; usually viruses e.g. Herpes Zoster
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13
Q

Pathogenesis of meningitis?

A
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14
Q

Which virus can travel along peripheral nerves and enter the CNS?

A

Herpes Zoster

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15
Q

A local extension of established infections can lead to infection of the CNS. Where are these infections usually originating from?

A

Most often from mastoid, frontal sinuses, infected tooth, etc.

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16
Q

Which organisms most commonly cause acute bacterial meningitis in;

  • <1 month olds
  • 1-23 month olds
  • 2-50 year olds
  • >50 year olds
A
  • a) Streptococcus agalactiae, Escherichia coli, Listeria monocytogenes
  • b) Streptococcus pneumoniae, Neisseria meningitidis Streptococcus agalactiae, Escherichia coli, Haemophilus influenzae
  • c) Streptococcus pneumoniae, N.meningitidis
  • d) Streptococcus pneumoniae, N. meningitidis, Listeria monocytogenes, aerobic Gram negative bacilli
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17
Q

Why is the management of meningitis caused by Listeria monocytogenes different?

A

Listeria is NOT susceptible to usual cephalosporins used!

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18
Q

How is Listeria monocytogenes typically spread?

A

Contaminated food e.g. unpasturised dairy

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19
Q

What is meningism?

A

Clinical syndrome of headache, neck stiffness and photophobia (often with nausea & vomiting)

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20
Q

Clinical features of meningitis?

A
  • Meningism
  • Headache
  • Irritable
  • Neck stiffness
  • Photophobia
  • Fever
  • Vomiting
  • Varying levels of consciousness
  • Rash
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21
Q

Which groups can have non-specific symptoms of meningitis?

A
  • Neonates
  • Elderly
  • Immunosuppressed
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22
Q

Laboratory diagnosis of meningitis?

A
  • Blood cultures
  • Lumbar puncture: CSF for microscopy, Gram stain, culture & Biochemistry
  • EDTA blood for PCR
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23
Q

In normal CSF fluid, describe the;

a) appearance
b) cells
c) protein levels
d) glucose levels

A

a) clear, colourless
b) 0-5; lymphocytes
c) very little protein
d) the glucose level in CSF is proportional to the blood glucose level

24
Q

In CSF fluid of bacterial meningitis describe the;

a) appearance
b) cells
c) protein levels
d) glucose levels

A

a) cloudy, turbid
b) 100-200 polymorphs
c) high protein
d) low glucose

25
In CSF fluid of 'asepctic' (viral) meningitis describe the; a) appearance b) cells c) protein levels d) glucose levels
a) clear, slightly cloudy b) 100-500 lymphocytes (lymphocytic pleocytosis) c) normal d) normal
26
In CSF fluid of TB meningitis describe the; a) appearance b) cells c) protein levels d) glucose levels
a) clear, slightly cloudy b) 100-500 lymphocytes (lymphocytic pleocytosis) c) high d) low
27
In CSF fluid of cryptococcal infection describe the; a) appearance b) cells c) protein levels d) glucose levels
a) clear b) 100-200 lymphocytes (lymphocytic pleocytosis) c) normal, slightly elevated d) normal, slightly reduced
28
Which age group does viral meningitis typically affect?
Primarily affects **children** and **young adults**
29
How do signs and symptoms in viral meningitis differ from bacterial?
* Milder signs and symptoms but longer period of presentation * Full recovery expected
30
Main viruses causing viral meningitis?
* May start as **respiratory** or **intestinal infection** then viraemia * Enteroviruses: Echo, Coxsackie A, B * Paramyxovirus: Mumps * Herpes simplex, Varicella Zoster virus * Adenoviruses * Other: Arboviruses, Lymphocytic choriomeningitis, HIV
31
Where is TB meningitis typically seen in?
Higher incidence in **immigrant** **populations** who come from countries with a higher incidence of TB
32
Onset of TB meningitis?
**Insidious** onset (slow growing organism)
33
What is recurrent meningitis defined as?
* \>2 episodes meningitis * Symptom-free intervals * Normal CSF between episodes * Must be differentiated from chronic meningitis
34
What is encephalitis?
An acute inflammatory process affecting the brain parenchyma
35
Which organism is the common cause of encephalitis?
* Viral infection is the most common and important cause, with over 100 viruses implicated worldwide * Over 90% of causes in UK is **_HSV_!!**
36
Symptoms of encephalitis?
* Symptoms * Fever * Headache * Behavioural changes * Altered level of consciousness * Focal neurologic deficits * Seizures
37
Most common causes of encephalitis:
* **Herpes viruses** – HSV-1, HSV-2, Varicella Zoster virus, Cytomegalovirus, Epstein-Barr virus, Human Herpes virus 6 * Adenoviruses * Influenza A * Enteroviruses, Poliovirus * Measles, Mumps, and Rubella viruses * Rabies * Arboviruses: Japanese encephalitis; St. Louis encephalitis virus; West Nile encephalitis virus
38
Which organism is the most common cause of sporadic encephalitis in previously healthy?
Herpes virus (HSV-1 normally)
39
How will herpes encephalitis typically present?
* May be evidence of **herpes infection** of skin, mucosae * Causes severe **haemorrhagic encephalitis** affecting temporal lobe * Focal signs and epilepsy features * Acute infection or more commonly **reactivation** of latent infection (trigeminal nerve ganglion)
40
WHICH DRUG IS USED IN THE TREATMENT OF HERPES ENCEPHALITIS?
**Aciclovir**
41
What is rabies?
* Acute, progressive viral **encephalitis** * Highest case fatality of any infectious disease * One of the most ancient diseases described * Model zoonosis
42
Pathogenesis of rabies?
* Virus enters through **bite**, grows at trauma site for a week and multiplies, then **enters nerve endings** and advances toward the **ganglia**, **spinal** **cord** and **brain** * Infection cycle completed when virus replicates in the **salivary** **glands**
43
Where is the infection cycle of rabies completed?
In the salivary glands
44
What are the 4 clinical phases of rabies?
1. **Prodromal phase** – fever, nausea, vomiting, headache, fatigue; some experience pain, burning, tingling sensations at site of wound 2. **Furious phase** – agitation, disorientation, seizures, twitching, hydrophobia 3. **Dumb phase** – paralyzed, disoriented, stuporous 4. Progress to **coma phase**, resulting in death
45
What is neurosyphilis?
Infection of the CNS in a patient with syphilis; * Central nervous system invasion occurs early in infection in 30-40% of patients * Asymptomatic neurosyphilis can occur at any stage of syphilis
46
Early symptomatic forms of neurosyphilis (months to a few years)?
* Acute meningitis * Meningovascular; presents with stuttering stroke involving middle cerebral artery
47
Late symptomatic forms of neurosyphilis (\>2 years)?
* General paresis (of the insane); paralytic dementia * Tabes dorsalis; nerves in dorsal column degenerate
48
Diagnosis of neurosyphilis?
Diagnosis by blood & CSF serology
49
Pathophysiology of a brain abscess?
1. Direct spread from “contiguous” suppurative focus (e.g. from ear 40%, sinuses, teeth) 2. Haematogenous spread from a distant focus e.g. endocarditis, bronchiectasis (often multiple abscesses) 3. Trauma (e.g., open cranial fracture, post-neurosurgery) 4. Cryptogenic (no focus is recognised ~15-20 per cent of cases).
50
Most common organisms causing brain abscesses?
* 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 percent) 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
51
Clinical presentation of a brain abscess?
* Headache (most) * Focal neurological deficit (30-50%) * Fever (\<50%) * Nausea, vomiting * Seizures * Neck stiffness * (Papilloedema)
52
Management of brain abscess?
* **Drainage** is treatment of choice (N.B small abscesses can be treated with antibiotics alone) to: * 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
53
Why should choice of antibiotic be carefully considered in brain abscesses?
* Physiological properties of blood-brain barrier and blood CSF-barrier are distinct SO only certain drugs penetrate BBB * Penetration of drugs into CSF and brain tissue differ
54
Which antibiotics are most appropriate in a brain abscess?
Ampicillin, Penicillin, Cefotaxime, Ceftazidime, and Metronidazole achieve therapeutic concentrations in intracranial pus
55
Steroids (dexamethasone) is shown to decrease morbidity and mortality in meningitis caused by which bacteria?
* 10mg IV 15 minutes prior to antibiotics * Shown to decrease morbidity & mortality in **S. pneumoniae** but NOT N. meningitidis

Yr 2 - Clinical Pathology (80 decks)

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