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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
Q

In CSF fluid of ‘asepctic’ (viral) meningitis describe the;

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

A

a) clear, slightly cloudy
b) 100-500 lymphocytes (lymphocytic pleocytosis)
c) normal
d) normal

26
Q

In CSF fluid of TB meningitis describe the;

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

A

a) clear, slightly cloudy
b) 100-500 lymphocytes (lymphocytic pleocytosis)
c) high
d) low

27
Q

In CSF fluid of cryptococcal infection describe the;

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

A

a) clear
b) 100-200 lymphocytes (lymphocytic pleocytosis)
c) normal, slightly elevated
d) normal, slightly reduced

28
Q

Which age group does viral meningitis typically affect?

A

Primarily affects children and young adults

29
Q

How do signs and symptoms in viral meningitis differ from bacterial?

A
  • Milder signs and symptoms but longer period of presentation
  • Full recovery expected
30
Q

Main viruses causing viral meningitis?

A
  • 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
Q

Where is TB meningitis typically seen in?

A

Higher incidence in immigrant populations who come from countries with a higher incidence of TB

32
Q

Onset of TB meningitis?

A

Insidious onset (slow growing organism)

33
Q

What is recurrent meningitis defined as?

A
  • >2 episodes meningitis
  • Symptom-free intervals
  • Normal CSF between episodes
  • Must be differentiated from chronic meningitis
34
Q

What is encephalitis?

A

An acute inflammatory process affecting the brain parenchyma

35
Q

Which organism is the common cause of encephalitis?

A
  • Viral infection is the most common and important cause, with over 100 viruses implicated worldwide
    • Over 90% of causes in UK is HSV!!
36
Q

Symptoms of encephalitis?

A
  • Symptoms
  • Fever
  • Headache
  • Behavioural changes
  • Altered level of consciousness
  • Focal neurologic deficits
  • Seizures
37
Q

Most common causes of encephalitis:

A
  • 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
Q

Which organism is the most common cause of sporadic encephalitis in previously healthy?

A

Herpes virus (HSV-1 normally)

39
Q

How will herpes encephalitis typically present?

A
  • 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
Q

WHICH DRUG IS USED IN THE TREATMENT OF HERPES ENCEPHALITIS?

A

Aciclovir

41
Q

What is rabies?

A
  • Acute, progressive viral encephalitis
  • Highest case fatality of any infectious disease
  • One of the most ancient diseases described
  • Model zoonosis
42
Q

Pathogenesis of rabies?

A
  • 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
Q

Where is the infection cycle of rabies completed?

A

In the salivary glands

44
Q

What are the 4 clinical phases of rabies?

A
  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
Q

What is neurosyphilis?

A

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
Q

Early symptomatic forms of neurosyphilis (months to a few years)?

A
  • Acute meningitis
  • Meningovascular; presents with stuttering stroke involving middle cerebral artery
47
Q

Late symptomatic forms of neurosyphilis (>2 years)?

A
  • General paresis (of the insane); paralytic dementia
  • Tabes dorsalis; nerves in dorsal column degenerate
48
Q

Diagnosis of neurosyphilis?

A

Diagnosis by blood & CSF serology

49
Q

Pathophysiology of a brain abscess?

A
  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
Q

Most common organisms causing brain abscesses?

A
  • 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
Q

Clinical presentation of a brain abscess?

A
  • Headache (most)
  • Focal neurological deficit (30-50%)
  • Fever (<50%)
  • Nausea, vomiting
  • Seizures
  • Neck stiffness
  • (Papilloedema)
52
Q

Management of brain abscess?

A
  • 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
Q

Why should choice of antibiotic be carefully considered in brain abscesses?

A
  • 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
Q

Which antibiotics are most appropriate in a brain abscess?

A

Ampicillin, Penicillin, Cefotaxime, Ceftazidime, and Metronidazole achieve therapeutic concentrations in intracranial pus

55
Q

Steroids (dexamethasone) is shown to decrease morbidity and mortality in meningitis caused by which bacteria?

A
  • 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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