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Medical Studies 2A > 2.1 CNS Infective Diseases > Flashcards

2.1 CNS Infective Diseases Flashcards

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USMLE® Step 1 flashcards
1
Q

Which demographic is most at risk of meningitis?

A

Children under 5

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2
Q

What is the most common cause of meningitis?

A

Infection (bacterial, viral, fungal, parasitic etc.)

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3
Q

How can pathogens gain access to the subarachnoid space?

A

Direct (anatomical defect, otitis media, sinusitis), or indirect (haematogenous spread, adjacent infected areas)

In terms of blood, this often occurs through BSCFB; more permeable than BBB

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4
Q

What are the most common bacteria that cause meningitis?

A
  • Pneumococcus (AKA strep. pneumoniae)
  • Meningococcus (AKA neisseria meningitidis)
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5
Q

How can bacterial meningitis be spread? Why is this important?

A

Coughing, sneezing, or direct contact (need to notify close contacts)

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6
Q

Describe the pathophysiology of bacterial meningitis

A
  • Bacteria enters bloodstream and replicates
  • Bacteria crosses the blood brain barrier, and enters into CSF
  • They undergo lysis, leading to release of inflammatory mediators and immune cell recruitment
  • Increased BBB permeability
  • Cerebral oedema, increasing ICP (secondary to albumin leaking in, creating osmotic gradient)
  • Can lead to thrombophlebitis > infarction
  • Adhesions form between meninges (impinging cranial nerves and causing hydrocephalus)
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7
Q

What is thrombophlebitis?

A

Blood vessel blocked by thrombus formed due to vascular inflammation

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8
Q

What are the classic clinical features of meningitis?

A
  • Fever
  • Nuchal rigidity
  • Altered mental state
  • Headache
  • Nausea and vomiting (raised ICP)
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9
Q

What are three signs that may show up in meningitis?

A
  • Nuchal rigidity
  • Kernig’s sign (pain on straightening leg when lying flat)
  • Brudzinski’s sign (flexion of neck causes flexion of knee)
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10
Q

What is a unique feature of menigococcal meningitis?

A
  • Petechial/ecchymoses rash
  • Will not dissappear when pressed
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11
Q

Define encephalitis, macro/microscopically

A

Macro: dffuse inflammation of the brain parenchyma
Micro: neuronal death, necrosis, astrocytosis

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12
Q

Encephalopathy vs encephalitis

A

-opathy: Dysfunction without inflammation
-itis: Dysfunction with inflammation

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13
Q

What is the most common causative organism of encephalitis?

A

Herpes Simplex Virus (2° to HSV; only 25% of patients have history of cold sores)

Think of Brian from Family Guy, when he gets herpes; he does strange things, maybe he has altered mental status 2° to encephalitis…

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14
Q

Investigations for encephalitis

A
  • Immunohistochemistry
  • Electron microscopy
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15
Q

What are arboviruses? What are some of the more common arboviruses that can cause encephalitis?

A
  • Viruses that are transmitted by vectors such as mosquitos
  • Common ones include Ross River Virus and Murray River Encephalitis Virus
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16
Q

Common organism in bacterial encephalitis

A

Mycobacterium tuberculosis

17
Q

Common cause of parasitic encephalitis

A

Cerebral malaria

18
Q

Common cause of fungal encephalitis

A

Cryptococcal infection

19
Q

What is the common mechanism of para/post-infectious encephalitis?

A

Autoimmune/inflammatory

20
Q

What are the time courses of the different kinds of encephalitis?

A

Bacterial/viral: Acute
Parasitic/fungal: More insidious

21
Q

Investigations for meningitis

A
  • Physical exam
  • Blood test
  • Lumbar puncture (if no raised ICP)
  • CT scan
22
Q

Presenting features of encephalitis

A
  • Altered mental status
  • Psychosis/agitation
  • Raised ICP (headache, nausea, vomiting)
  • Fever
  • Seizures
23
Q

The lasting complications of encephalitis depend on…

A

Regions of brain area affected

24
Q

What is a cerebral abscess?

A

Focal area of suppural infection in the brain parenchyma

25
Q

Describe cerebral abscess

A
  • Liquefactive necrosis
  • Inflammatory mediators > oedema and neutrophils
  • Pus forms due to dead neutrophils in necrotic core
  • Demarcated by granulation tissue
26
Q

Outline the pathophysiology of cerebral abscess

A
  • Pathogen is detected within the brain environment
  • Microglia and astrocytes are recruited, and release inflammatory mediators
  • Mediators enable neutrophils, macrophages, and lymphocytes to enter site of infection, broadening area of inflammation
  • Vascularised granulation tissue walls of infection, but much tissue undergoes necrosis regardless
27
Q

Common causative organisms of cerebral abscess

A
  • Staph auerus
  • Norcardia/toxoplasma
28
Q

What are some conditions that predispose to developing a cerebral abscess?

A
  • Surgery
  • Nearby infections (e.g. mastoiditis)
  • Haematogenous spread
  • Other conditions (e.g. endocarditis)
29
Q

True or false: most patients with cerebral abscess experience fever, headache, and focal neurological defecits

A
  • False
  • This is seen in <20% of patients
30
Q

Complications of cerebral abscess

A
  • Focal loss of neurons
  • Raised ICP (vasogenic oedema); can cause herniation
  • If ruptured: meningitis, ventriculitis
31
Q

Where does infective meningitis most commonly spread from?

A

Nasopharyngeal colonisation

32
Q

Meningitis is defined the presence of an abnormal number of ____ in CSF

A

White blood cells

33
Q

What is the most common causative organism of community acquired viral meningitis?

A

Enterovirus

34
Q

What are the early investigations in a suspected meningitis case?

A
  • CT head
  • Lumbar puncture
35
Q

What blood tests should be ordered if you suspect CNS infection?

A
  • EUC/LFT (alternative cause of drowsiness)
  • CBE (Neutrophils: bacterial; lymphocytes: viral etc.)
  • Coags (low platelets contraindicate LP)
36
Q

True or false: you should not give antibiotics for a suspected CNS infection until imaging results have returned

A

False. This is associated with higher mortality. Do it ASAP.

37
Q

When might PCR be useful in identifying the causative organism for CNS infection?

A

When the patient is already on antibiotics

Medical Studies 2A (110 decks)

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