2.1 CNS Infective Diseases Flashcards
Which demographic is most at risk of meningitis?
Children under 5
What is the most common cause of meningitis?
Infection (bacterial, viral, fungal, parasitic etc.)
How can pathogens gain access to the subarachnoid space?
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
What are the most common bacteria that cause meningitis?
- Pneumococcus (AKA strep. pneumoniae)
- Meningococcus (AKA neisseria meningitidis)
How can bacterial meningitis be spread? Why is this important?
Coughing, sneezing, or direct contact (need to notify close contacts)
Describe the pathophysiology of bacterial meningitis
- 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)
What is thrombophlebitis?
Blood vessel blocked by thrombus formed due to vascular inflammation
What are the classic clinical features of meningitis?
- Fever
- Nuchal rigidity
- Altered mental state
- Headache
- Nausea and vomiting (raised ICP)
What are three signs that may show up in meningitis?
- Nuchal rigidity
- Kernig’s sign (pain on straightening leg when lying flat)
- Brudzinski’s sign (flexion of neck causes flexion of knee)
What is a unique feature of menigococcal meningitis?
- Petechial/ecchymoses rash
- Will not dissappear when pressed
Define encephalitis, macro/microscopically
Macro: dffuse inflammation of the brain parenchyma
Micro: neuronal death, necrosis, astrocytosis
Encephalopathy vs encephalitis
-opathy: Dysfunction without inflammation
-itis: Dysfunction with inflammation
What is the most common causative organism of encephalitis?
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…
Investigations for encephalitis
- Immunohistochemistry
- Electron microscopy
What are arboviruses? What are some of the more common arboviruses that can cause encephalitis?
- Viruses that are transmitted by vectors such as mosquitos
- Common ones include Ross River Virus and Murray River Encephalitis Virus
Common organism in bacterial encephalitis
Mycobacterium tuberculosis
Common cause of parasitic encephalitis
Cerebral malaria
Common cause of fungal encephalitis
Cryptococcal infection
What is the common mechanism of para/post-infectious encephalitis?
Autoimmune/inflammatory
What are the time courses of the different kinds of encephalitis?
Bacterial/viral: Acute
Parasitic/fungal: More insidious
Investigations for meningitis
- Physical exam
- Blood test
- Lumbar puncture (if no raised ICP)
- CT scan
Presenting features of encephalitis
- Altered mental status
- Psychosis/agitation
- Raised ICP (headache, nausea, vomiting)
- Fever
- Seizures
The lasting complications of encephalitis depend on…
Regions of brain area affected
What is a cerebral abscess?
Focal area of suppural infection in the brain parenchyma
Describe cerebral abscess
- Liquefactive necrosis
- Inflammatory mediators > oedema and neutrophils
- Pus forms due to dead neutrophils in necrotic core
- Demarcated by granulation tissue
Outline the pathophysiology of cerebral abscess
- 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
Common causative organisms of cerebral abscess
- Staph auerus
- Norcardia/toxoplasma
What are some conditions that predispose to developing a cerebral abscess?
- Surgery
- Nearby infections (e.g. mastoiditis)
- Haematogenous spread
- Other conditions (e.g. endocarditis)
True or false: most patients with cerebral abscess experience fever, headache, and focal neurological defecits
- False
- This is seen in <20% of patients
Complications of cerebral abscess
- Focal loss of neurons
- Raised ICP (vasogenic oedema); can cause herniation
- If ruptured: meningitis, ventriculitis
Where does infective meningitis most commonly spread from?
Nasopharyngeal colonisation
Meningitis is defined the presence of an abnormal number of ____ in CSF
White blood cells
What is the most common causative organism of community acquired viral meningitis?
Enterovirus
What are the early investigations in a suspected meningitis case?
- CT head
- Lumbar puncture
What blood tests should be ordered if you suspect CNS infection?
- EUC/LFT (alternative cause of drowsiness)
- CBE (Neutrophils: bacterial; lymphocytes: viral etc.)
- Coags (low platelets contraindicate LP)
True or false: you should not give antibiotics for a suspected CNS infection until imaging results have returned
False. This is associated with higher mortality. Do it ASAP.
When might PCR be useful in identifying the causative organism for CNS infection?
When the patient is already on antibiotics
