10.3 CNS infections Flashcards
What is the role of the BBB
form a continuous barrier between the blood and brain that restricts transport of ions, molecules, cells and pathogens
What forms the BBB?
Enodthelium lining the brain capillaries
- Intracellular tight junctions
- Limited pinocytic activity
- Basement membrane and astrocyte foot processes
- Specific carrier and transport systems
Where is CSF produced?
Choroid plexus in the ventricles of the brain
What is the normal flow of CSF
Lateral ventricles - third ventricle via intraventricular foramina of munro - fourth ventricle via aqueduct of sylvius - subarachnoid space via foramen of megendie
What forms the choroid plexus?
Capillaries separated from the ventricles by choroid epithelial cells (continuous with ependymal cells of the ventricles)
what prevents pathogen entry into CSF?
Tight junctions between the choroidal epithelial cells
Where are the potential sites for infection in the brain?
Meningitis: inflammation of meninges
Encephalitis: inflammation of the brain
Myelitis: inflammation of the spinal cord
Focal lesions/abcesses
What are the mechanisms of pathogen entry to the brain?
Physical pathway
Haematogenous
Peripheral nerve
Olfactory nerve
What is the physical pathway for pathogens?
BBB/BCB damaged by congenital defect, trauma or surgery, extensions from bone
What are the two kinds of haemogenous entry of pathogens?
Primary: blood infection after entry to the body usually from respiratory tract (neisseria meningiditis, viaral, fungal, bacterial)
Secondary to blood infection from primary focus elsewhere (pneumonia, endocarditis)
What is the peirpheral nerve entry to the brain?
Travel up an affected nerve to the brain - olfactory common as it doesn’t have to travel far
What is the presentation of meningitis?
Photophobia, neck stiffness, headache and fever
What symptoms suggest a cause other than meningitis?
Confusion, seizures, neurological deficitis
What are the extraneural symptoms of meningitis?
Rash, pneumonia, sinusitis, otitis media
What is the fatal form and most common form of meningitis?
Bacterial: FATAL without antibiotics
Viral: most common but usually self limiting
What is the gram stain, risks and associations of strep pneumoniae meningitis?
Gram + dipolococci
Risks: hyposplenism,
What is the gram stain, risks and associations of Neisseria meningitides?
Gram - diplococci
Risks:
What is the gram stain, risks and associations of listeria monocytogenes?
Gram + bacillus
Risks: immunosuppressed (T cell def.), pregnancy and neonates
Associated: Subacute, history of unpast daisy, deli meat, raw salads
What is the gram stain, risks and associations of Group B strep?
Gram + cocci in chains
Risks: neonates
Associations: Maternal colonisaton and chorioamniotitis
What is the gram stain, risks and associations of mycobacterium tuberculosis
Risks: TB exposure in past, immunosuppressed
Associated: subacute-chronic presentation, tuberculomas
What are the common causes of viral meningitis and how do you treat it?
Enterovirus, Herpes simplex 2, varicella zoster, primary HIV
usually self limiting
What are the common causes of fungal meningitis?
Cryptococcus neoformans Cryptococcus gatii (red river gums)
What are the common bacterial causes of meningitis?
Listeria monocytogenes
Mycoplasma pneumoniae
What is usually the cause of spinal epidural abscess and what is it?
Staph aureus
Collection of pus between the outermost layer of meninges and the vertebral column
EMERGENCY
Why is a spinal epidural abscess and emergency?
Can cause irreversible para/quadriplegia due to cord compression or infarction
What do you do to diagnose CNS infection?
Clinical history (inc exposure) Imaging (encepahalitis, brain abscess, epidural abscess) EEG (encephalitis) Lumbar puncture (CSF analysis) Blood cultures Tissue biopsy
What do you measure on lumbar puncture?
Opening pressure
MCS microscopy (cell count +/- gram stain), culture, sensitivity
Protein
Glucose
