CNS Infections Flashcards
How can chickenpox cause stroke?
Varicella virus reactivated in adulthood causes shingles
Infection of the blood vessels of the brain can cause restriction and clotting
This can later cause stroke
How can a microbe affect CNS function?
Immune mediate CNS damage
-Acute disseminated encephalomyelitis (autoimmune attack)
-Infection triggered antibody associated (post viral encephalitis)
-Immune reconstitution inflammatory syndrome (HIV medication)
Infection triggered metabolic catastrophes
-Reye’s syndrome
-Acute necrotising encephalopathy
Toxin mediated diseases
-Tetanus
Systemic sepsis
-Septic encephalopathy
What factors affect neurovirulence?
Infectious dose
Host immune system
Neurovirulent features of the organism
How do CNS infections cause brain damage?
Inflammation
-BBB breakdown
-Cytokine release
-Endarteritis and thrombosis
Raised ICP
Direct neuronal injury
What are Koch’s postulates?
Microbe must be present in every case
Microbe must be isolated fr the diseased host and grown in pure culture
The disease must be reproduced when a pure culture is introduced to a susceptible host
The microbe must be recoverable from the experimentally infected host
What are the issues with Koch’s postulates?
Might not have an animal model for that disease (human only)
Not every pathogen can be grown in more culture
How is the likelihood of a pathogen being the causative agent evaluated?
Immune response in blood or CSF
What types of neuro infection are there?
Meningitis (enterovirus, mumps)
Ventriculitis (CMV)
Encephalitis (HSV-1)
Myelitis (poliomyelitis)
Radiculitis, ganglionitis (shingles, Bell’s palsy)
What kind of tests can you do on CSF?
Cell count and cytology
Gram stain
Antigen detection
Microbial culture (meningitis)
CSF:plasma glucose or lactate (drop indicates bacterial infection)
PCR (viral)
Antibody tests
What are the cardinal symptoms of encephalitis?
Fever
Alteration in consciousness level
Seizures
How might the neurological/neuropsychiatric symptoms help elucidate aetiology?
Some pathogens have focal preferences
eg HSV and limbic encephalitis
What viruses would be investigated for an immunocompetent patient presenting with encephalitis in the UK
HSV
VZV (chickenpox)
Enteroviruses
Which imaging technique is better at picking up early herpes encephalitis?
MRI
What causes periodic lateralised epileptiform discharges on EEG?
Any severe damage to the temporal lobe
What is the gold standard for diagnosis of herpes encephalitis?
Brain biopsy (rarely needed)
What is the first line investigation of herpes encephalitis?
CSF PCR (95% sensitivity/specificity)
Might get a negative very early or late in disease
How does aciclovir work?
Inhibits viral replication
(Competitive inhibitor or viral DNA polymerase)
What is the mortality rate for herpes encephalitis?
20%
What are the most common sequelae after herpes encephalitis?
Memory impairment
Behavioural changes
Dysphasia
Epilepsy
What are the most common bacterial causes of meningitis?
Meningococcus
Pneumococcus
How do viral and bacterial menigitidies differ in severity?
Bacterial - high morbidity and mortality
Viral - largely benign, treatment is symptom alleviation
What are the symptoms of bacterial meningitis?
Headache
Fever
Meningismus (neck stiffness)
Sensory alteration
Vomiting
Seizures
What are risk factors for pneumococcal meningitis?
Very young or old
Immunocompromised - asplenic
Alcoholism and malnutrition
Chronic disease (diabetes, kidney disease)
Base of skull fracture (entry point)
How would you investigate for pneumococcal meningitis?
Blood cultures
CSF if not contraindicated
What is the treatment for pneumococcal meningitis?
Cephalosporin
Further antibiotics if risk of resistance
What is a useful adjunct to antibiotics for meningitis treatment?
Steroids (dexamethasone)
What is an emerging infection?
Not previously recognised by medical science
or
Have jumped a species barrier
or
Have transplanted to a discrete geographical area where previously not found
