CNS infection - meningitis and encephalitis Flashcards
Define meningitis
inflammation of the leptomeninges (the arachnoid and pia mater) and usually occurs due to a bacterial, viral, or fungal infection.
Most common cause of bacterial meningitis in the UK
Neisseria meningitidis and S pneumoniea - most common in adults is S. pneumoniae
Most commomn cause of viral meningitid
enterovirus
coxsackievirus
Common bacterial causes of MG?
- Group B strep,
- e coli
- s pneumoniea
- m tuberculosis
- Neisseria mengitidis
common fungal causes of mg
cryptococcus neoformans
candida albicans
Rf for mg
- Immunocompromised: numerous causes includingextremes of age(children and the elderly),infection(such as HIV) andmedication(such as chemotherapy)
- Non-immunised: at risk ofH. influenza, pneumococcal and meningococcal meningitis
- Crowded environment: students living in halls of residence are a commonly affected demographic
two methods of transmission for MG
Direct spread
Haematogenous
How does direct spread occur
- pathogen gets inside the skull or spinal column, and then penetrates the meninges ending up in the CSF
- sometimes the pathogen will come on open skin or through nose
how does haematogenous spread occur
Pathogen enters the bloodstream and moves through the endothelial cells in the blood vessels making up the blood-brain barrier and gets into the CSF.
What happens once a pathogen enters the CSF
- begins to multiply
- wbc release cytokines to recruit additional immune cells
- more than 5microlitres will suggest meningitid
what happens to glucose and protein levels in the csf
- glucose in csf falls to below 2/3 of the blood
- protein increases
Signs of meningitis
- Kernig’s sign: when the hip is flexed and the knee is at 90°, extension of the knee results in pain
- Brudzinski sign: severe neck stiffness causes the hips and knees to flex when the neck is flexed
- Petechial or purpuric non-blanching rash: associated with meningococcal disease (N. meningitidis)
- Pyrexia
- Reduced GCS
Symptoms of meningitis
- meningism - headache, photophobia, neck stiffness
- fever
- nausea and vomitting
- seizures
Investigations for MG
- fbc- leukocytosis
- CRP - raised inflammatory markers
- coagulation and blood glucose required for comparison
Lumbar puncture and CSF analysis
- CSF gram stain:S. pneumoniae(gram-positive cocci in chains);N. meningitidis(gram-negative diplococci)
- CSF culture
- CSF PCR:useful for viruses such as HSV and VZV
- CSF interpretation
primary care management of MG
IV or IM benzylpenicillin STAT
Bacterial management of MG
- Steroids; dexamethasone - to reduce long term neurological symptoms -
- Antibiotics
3-50yrs = IV cefotaxime
Over 50 = Iv cefotaxime and amoxicillin
Viral management of MG
- Aciclovir
- conservative management
Complications of MG
- Abscess
- Cerebral oedema
- Hydrocephalus and brain herniation
- Seizures
- Sensorineural hearing loss
- Waterhouse- Friderichsen syndrome
What is encephalitis
- inflammation of the brain paarenchyma, mostly affects frontal and temporal lobes
Most common cause of encephalitis
Herpes simplex virus
Other causes of encephalitis
- Enteroviruses
- Flaviviruses
- Retroviruses
- TB
- Syphilis
Rf for EC
- Immunocompromise
- Blood/fluid exposure:HIV and West Nile virus
- Mosquito bite: West Nile virus
- Transfusion and transplantation: CMV, EBV, HIV
- Close contact with cats: toxoplasmosis
Pathophsyiology of EC
- Encephalitis is an immune response to the invasion of a pathogen, causing inflammation of the brain parenchyma.
Describe what happens in EC
HSV gets into the sensory ganglia by travelling retrograde from skin and recurrent infection happens when it travels anterograde back to the skin. If it travels to the CNS, it leads to encephalitis. This is usually along olfactory or trigeminal nerves.
SIGNS OF EC
- Pyrexia
- Reduced GCS
- Focal neurological deficit, such as:
- Aphasia
- Hemiparesis
- Cerebellar signs
- May also have signs of meningitis: meningo-encephalitis
Symptoms of EC
- Fever
- Headache
- Fatigue
- Confusion
- Seizures
- Behavioural changes:
- Memory disturbance
- Psychotic behaviour
- Withdrawal or change in personality
Primary investigations of EC
- Blood tests:FBC, CRP, U&Es and blood culture
- Throat swab:culture for viral organisms
- HIV serology: now routinely tested in the emergency department
- CT or MRI head:MRI is preferred and will show evidence of inflammation in the medial temporal and inferior frontal lobes in HSV encephalitis;CTis normal in ⅓ of cases
Lumbar puncture analysis for EC
- Analysis:lymphocytosis with raised protein in the case of viral aetiology
- PCR:assays for common viral infections including HSV should be carried out
- Culture:useful for bacterial causes
- Serology:antibodies against specific viral antigens
DD for ec
- Meningitis
- Encephalopathy
- Status epilepticus
- CNS vasculitis
Management of EC
Antiviral med- aciclovir
Ganciclovir
Encephalitis MRI
Bilateral medial temporal lobe involvement very supportive of encephalitis
