CNS Infections Flashcards
What are the 3 organisms which cause meningitis in neonates?
- E. coli and other coliforms
- Group B strep
- Listeria
What is meningitis?
Meningitis is inflammation of the meninges.
What is meningism?
The symptoms and signs which accompany the inflammation (a patient with this often has meningitis but not always).
What is encephalitis?
Encephalitis is inflammation of the brain; it can occur independently of meningitis or can occur with meningitis in which case it is called meningoencephalitis.
Describe the clinical presentation of meningitis.
-
Non-specific symptoms
- Fever
- Nausea and vomiting
- Lethargy
- Irritable or unsettled mood, refusal of food and drink, headache, muscle ache or joint pain and respiratory symptoms such as a cough.
-
More specific symptoms and signs
- Stiff neck
- Altered mental state (confusion, delirium and drowsiness, impaired consciousness)
- Non-blanching rash
- Bulging fontanelle (in infants)
- Photophobia
- Kernig’s sign
- Brudzinski’s sign
- Coma
- Paresis
- Focal neurological defecit
- Seizures
Describe other factors in the history which may help confirm diagnosis of meningitis.
- Recent exposure to someone with meningitis.
- A progressive petechial rash is suggestive of meningococcal infection.
- A recent infection (especially respiratory or ear infection).
- Recent travel, particularly to areas with endemic meningococcal disease.
- A history of injection drug use.
- A history of recent or remote head trauma.
- Otorrhea or rhinorrhea.
- HIV infection or risk factors.
- Any other immunocompromising conditions.
What would you find upon examination of a patient with meningitis?
- Fever (not always in neonates)
- Purpuric rash (meningococcal disease)
- Neck stiffness (not always present in infants)
- Bulging fontanelle in infants
- Opisthotonus (arching of back)
- Positive Brudzinski / Kernig signs
- Signs of shock
- Hypotension
- Tachycardia
- Pallor
- Hyperventilation
- Focal neurological signs
- Patient is not symmetrical in some way.
- Altered conscious level
- Papilloedema (rare)
- Sign of raised ICP
What is Brudzinski’s sign?
Flexion of the neck with the child supine causes flexion of the knees and hips.
What is Kernig sign?
With the child lying supine and with the hips and knees flexed, there is back pain on extension of the knee.
The child most probably will not let you straighten their knee.
Describe gram staining.
- Gram staining monopolises the thickness of the peptidoglycan cell wall.
- Gram positive organisms tend to have a very thick layer of peptidoglycan, so they hold on to the first stain methylene blue, so under the microscope they look blue.
- Gram negative has a thinner peptidoglycan layer so they do not hold onto the methylene blue; after washing a counter stain is added (usually safranin or fuchsine) and they appear red.
What are the changes on an FBC associated with different infections?
-
Opening pressure
- Normal = 10-20cm
- Bacterial meningitis = high
- Viral meningitis = normal - high
- Tuberculosis = high
- Fungal = high / very high
-
Colour
- Normal = clear
- Bacterial meningitis = cloudy
- Viral meningitis = ‘Gin’ clear
- Tuberculosis = cloudy / yellow
- Fungal = clear / cloudy
-
Cells
- Normal = <5/ml
- Bacterial meningitis = 100-5000
- Viral meningitis = 5-1000
- Tuberculosis = <500
- Fungal = 0-1000
-
Differential
- Normal = Lymphocytes
- Bacterial meningitis = Neutrophils
- Viral meningitis = Lymphocytes
- Tuberculosis = Lymphocytes
- Fungal = Lymphocytes
What are the contraindications to lumbar puncture?
- Cardiorespiratory instability.
- Focal neurological signs.
- Signs of raised ICP e.g. coma, high BP, low HR or papilloedema.
- Coagulopathy.
- Thrombocytopaenia.
- Local infection at the site of LP.
- If it causes undue delay in starting antibiotics.
Where are most CNS infections acquired from?
The bloodstream
Why is a histoy of particularly respiratory or ear infections important when considering a diagnosis of meningitis?
Local spread
Describe the inflammation associated with meningitis.
- When the BBB is disrupted by inflammation, proteins and cells enter the CSF.
- This permits a more effective immune response and allows rapid entry of drugs which do not penetrate the BBB in the absence of infection.
- Inflammation can cause protein accumulation and fibrin deposition which can occlude the aqueduct and cause hydrocephalus.
How migh a patient get cerebral vein thrombosis.
Intracranial hypertension may incarcerate the brain against the skull leading to cerebral vein thrombosis or ischaemia.
What are the factors which must be fixed during meningitis treatment?
- ABC
- Haemodynamic stability
- Fluid balance
- Electrolyte balance
- Seizures
- Longer term problems
Describe the empirical treatment of bacterial meningitis.
- Cefotaxime I.V. 2g immediately, then 12-hourly or ceftriax-one I.V. 2g immediately, then daily. Treat for 5-14 days, depending on microbiological information and clinical progress.
- Dexamethasone 0.15mg/kg 6-hourly for 4 days commenced just before, or with, antibiotics (omit if unsure that antibiotic treatment is optional).
- For patients over 55 years, who may have listerial meningitis, ampicillin or amoxicillin I.V. 2g 6-hourly should be added.
What are the organisms which cause meningitis in children <5?
- N.meningitidis
- H. influenzae
What is the common cause of bacterial meningitis in young adults?
N. meningitidis
What are the causative organisms of bacterial meningitis in older people?
- S. pneumoniae
- Listeria
What are the causative organisms of bacterial meningitis in immunosuppressed people?
- M. tuberculosis
- Cryptococcus
What is the blood-brain-barrier?
The layers of the meninges, their blood vessels, the arachnoid process and the choroid plexus.
What is bacterial meningitis?
How is it transmitted?
- Bacterial meningitis is a life-threatening condition that can affect all ages but is most common in babies and children.
- Transmission occurs through close contact, droplets or direct contact with respirtory secretions.
