CNS infections Flashcards
Define what is meant by the term pyogenic meningitis
Bacterial meningitis
Define what the leptomeninges are
- The two inner meninges – so arachnoid and pia mater
Define pleocytosis
Abnormally large number of lymphocytes in CSF
Define what meningitis is
- Meningitis is an inflammation of the leptomeninges and underlying subarachnoid cerebrospinal fluid (CSF). The inflammation may be caused by infection with viruses, bacteria, other micro-organisms, or non-infective causes.
What are the main types of CNS infections we should know about ?
- Acute pyogenic (bacterial) meningitis
- Acute aseptic (viral) meningitis
- Acute focal suppurative infection e.g. brain abscess
- Chronic bacterial infection (tuberculosis).
- Acute encephalitis is an infection of the brain parenchyma
What are the signs and symptoms of bacterial meningitis in general ?
- Fever (pyrexia), headache.
- Stiff neck, back rigidity, bulging fontanelle (in infants), photophobia.
- Altered mental state, unconsciousness, confusion
- Vomiting
- Non-blanching rash.
- May have seizures
- focal neurological deficits (including cranial nerve involvement and abnormal pupils – papilloedema
- Kernig’s sign (pain and resistance on passive knee extension with hips fully flexed)
- Brudziñski’s sign (hips flex on bending the head forward)
What are the 3 main ways in which meningoccocal infection (nisseria) can present ?
- bacterial meningitis (15% of cases of N. meningitidis)
- septicaemia (25% of cases)
- A combination of the two presentations (60% of cases).
What are the signs/symptoms suggestive of meningoccocal sepicaemia ?
- Toxic/moribund state; altered mental state/decreased conscious level.
- Unusual skin colour (generalised non-blanching petechial rash), capillary refill time more than two seconds;
- cold hands/feet.
- Tachycardia and/or hypotension; respiratory symptoms or breathing difficulty.
- Leg pain.
- Poor urine output.
Meningococcal septicaemia without meningitis does not tend to present with stiff neck, back rigidity, bulging fontanelle, photophobia, Kernig’s sign, Brudziñski’s sign, paresis, focal neurological deficits or seizures.
How does meninoccocal + septicaemia usually present ?
Essentially the normal signs of bacterial meningitis covered + signs of septicaemia
Describe the classic histological appearance of bacterial meningitis
- Shows a thick layer of suppurative exudate covers the leptomeninges over the surface of the brain.
- Microscopically there is neutrophils in the subarachnoid space (polymorphs in the CSF - recall the subarachnoid space contains CSF)
What are some of the complications of bacterial meningitis ?
- Can lead to death
- Common for those who survive (up to 25%) to have some impairment such as; limb loss, deafness, blindness, cerebral palsy, quadriplegia and severe mental impairment.
What are the common causes of bacterial meningitis in neonates (first 28days of life)?
- Group B streptococcus, E.coli, Listeria
Use GEL to remember it
What is the most common cause of bacterial meningitis in children (28days <10yrs)?
- Haemophilus influenzae (note this is not the viral influenza, this is bacterial)
What is the most common cause of bacterial meningitis between ages 10-21?
- Neisseria meningitidis
What is the most common cause of bacterial meningitis when aged >21 and what is the other common cause of it ?
- Streptococcus pneumoniae - most common
- Neisseria menigitidis
What are the different routes to which bacterial meningitis may occur ?
- Nasopharyngeal colonization
- Direct extension of bacteria:
- Parameningeal foci (sinusitis, mastoiditis, or brain abscess)
- Across skull defects/fracture
- From remote foci of infection (e.g., endocarditis, pneumonia, UTI…)
What are the initial investigations done for someone with suspected bacterial meningitis ?
- Take blood for culture and coagulation screen
- Give the standard bacterial meningitis treatment with IV antibiotics (empirical treatment) - this is like the first thing you do when suspecting meningitis
- Take a throat swab which should be plated as soon as practicable by the microbiologist
- Disrupt and swab or aspirate any petechial or purpuric skin lesions for microscopy and culture
Then you will usually do a LP for CSF analyses, but sometimes this is contraindicated and when it is you would do a CT scan first
Following the first initial investigations and starting empirical treatment, a lumbar puncture is generally the next investigation, what the indications to doing a CT scan prior to lumbar puncture ?
- Patient is immunocompromised e.g. HIV/ AIDS, after transplantation
- History of CNS e.g. mass lesion, stroke or focal infection
- New onset seizure
- Presence of papilledema
- Abnormal conscious level (think < or equal to 12)
- Focal neurological deficit - Including dilated nonreactive pupil, abnormalities of ocular motility, abnormal visual fields, gaze palsy, arm or leg drift
What are the contraindications to doing a lumbar puncture ?
- Signs of severe sepsis or rapidly evolving rash
- Resp or cardiac compromise
- On anticoagulant therapy/ known thrombocytopenia
- Infection at the site of LP
- Focal neurological signs
- Presence of papilloedema (this is optic disc swelling suggestive of raised ICP)
- If having continuous or uncontrolled seizures
- GCS < or equal to 12
