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 is the most common cause of bacterial meningitis when aged > 65 and why do we also add amoxicillin in the treatmeant of bacterial meningitis in patients around this age range ?
Most common cause is still streptococcus pneumoniae
But listeria is also a potential cause again hence amoxicillin given to older people
(note basically think of listeria in immunocompromised patients i.e. really young (neonates), immunocompromosied people and older people because they’re slightly immunocompromised compared to younger adults)
What are the different causes of meningitis that you need to think about in immunocompromised patients ?
The common ones are still the ones you need to be most worried about:
- S. pneumoniae, N. meningitidis, Listeria (think this is the main one)
But they are also at risk of uncommon ones:
- Mycobacterium tuberculosis
- Nocardia asteroides
- Cryptococcus neoformans (AIDS related one)
- Staph. aureus
What organisms do the following risk factors predispose to resulting in meningitis:
- Neurosurgery/ head trauma
- Basilar skull fracture e.g. of the cribriform plate
- Neurosurgery e.g. CSF shunt/ head trauma - S. aureus, S. epidermidis, gram neg bacilli
- Basilar skull fracture e.g. of the cribriform plate - S. pneumoniae, H. influenzae, beta-hemolytic strep group A.
What is the difference between meningoccocal and pneumococcal meningitis ?
- S.pneumoniae (Pneumococcal) Meningitis
- N. meningitidis (Meningococcal) Meningitis
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…)
Where can each of the following organisms be found that are potential causes of bacterial meningitis but they don’t cause problems ?
- Nisseria meningitidis
- H. influenza (note mainly talking about type B H. influenza when in ref to meningitis)
- Streptococcus pneumoniae
- Nisseria meningitidis - Found in the throats of healthy carriers.
- H. influenza - throat microbiota
- Streptococcus pneumoniae - nasopharynx. (note some evidence strep, pneumoniae meningitis also linked to cochlear implants)
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
What is the hospital management of bacterial menigitis ?
- 1st line = IV Ceftriaxone + Dexamethasone
- If penicillin allergy then give – IV chlorampenicol + dexamethasone
What antibiotic would you add along with the standard treatment regime of bacterial meningitis if antibiotic cover for the meningitis being potentially caused by listeria is required and when would this cover be required ?
- Would add in IV amoxicillin along with the standard treatment
- If penicillin allergic then add in Co-trimoxazole instead
- This is required for patients equal to or >60yrs old OR those who are immunnocompromised (including alcoholics and diabetics)
When would you need to add IV vancomycin or rifampicin along with the standard treatment of bacterial meningitis ?
If the patient has had recent travel (within the last 6 months) to a country with high rates of penicillin resistant pneumococci
Some of the countries include:
- Canada
- China
- Croatia
- Pakistan
- Poland
- Spain
- Mexico
- Italy
- USA
- Greece
- Turkey
