Meningitis Flashcards
definition of meningitis?
•INFECTION OF BRAIN’S CONNECTIVE TISSUE COVERING
What is the most frequent route of entry for pathogens causing CNS infections ?
Haematogenous spread
what is meningitis
inflammatory process of the meninges and CSF
neurological damage caused by:
- direct bacterial toxicity
- indirect inflammatory processes and cytokine release
- shock, seizures and cerebral hypoperfusion
what are the symptoms of bacterial meningitis?
- HEADACHE. FEVER. DROWSINESS/UNCONSCIOUSNESS.
- ALSO, PHOTOPHOBIA, VOMITING
what are the signs of bacterial meningitis to look out for?
- NECK/SPINE STIFFNESS
- POSSIBLE RASH - DEPENDING ON AETIOLOGY
List 4 routes of entry to the CNS for pathogens
- Haematogenous spread (meningococcus, pneumococcus)
- Direct implantation (after surgery)
- Local extension (from the ear)
- PNS into CNS (rabies)
why is bacterial meningitis considered a medical emergency?
- APPARENT HEALTH TO DEATH IN 24 HOURS
- GREATER MORBIDITY THAN VIRAL
what is the prevalence of bacterial meningitis in the uk?
- 2000 CASES BACTERIAL MENINGITIS PER YEAR IN UK
- 150 DEATHS
differential diagnosis?
- SUBARACHNOID HAEMORRHAGE. CEREBRAL ABSCESS
- CEREBROSPINAL FLUID (CSF) FROM SUBARACHNOID HAEMORRHAGE
what is the colour of the CSF and why?
YELLOW/ORANGE COLOUR: STAINED BY LYSED RBC’s. = “XANTHOCHROMIA”
Which organisms is a common cause of neonatal meningitis ?
Group B streptococcus
Also Listeria monocytogenes
Floral bacteria in the mothers vagina or maternal bacteraemia
which organisms cause meningitis up to 5 years of age?
•Neisseria meningitidis.
Streptococcus pneumoniae.
Haemophilus influenzae (rare in UK).
which organisms cause meningitis from 5 years to 50 years of age?
Neisseria meningitidis.
Streptococcus pneumoniae.
which organisms cause meningitis above 50 years of age?
•Streptococcus pneumoniae.
Neisseria meningitidis.
Rarely: L. monocytogenes and TB
what are the predisposing factors for neonate disease?
- LOW BIRTH WEIGHT (eg premature)
- EARLY RUPTURE OF MEMBRANES
what is the key group of adults predisposed to infection?
immunocomprised
- susceptible to many infections
- yeasts, esp. Cryptococcus neoformans in AIDS
other predisposing factors?
•SINUSITIS,
MASTOIDITIS,
OTITIS MEDIA,
PNEUMONIA,
SKULL FRACTURE,
ALCOHOLISM
What organism commonly causes chronic meningitis ?
Tuberculosis
What organisms can cause aseptic meningitis ?
Enterovirus - coxsackievirus
Herpes simplex
What is aseptic meningitis?
- also known as viral meningitis - no pus found
- Usually acute viral meningitis
- not as severe as bacterial
Which N.meningitidis serotypes are there vaccinations for ?
B and C
What type of meningitis is suggested by this CSF sample ? What are the likely causative organisms ?
CSF appearance: clear
Cells: 0-5 leukocytes
Gram stain/antigen tests: negative results
Protein: 0.15-0.4 g/l
Glucose: 2.2-3.3mmol/m
Normal
No organisms
**ADD TABLE FROM NOTES PLS**
What type of meningitis is suggested by this CSF sample ? What are the likely causative organisms ?
CSF appearance: Turbid
Cells: 100-2000 polymorphs
Gram stain/antigen tests: positive results
Protein: 0.5-3.0 g/l
Glucose: 0-2.2 mmol/l
Purulent meningitis (bacterial)
Meningococcus
Pneumococcus
Listeria
What type of meningitis is suggested by this CSF sample ? What are the likely causative organisms ?
CSF appearance: clear/slightly turbid
Cells: 30-500 lymphocytes/ some polymorphs
Gram stain/antigen tests: negative results (scanty acid fast bacilli)
Protein: 1.0-6.0 g/l (high)
Glucose: 0-2.2 (normal)
Tuberculous meningitis
Mycobacterium TB
Which imaging is best for detecting parenchymal abnormalities e.g. abscesses and infarctions?
Which is more commonly available and so used?
Best: MRI
More used: CT
Culture and microscopy shows a gram +ve, alpha haemolytic diplococcus organism, what is the likely organism causing the meningitis ?
Streptococcus. Pneumoniae
- this is Gram POSITIVE a-haemolytic diplococcus
- Gram positive = pneumococcus (diplococci) = Stains purple on gram stain (Positive = Purple)
- Gram negative = meningococcus = Stains pink on gram stain
Culture and microscopy shows a gram -ve diplococci which is non-haemolytic, what organism is the likely cause of this meningitis ?
What would agar show?
Meningococcus (Neisseria meningitides) - gram NEGATIVE cocci
- stains PINK
Agar would show lots of neutrophils
Culture and microscopy shows gram +ve purple rods, what organism is the likely cause of this meningitis ?
Listeria monocytogenes
A 45-year-old presents with headache and neck stiffness over a period of weeks. LP shows cuboidal structures that appear red against a blue stain. What is the causative pathogen?
TB
- NB this happens over WEEKS (chronic meningitis cause)
- This is Ziehl-Neelsen stain
India ink stain: shows orbit structures (yeast cells with surrounding halos)
Lumber puncture: high opening pressure
IN a patient with HIV
What is the likely causative organism of this meningitis ?
Cryptococcus Neoformans
Which organism commonly causes meningitis in men who have sex with men (MSM)
Cryptococcus Neoformans
Which drug is effective against Meningococcus, pneumococcus, haemophilus and e.coli ?
Ceftriaxone I.V
Which drug is effective at treating Listeria ?
Amoxicillin
Which organism is most commonly associated with recurrent aseptic meningitis (Mollaret’s meningitis) ?
HSV-1 and HSV-2
Which organisms are the most common cause of aseptic meningitis ?
Enterovirus (80%) - Echovirus, coxsackie virus
common causes of myelitis
poiovirus
common causes of neurotoxin release
clostridium tenani
clostridium botulinum
list other causes of meningitis
listeria monocytogenes
group B strep
E. coli
rare:
TB, S. Aureus, T. Pallidum, cryptococcus neoformans
describe the processes whereby septicaemia occurs
- capillary leak - albumin and other plasma proteins lead to hypovolaemia
- coagulopathy - leads to bleeding and thrombosis
- metabolic derrangeent - acidosis
- myocardial failure and multi-organ failure
complications of TB meningitis
- common in immunosuppressed
- complications = tuberculosis granulomas
- tuberculosis abscesses
- cerebritis
- there is leptomeningeal enhancement
features of aseptic meningitis
- most common infection of the CNS
- coxsackie group B
- echoviruses
- usually in children <1 year
- self-limiting, resolves in 1-2 weeks
How to clinically differentiate encephalitis from meningitis
The disturbance of cognitive function in ecephalitis is what differentiates meningitis to encephalitis
4 samples to send for Ix if meningitis suspected
- CSF
- Blood culture
- Throat swab
- Sputum culture
What colour does gram positive stain?
Stains purple on gram stain (Positive= Purple)
- e.g. Gram positive = pneumococcus (diplococci)
What colour does gram negative stain?
Stains pink on gram stain e.g. meningicoccus)
Which group tend to be infected more by listeria for meningitis? (2)
- Old age (have age-related immunosenescence)
- Immunosuppressed pts
Most common infection of CNS
Which age group does it mainly affect?
How does it resolve?
Aseptic Meningitis (viral)
Mainly affects children < 1 year
Self-limiting condition (resolves over 1-2 weeks) - NO antivirals
how can aseptic meningitis be treated?
- Aciclovir for HSV meningitis
- Other antivirals: not effective or not evaluated
Which group of pts are mainly affected by chronic meningitis + what is common causative organism?
- group: immunosuppressed + old
- common organism: TB
what is the key group of adults predisposed to infection?
immunocomprised
- susceptible to many infections
- yeasts, esp. Cryptococcus neoformans in AIDS
what is CSF?
CEREBROSPINAL FLUID
what is the cerebrospinal fluid?
- Brain’s blood vessels
- Very tight intercellular junction
- Lack of pinocytosis
- Forms the basis of the “Blood-Brain Barrier”
what is the problem with the blood-brain barrier?
- Has a protective function, but:
- Results in low antibody and WBC levels in CSF
what is the result if organisms do penetrate the barrier?
Are temporarily relatively protected from immune system
normal CSF characteristics?
< 5 WBC’s/mm3 ~ 75% polymorphs,
20% lymphocytes
2/3 plasma glucose.
Clear. Sterile.
CSF characteristics in bacterial meningitis?
1000 - 10000 WBC’s/mm3.
Increased polymorphs¯ glucose.
Turbid. +/- Visible organisms in smear
CSF characteristics in aseptic meningitis?
50 - 1500 WBC’s/mm3.
Lymphocytes predominant
Normal glucose. Clear.
CSF characteristics in tuberculous meningitis?
<1000 WBC’s/mm3.
Lymphocytes predominant
or normal glucose
can CSF be used for diagnostics?
Useful sample - rapid diagnosis by microscopy
and PCR for genome detection
•Antigen detection using specific antisera
does genome detection work for all
how is sampled obtained?
obtained by lumbar puncture
Potentially dangerous to obtain
what microscopy is used?
•Gram stain, WBC cell count, WBC differential count
how is sample cultured?
Blood agar in 5% CO2
Chocolate agar in 5% CO2
Blood agar - anaerobic
Antibiotic sensitivity testing
is it worth doing blood cultures?
yes
40% cases due to N. meningitidis and S. pneumoniae are positive
what else about blood samples?
- Whole blood more useful than serum
- PCR for genome detection
what other diagnostic tests are helpful?
rash biopsy and throat swab
for microscopy (rash biopsy), culture and antibiotic sensitivities
MENINGOCOCCAL DISEASE IS CAUSED BY?
Neisserria meningitidis
MENINGOCOCCAL DISEASE
can cause septicemia or meningitis or both
septicemia has higher mortality rate
how many neisserria meningitdis serotypes are there?
3
A, B, C
most common in Uk?
B
commonest worldwide?
A
which incidence tripled in 5 years prior to Men-C vaccine?
C
where is the bacteria found in 25% adults?
•NORMAL NASOPHARYNX FLORA
how is infection spread?
INFECTED RESPIRATORY SECRETIONS
what is the route of infection?
•INHALATION ⇢ NASOPHARYNX ⇢ BLOOD STREAM ⇢ INVADE BBB CELLS ⇢ MENINGEAL SPACE
when does infection occur?
SHORTLY AFTER COLONISATION
PROBABLY BEFORE IMMUNE RESPONSE HAS DEVELOPED
what is the treatment?
•BENZYLPENICILLIN OR CEFOTAXIME
how to identify bacteria?
Gram negative diplococci
what media will grow well on?
enriched media in 5% CO2
Eg chocolate agar
what other identifying characteristics?
- Oxidase positive
- Ferment glucose and maltose
- DNA’ase negative
how can antibodies be used in identification?
•Slide agglutination with antibodies directed against meningococcal polysaccharides
how can pcr be used in identification?
identifying ctrA and siaD gene
the ctrA gene?
- Export of polysaccharide capsule
- Common to all meningococci
when used pcr screening be used to be find ctrA gene?
invasive N. meningitidis disease
the siaD gene?
Capsular synthesis
- Serogrouping assay
- Epidemiological value
