Acute bacterial meningitis Flashcards
What are the pathogens that cause acute bacterial meningitis?
- Neonates: group B Streptococcus, E coli, Listeria
- child: Haemophilus influenzae, Streptococcus pneumoniae
- elderly: : Listeria, Streptococcus pneumoniae
- Adult: Strep pneumoniae > Neisseria meningitis > Haemophilus influenzae > Listeria monocytogenes
- Post-op: Pseudomonas aeruginosa, MRSA, Gram negatives
What is the presentation of acute bacterial meningitis?
-Classic triad of acute bacterial meningitis (41%): fever, nuchal rigidity, altered mental state (AMS), usually of sudden onset (older patients more commonly present with this triad than
younger patients)
- Most common findings: severe headache , fever T > 38, neck stiffness , GCS < 14, nausea
- Absence of all of these findings essentially excludes the presence of bacterial meningitis
- Altered mental status (AMS, i.e. GCS < 15) 🡪 encephalitis component, i.e. meningoencephalitis, not true meningitis alone
- Concomitant infection: sinusitis/otitis (34%), pneumonia (9%), endocarditis (1%)
what is Kernig sign?
Kernig’s is performed by having the supine patient, with hips and knees flexed, extend the leg passively. The test is positive if the leg extension causes pain.
What is Bruzunski’s sign?
Brudzinski’s sign is positive when passive forward flexion of the neck causes the patient to involuntarily raise his knees or hips in flexion.
What are poor prognostic features of acute bacteria meningitis?
- Coma
- Seizures
- Hypotension
- Respiratory distress,
- Peripheral leukopenia
- Peripheral hypernatremia,
- High CSF protein, low CSF glucose
- Specific to meningococcal meningitis: cyanosis, petechiae, metabolic acidosis, oliguria, deranged coagulation
- Pneumococcal meningitis itself is a poor prognostic feature
How would you investigate acute bacterial meningitis?
Blood c/s (STAT, x2, prior to initiation of antimicrobials): Useful if CSF cannot be obtained before administering antimicrobials
FBC
- TW/WCC is usually raised, with left shift (towards immature forms)
- Leukopenia, thrombocytopenia is a/w severe infx and poor outcome
U/E/Cr, BUN, blood glucose POCT (useful to determine CSF/blood glucose ratio)
- CSF/blood glucose ratio is used because CSF glucose (mg/dL) could be: (1) falsely low (< 40 mg/dL) in hypoglycaemia, or (2) incorrectly interpreted as normal when patient is hyperglycaemic (e.g. DM)
- Normal CSF/blood glucose ratio = 0.6-0.7
- If decreased ratio 🡪 glucose consumption by glycolysis from leukocytes and bacteria in CSF 🡪 bacterial meningitis, TB meningitis
CT head shows no raised ICP 🡪 proceed with LP screening for elevated opening pressure lumbar puncture
Lumbar puncture (LP) results
- Increased CSF white blood cell (WBC) count (100-10,000 cells/uL), predominantly neutrophilic
- Increased CSF protein level (> 50 mg/dL)
- Decreased CSF glucose level (< 40% simultaneous serum glucose)
- Gram stain and culture screen
What is the pathogenesis behind acute bacterial meningitis?
- Pathogen invades mucosa, blood, meninges, inflammatory response in subarachnoid space occurs with cerebral oedema.
- Inflammation of blood vessels in subarachnoid space may result in thrombosis, ischaemia and infarction.
What are the predisposing factors for meningitis caused by streptococcus pneumonae?
All conditions that predispose to pneumococcal bacteraemia, fracture of cribriform plate, cochlear implants, cerebrospinal fluid otorrhea from basilar skull fracture, defects of the ear ossicle (Mondini defect)
What are the predisposing factors for meningitis caused by listeria monocytogenes?
Defects in cell-mediated immunity (e.g. glucocorticoids, transplantation [especially renal transplantation]), pregnancy, liver disease, alcoholism, malignancy
What are the predisposing factors for meningitis caused by coagulase negative staphylococci?
Surgery and foreign body, especially ventricular drains
What are the predisposing factors for meningitis caused by staphylococcus aureus ?
Endocarditis, surgery and foreign body, especially ventricular drains; cellulitis, decubitus ulcer (pressure ulcer)
What are the predisposing factors for meningitis caused by GNR?
Advanced medical illness, neurosurgery, ventricular drains, disseminated strongyloidiasis
What are the predisposing factors for meningitis caused by haemophilus influenzae ?
Diminished humoral immunity
What clinical findings point towards listeria as an aetiology of meningitis?
seizures + focal neurological deficits early, or rhombencephalitis (ataxia, cranial nerve palsies, and/or nystagmus), most frequent CN affected is CN8, reflected by hearing loss
What clinical findings point towards neisseria meningitidis as an aetiology of meningitis?
[Rash] non-blanching petechiae, palpable purpura, or [Joints] septic arthritis
