Pathophysiology II - Exam 4/CBL 3 - CNS Infections 🧫

describe the morbidity and mortality rates associated with meningitis

morbidity

- 15-40% experience neurologic complications after infection

- more frequent in post-pneumococcal meningitis

mortality

- overall fatality rate is 15% in the US

- dependent on the causative organism and related to delay (>3 hrs) in ABX therapy

what are some of the risk factors of meningitis (long list!)?

- chronic medical disorders (CKD, DM, CF, etc.)

- extremes of age (<1 or >65 yo)

- under-vaccination (specifically for meningococcal or HIB vax.)

- immunosuppressed states (steroids, chemo, HIV, transplant)

- malignancy

- asplenia and sickle cell disease (which can cause 'functional asplenia' due to blockage of blood flow)

- living in crowded conditions

- travel to endemic areas (SW or NE US, Sub-Saharan Africa)

- alcohol use disorder

- bacterial endocarditis and IV drug use

- presence of ventriculoperitoneal shunt

- neurotrauma

- dural defects

- close/lengthy contact with someone with meningococcal disease

what are the 3 meningeal layers of the brain?

- dura mater (attached to skull)

- arachnoid

CSF is housed in the subarachnoid space

- pia mater (direct contact with brain parenchyma)

what's the difference between meningitis, encephalitis, myelitis, and encephalomyelitis?

- meningitis: infection of the meninges; inflammation of the pia mater, arachnoid, and CSF-filled subarachnoid space

- encephalitis: infection of the brain parenchyma

- myelitis: infection of the spinal cord

- encephalomyelitis: infection of the brain AND spinal cord

what type of barrier is the blood brain barrier (BBB)? describe its function

structural AND biochemical barrier

- non-fenestrated capillaries prevent passive diffusion from the intravascular space into the brain parenchyma

- limit host defenses in the CNS → complement and Ig levels are lower in the CSF than in serum!

during inflammation, permeability of the BBB is _____________

increased

- but the host defenses are still too low to fight the infection

what are the 3 methods of bacterial spread into the CNS?

hematogenous, contiguous, and nosocomial

what is hematogenous spread?

spreading via the bloodstream

- bacteria attach to the nasopharyngeal epithelium, breach the mucosal barrier, and gain access to the bloodstream

what is contiguous spread?

spread from local infections

- secondary to infections such as otitis media, sinusitis, or mastoiditis

- secondary to direct invasion through trauma

what is nosocomial spread?

caused by contamination during surgery or LP

what are the common infectious viral and fungal causes of meningitis?

- viral: enterovirus, herpes virus, HIV

- fungi: cryptococcus

what are the common non-infectious causes of meningitis?

rare!

- drugs: NSAIDs, methotrexate

- systemic disease: sarcoidosis, lupus

- neoplastic disease

what are the most common bacterial causes of meningitis in a patient <1 month old?

- Streptococcus agalactiae

- gram-(-) enteric organisms (E. coli, Klebsiella, Enterobacter)

- Listeria monocytogenes

what are the most common bacterial causes of meningitis in a patient 3-23 months old?

- Streptococcus agalactiae

- Streptococcus pneumoniae

- Neisseria meningitidis

- Haemophilus influenzae

- E. coli

what are the most common bacterial causes of meningitis in a patient 2-50 years old?

- Streptococcus pneumoniae

- Neisseria meningitidis

what are the most common bacterial causes of meningitis in a patient >50 years old?

- Streptococcus pneumoniae

- Neisseria meningitidis

- gram-(-) enteric organisms (E. coli, Klebsiella, Enterobacter)

- Listeria monocytogenes

what are the most common bacterial causes of meningitis in a patient with risk factors present (alcoholism, immunocompromised)?

- Streptococcus pneumoniae

- Listeria monocytogenes

- Haemophilus influenzae

what are the most common bacterial causes of meningitis in a patient post-neurosurgery (any age)?

- aerobic gram-(-) bacilli (Pseudomonas)

- Staphylococcus aureus

- coagulase-(-) staphylococci

what are the most likely pathogens, onset of Sx, and presentation of acute meningitis?

- likely pathogens: bacterial, viral

- onset of Sx: hours-days

- presentation: fever, chills, severe HA, nuchal rigidity (neck stiffness), AMS, photophobia, vomiting

what are the most likely pathogens, onset of Sx, and presentation of subacute or chronic meningitis?

- likely pathogens: TB, crytococcus, non-infectious

- onset of Sx: weeks-years (gradual)

- presentation: low fever, HA, lethargy, disability

what are the 4 primary signs of acute meningitis is adults?

- fever

- nuchal rigidity

- AMS

- severe HA

other than the 4 key signs of acute meningitis in adults, what are some other signs/Sx that you may observe?

- chills

- vomiting

- photophobia

- purpuric and petechial rash (meningococcal or H. influenzae)

what are the 2 physical assessments that may suggest acute meningitis in adults?

- Brudzinski's sign: flexion of the neck induces flexion of the knees

- Kernig's sign: stiffness of the hamstrings causes an inability to straighten the leg when the hip is flexed to 90 degrees

what are signs of acute meningitis in young children?

- bulging fontanelle (if not yet fused)

- apnea

- purpuric rash

- irritability

- refusal to eat

- convulsions

FYI - signs of a brain abscess depend on...?

size and location

- similar to other space-occupying lesions

FYI - what are the specific and non-specific signs of a brain abscess?

specific

- focal neurological deficits

- motor speech disorder

- ataxia

- seizures

non-specific

- HA

- fever

- nystagmus

- vomiting

what are the specific and non-specific signs of infective encephalitis?

specific

- AMS

- severe HA

- seizures

non-specific

- fever

- N/V

what are the primary physical assessment techniques used to identify meningitis?

determine the presence of meningeal irritation; reflect resistance to painful stretching of inflamed meninges from the lumbar level to the head

- Brudzinski's sign

- Kernig's sign

when would you seek cranial imaging to support a diagnosis of meningitis?

- moderately or severely impaired LOC

- new-onset seizures

- signs/Sx of brain abscess

- age >60 yo

- immunocompromised

what 3 tests should be performed to diagnose bacterial meningitis?

- CBC (leukocytosis)

- blood cultures

- lumbar puncture (spinal tap)

if a patient has bacterial meningitis, what would be observed upon visual inspection and lab testing of their CSF?

- CSF is cloudy, purulent (healthy CSF is clear!)

- increased WBC and PMNs (1000-5000 WBC/mm³, 80-95% PMNs)

- increased protein (100-500mg/dl)

- decreased glucose (<40 mg/dl, CSF to serum glucose ratio is ≤ 0.4)

- bacterial gram stain and culture positive (70-85% of the time)

- perform PCR for certain organisms!

what are the potential complications of a LP?

HA, local bleeding ("traumatic tap"), and brain herniation

how common are HAs as a complication of LPs?

10-25%

- likely due to low CSF pressure when the patient stands, caused by continued leakage of CSF at the lumbar site

how common is local bleeding as a complication of LPs?

20%

- rarely harms patient

- caused by hitting the venous plexus

describe brain herniation as a complication of LPs

- may occur in patients with increased ICP that transiently drops after LP

- patients are at risk for having CNS mass predisposed

- perform a CT/MRI for at-risk patients!

list the color, WBC count, differential, glucose levels, and protein levels in a patient with a normal CSF result

- color: clear, colorless

- WBC count (cells/mm³): <5

- differential: monocytes predominate

- glucose (mg/dl): 45-80

- protein (mg/dl): <50

list the color, WBC count, differential, glucose levels, and protein levels in a patient with bacterial meningitis

- color: cloudy

- WBC count (cells/mm³): elevated (1000-5000)

- differential: PMNs predominate

- glucose (mg/dl): decreased

- protein (mg/dl): elevated

list the color, WBC count, differential, glucose levels, and protein levels in a patient with viral meningitis

- color: cloudy

- WBC count (cells/mm³): elevated (50-1000)

- differential: lymphocytes predominate

- glucose (mg/dl): normal

- protein (mg/dl): slightly elevated

list the color, WBC count, differential, glucose levels, and protein levels in a patient with fungal meningitis

- color: cloudy

- WBC count (cells/mm³): normal to elevated (20-500)

- differential: lymphocytes predominate

- glucose (mg/dl): normal to decreased

- protein (mg/dl): elevated

list the color, WBC count, differential, glucose levels, and protein levels in a patient with TB meningitis

- color: cloudy

- WBC count (cells/mm³): normal to elevated (25-500)

- differential: lymphocytes predominate

- glucose (mg/dl): decreased

- protein (mg/dl): elevated

what are the common community-acquired organisms that cause meningitis?

- S. pneumoniae (gram-(+) cocci in pair/chains)

- H. influenzae (gram-(-) coccobacilli)

- N. meningitidis (gram-(-) diplococci)

- S. agalactiae (gram-(+) cocci in pair/chains)

- L. monocytogenes (gram-(+) bacilli)

- Enterobacterales (gram-(-) bacilli)

what are the common nosocomial or HC-acquired organisms that cause meningitis?

- P. aeruginosa (gram-(-) bacilli)

- S. aureus (gram-(+) cocci in clusters)