CNS Infections-Meningitis

Meningitis - Bacterial Infection of the Meninges (covering of the brain) and Cerebral Spinal Fluid (CSF).

Etiology of Meningitis
  • 0 to 3 Months: group B Streptoccus (GBS), E coli, Listeria, fungi, & anaerobes [Viral: HSV, CMV]
  • 3 months to 3 years: Neisseria meningitidis, S. pneumoniae, H. influenzae (reduced by 98% since 1991), [Viral: enteroviruses, HSV, human herpes 6] AFB
  • 3 to 21 years: N. meningitidis, S. pneumoniae [Viral: enteroviruses, arboviruses, and herpesviruses, EBV, herpes 6, influenza A & B] Mycoplasma pneumoniae
LUMBAR PUNCTURE (LP) is the most important test in the diagnosis of CNS infection. CSF findings LP are the Gold standard in the diagnosis of meningitis.

CSF findings with CNS Infections
  • Bacterial Meningitis
    • Glucose: low
    • Protein: normal to mild increase
    • Cell Count: polymorphonuclear cells(may have monos very early)
    • Other Studies: Positive Gram stain, Bacterial antigens
    • Culture positive for organism
  • Viral Meningitis and Encephalitis
    • Glucose: normal
    • Protein: increased
    • Cell Count: mononuclear cells (may have polys early)
    • Negative bacterial cultures
    • Occasional positive viral cultures
    • Positive PCR
    • Positive rise in serum antibodies
  • Fungal Meningitis
    • Glucose: low
    • Protein: high
    • Cell Count: monos
    • Other Studies: positive India ink
    • Positive fungal culture
    • Positive antigens (cryptococcal)
  • Tubercular Meningitis
    • Glucose: low
    • Protein: very high
    • Cell Count: high polys
    • Other Studies:AFB fluoro Ab, TB culture
Indications for Lumbar Puncture
  • Clinical suspicion of meningitis
  • Seizure with fever and less than 18 months of age
  • To obtain CSF for diagnosis of acute, sub-acute or chronic neurologic disease.
Contraindications for Lumbar Puncture
  • Herniation (posturing)
  • asymmetrical pupils
  • new hemiparesis
  • Brain Abscess or empyema
CT or MRI Imaging with Meningitis: to evaluate for subdural effusion, hydrocephalus, infarction (arterial or venous).

Clinical Indicationsfor Neuro-Imaging with CNS infection
  • Failure in decline of fever curve after 72 hours of treatment
  • Late, focal or persistent convulsions
  • focal neurologic signs
  • increasing head size
  • papilledema
  • Newborn
  • Relapse or recurrence
CNS Infections-Encephalitis

Encephalitis is a viral infection of the brain and meninges with an associated inflammatory response of the csf.

Arthropod born encephalitis is spead by insects and occurs in late spring and summer and includes Eastern Equine Encephalitis (EEE), Western Equine Encephalitis (WEE), Venezuelan Equine Encephalitis (VEE), St. Louis Encephalitis, and California Encephalitis. Non-arthropod encephalitis is caused by viruses that primarily infect other body tissues and have a secondary site of infection in the CNS. These my be seasonal since numerous viral invections are seasonal, i.e. Enterovirus, influenza, EBV, or may occur at any time of the year with non-seasonal infections, i.e. Herpes.

Symptoms of Encephalitis if occuring in setting of fever or progression of symptoms over hours to days
  • obtundation progressing to coma
  • speech and language disturbances (especially with Herpes)
  • seizures
  • agitation
  • hallucinations
Herpes has no seasonal preference. Suspect Herpes and start Acyclovir for suspected encephalitis if language or speech change is an early symptom, complex partial seizures, or fall and winter season.

CNS Infections-Brain Abscess

Brain Abscess is a collection of purulent and necrotic debris loculated in an area of brain. Brain abscess may by singular or multiple.

Clinical Signs of Brain Abscess
  • headache
  • change in sensorium (progressive obtundation, lethargy)
  • vomiting
  • fever
  • seizures
Presdisposing factors of Brain Abscess
  • contiguous suprative facus
    • esp: sinusitis in adolescent boys
    • otitis, less common
    • dental abscess
    • scalp infections
  • pulmonary infections (Cystic Fibrosis)
Organisms in Brain Abscess
  • mixed flora
  • Strep anerobes 60%-70%
  • Staph in penetrating trauma
Treatment Brain Abscess
  • broad spectrum antibiotics
  • surgery if large singular or empyema
  • steroids preoperatively after antibiotics