clinmed2test3: Infections of the Central Nervous System ppt

Infections of the Central Nervous System (CNS)

• Infections of the CNS include meningitis, encephalitis, and brain abscesses.
• These infections cause CNS dysfunction by destroying brain tissue and increasing intracranial pressure.

Types of CNS Infections

• Meningitis: acute inflammation of the leptomeninges (pia and arachnoid mater) caused by microbial infection growing within the CSF.
• Encephalitis: inflammation of brain parenchyma.
• Brain Abscess: localized collection of pus within the brain parenchyma.

Acute Bacterial Meningitis

• Etiology:
  • Neonates: Group B Strep, Listeria, enteric gram-negative rods.
  • Children: S. pneumoniae, N. meningitidis, H. influenzae.
  • Adults: S. pneumoniae, N. meningitidis.
• Clinical correlations:
  • Classic triad of fever, stiff neck, and altered mental status has a low sensitivity (44%) for bacterial meningitis.
  • Meningeal inflammation causes stiff neck, headache.
  • "Toxins" cause brain swelling, increased ICP, herniation, encephalopathy, and seizures.
  • Inflammation of cranial nerve causes nerve palsies.
  • Vasculitis/Thrombosis causes brain infarcts.
  • Meningeal fibrosis causes communicating hydrocephalus.
• Onset within 24 hours in ~90% of patients.
• Bacterial meningitis is a medical emergency with near 100% mortality without treatment.

Lumbar Puncture (LP)

• Performed between 3rd and 4th lumbar vertebra.
• CSF analysis in meningitis:
  • Elevated pressure and turbidity indicate bacterial infection.
  • Clear and normal pressure indicate viral infection.
  • Fungal infection: clear and normal-elevated pressure.

Antibiotic Therapy

• Empiric antibiotic therapy: third-generation cephalosporin (e.g. ceftriaxone) and vancomycin.
• Start therapy immediately after collecting CSF vials.
• For adults with pneumococcal meningitis, dexamethasone 10 mg IV with the first dose of antibiotics and every 6 hours for 4 days decreases morbidity and mortality.

Subacute and Chronic Meningitis

• Presents with fever, headache, meningismus, and altered mental status similar to acute meningitis.
• More gradual onset over weeks to months.
• Organisms associated with subacute/chronic meningitis include mycobacteria (TB), fungi (cryptococcosis), and spirochetes (syphilis, Lyme disease); sarcoidosis can be chronic.
• An important cause of subacute or chronic meningitis is not-fully-treated acute meningitis.

Tubercular Meningitis

• Granulomatous inflammation, mainly involving the base of the brain.
• Brain infarcts from vessel involvement.
• Cranial nerve deficits from nerve damage.
• Meningeal fibrosis can cause hydrocephalus.

Cryptococcosis

• Caused by Cryptococcus neoformans, a spherical, budding yeast with a thick polysaccharide capsule.
• Present in soil, bird excreta.
• Common cause of infection in immunocompromised patients.

Aseptic Meningitis

• Caused principally by viruses, especially herpes simplex virus and enteroviruses.
• Has a more benign and self-limited course.
• Can occur with secondary syphilis and disseminated Lyme disease.
• Prior to the routine administration of MMR vaccines, mumps was the most common cause of viral meningitis.
• Drug-induced aseptic meningitis has been reported with NSAIDs, sulfonamides, and certain monoclonal antibodies.

Encephalitis

• HSV 1 encephalitis is the most common viral encephalitis.
• Very destructive, causing necrosis and hemorrhage in the brain, typically in the temporal lobe.
• HSV encephalitis requires effective treatment.
• Start all patients with suspected encephalitis on acyclovir.
• When started early, acyclovir has been shown to significantly decrease mortality and morbidity and limit long-term behavioral and cognitive impairment.

Brain Abscesses

• Presents as a space-occupying lesion.
• Symptoms may include vomiting, fever, altered mental status, or focal neurologic findings.
• CT without contrast scan of the brain should be performed.
• Bacteriology of brain abscess is usually polymicrobial and includes S. aureus, gram-negative bacilli, streptococci, and mouth anaerobes (MOUTH - dental care).
• 14-58% of cases develop from chronic otitis media.
• 55% form an abscess in the temporal lobe.
• Proteus mirabilis is the most common pathogen isolated in these brain abscesses.
• Can also develop after head trauma, systemic infection (pneumonia, endocarditis, tooth decay).
• Treatment: Surgery, I&D.