Encephalitis

• Can be viral, bacterial, fungal, or parasitic

• If there are abscesses it’s usually due to bacteria

• Viral encephalitis

  • CMV and herpes are the 2 most common causes

  • Arboviruses (arthropod borne) can also cause encephalitis

    • Transmitted by biting insects

    • Local outbreaks associated with mosquitoes (birds are reservoirs)

    • Viruses: St. Louis, Eastern equine, Western equine, Venezualan equine, California, Japanese, and West Nile virus

  • Mumps, measles, rubella, and chickenpox can cause encephalitis

  • Herpes encephalitis

    • Most common cause of viral encephalitis

    • HSV-1 causes an acute encephalitis that usually involves the temporal lobes

    • HSV-2 is a problem in babies born to infected moms; can cause meningitis in older persons

    • Can occur without active infection elsewhere

  • CMV

    • Seen in the immunocompromised and fetuses

    • Starts as ependymitis and spreads through the CSF

    • Can cause focal, necrotizing lesions of brain tissue that may lead to periventricular calcification

    • Also causes meningitis and spinal radiculitis

  • Poliomyelitis

    • An enterovirus that secondarily involves nervous tissue

    • Initially a meningitis

    • Involvement of only anterior horn motor neurons; produces a flaccid paralysis (death by respiratory paralysis or myocarditis)

    • Pretty much gone now due to vaccine

  • Rabies

    • If untreated, causes a fulminant encephalitis that is always fatal

    • M/O get to CNS by peripheral nerves

    • See local paresthesias at site of wound and malaise, H/A, and F (classic)

    • Selectively involves basal cerebral nuclei, midbrain, and floor of 4^th ventricle

    • Negri bodies: intracytoplasmic inclusions of virion aggregates

    • 2 forms

      • Furious: volatile, violent, emotional behavior with lucid states and hydrophobia; usually die from arrhythmias

      • Paralytic (dumb): ascending flaccid paralysis; die of respiratory arrest

  • Subacute sclerosing panencephalitis

    • Kids and young adults who had measles

    • Personality change followed by involuntary movements; progressive over years

    • Defective viral particles lack M protein of viral coat and spread more slowly

Category: Pathology Notes