Encephalitis is inflammation of the brain parenchyma and
occasionally spinal cord from infection, autoimmune conditions, or (in
rare cases) allergic reaction. Encephalitis is most commonly the result
of a viral infection, with the most common sporadic encephalitis cases
in the US caused by HSV (Greenlee, 2020). Direct viral invasion of the
brain usually damages neurons, and severe infections can cause
bleeding from the cerebral vasculature and haemorrhagic necrosis
(Greenlee, 2020). Given that the definition of health in almost every
case necessitates the relative absence of disease or infirmity, acute
infection or autoimmune response is directly contrary to the
definition of health.
Infectious encephalitis is defined as either primary or secondary.
Primary encephalitis results from direct infection of the brain or
spinal cord, where secondary infection begins elsewhere in the body
and then travels to the brain or spinal cord (Story, 2017).
Autoimmune encephalitis is subclassified either based on anatomic
location or the causative antibody (Farkas, 2021).
Encephalitis, especially from an infectious source, often begins with
generalized flu-like symptoms and malaise. Diplopia, photophobia,
and headache are often the first symptoms to appear, followed by
hallmark symptoms of encephalopathy: altered mental status
optionally with ataxia, tremor or myoclonus, and/or focal neurological
deficits. Bulging fontanelle can sometimes be found in infants.
Diagnostic tests include CSF analysis including opening pressures, cell
count, and culture; serum labs including blood culture, HIV serology,
and treponemal testing; imaging of the brain (MRI preferred to CT)
and chest (XR or CT); and EEG (Venkatesan & Geocadin, 2014). A
requirement for ruling-in encephalitis is altered mental status for 24
hours or greater. This must be accompanied by 2 or more of the
following that are not attributable to another cause or underlying
condition: documented fever within 72 hours, seizure, new focal
neurological findings, abnormal imaging of brain parenchyma
consistent with encephalitis, abnormal EEG, or presence of
leukocytes >= 5/mL in CSF (Venkatesan & Geocadin, 2014).
Story, L. (2017).
Pathophysiology: A Practical Approach
(3rd Edition). Jones & Bartlett
Learning. https://mbsdirect.vitalsource.com/books/9781284142983
Farkas, J. (2021, May 21).
Autoimmune Encephalitis
. EMCrit Project.
https://emcrit.org/ibcc/ae/
Greenlee, J. E. (2020, July).
Encephalitis - Neurologic Disorders
. Merck Manuals Professional
Edition. https://www.merckmanuals.com/professional/neurologic-disorders/brain-
infections/encephalitis
Venkatesan, A., & Geocadin, R. G. (2014). Diagnosis and management of acute encephalitis: A
practical approach.
Neurology: Clinical Practice
,
4
(3), 206–215.
https://doi.org/10.1212/cpj.0000000000000036
