An overview of the relevant aspects of the epidemiology, clinical presentation, basic disease mechanisms, diagnostic approaches and treatment options of the most common neurological diseases.
Module 6 Part 2: Encephalitis
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Do curso por University of California, San Francisco
Introdução à Neurologia Clínica
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Altered Mental Status, Brain Death, & Central Nervous System Infections
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Daniel Lowenstein, MDProfessor and Vice Chair, Department of Neurology
School of Medicine
S. Andrew Josephson, MDAssociate Professor
School of Medicine
Wade Smith, MDProfessor
School of Medicine
All right, let's move onto module number two, where we'll talk about Encephalitis.
So, the first thing to note is the
definition of encephalitis and how differs from Meningitis.
And basically, encephalitis, as opposed to meningitis,
implies that there's focal or global cerebral dysfunction.
And this can range from things like altered mental
status, language dysfunction, personality change,
altered behavior, memory problems or
specific motor and sensory deficits.
As with, meningitis, there can be inflammation of the leptomeninges,
but it sort of specifically implies inflammation within the brain parenchyma.
And note that the definition does not imply an infectious ideology.
There could be mul-, there are various etiologies for encephalitis.
One point of confusion is that acute
bacterial meningitis would sort of fit this definition.
And in fact many people refer to acute
bacterial meningitis as acute medic, bacterial meningo encephalitis.
But because of how it's described in literature, the
term meningitis is often used
interchangeably with bacteria path, pathogens.
And encephalitis has a different differential
diagnosis, where we're often not thinking about acute
bacteria, as we talked about in the previous module.
Given the variet, variety of etiologies, encephalitis itself can have a broad
array of presentations with patients presenting
with more subtle findings or sub-acute findings.
And patients presenting very acutely with very dramatic symptoms.
In addition, there are of a wide net of variety of pathogens many
of which are not always necessarily found
in terms of why patients have encephalitis.
And so the worldwide incidents of
encephalitis is difficult to quantify.
In this module, we'll spend a little
bit more time talking specifically about viral etiologies
as this is probably one of the more common causes of primary enceph of encephalitis.
And it's important to note that viruses can create both primary encephalitis via
viral invasion of the central nervous system
or a post infectious immune mediated encephalitis.
In which patients
have a more general viral syndrome such as an upper respiratory infection.
And then days to weeks later develop a encephalitis picture that we
think is more related to immune activation rather than direct viral pathogens.
There's no specific presenting symptoms to
help you make the diagnosis of encephalitis.
As we said before, there's a wide array of symptoms.
Patients can present with mild confusion or can present with coma.
They often present with seizures and focal neurologic symptoms.
In assessing patients with encephalitis, it's important to ask
about things like recent exposures, travel as well as vaccination.
To give you some examples,
arboviruses are more common during the mosquito season.
So it's helpful to know, you know, where patients have been, where they've
been, may have been exposed to mosquitoes and also the time of year.
Rabies, encephalitis is a uncommon form of encephalitis.
But, is often associated or usually is associated with animal bites.
So, getting that history is very helpful.
There might be certain types of encephalitities
that are more common in your area, for whatever reason, during
that particular time of year or some unusual association has just developed.
So knowing about what's prevalent in your
area is very helpful, and then knowing about
just general exposures to other types of animals
because they're often intermediate host of these pathogens.
As with the clinical features, the
examination doesn't typically have any classic findings.
again, it depends on what symptoms the patient presents with.
Some things that can be helpful would be general examination for viral exanthema.
Especially skin rash and so, doing a good dermatologic
evaluation, looking for things like grouped vesicles within a dermatome.
Which would be
suggestive of varicella zoster infection and could
suggest a underlying vis a vis encephalitis.
In populations that are not being vaccinated for mumps.
Patients that present with parotitis.
Usually think about mumps encephalitis. Flaccid paralysis is classically
seen with some of the arbovirus mediated encephalitites including West Nile virus.
Which is becoming more and more prevalent in the United States.
And then, s, specific symptoms, like hydrophobia
and aerophobia can be associated with rabies encephalitities.
Making the diagnosis involves, using a lot
of your, sort of, neurology diagnostic tools.
A lumbar puncture is a hallmark of making the diagnosis and
should show elevated, white blood cell
counts, usually with the lymphcyte predominance.
There often as elevated protein, and normal
glucose levels in contrast to acute bacterial meningitis.
Depending on the cause of encephalitis,
you may not, not necessarily see elevated white cells especially
if the, clinical presentation is delayed for any period of time.
But with most viral etiologies, you will see that.
Imaging and electroencephalography or EEG, are often
abnormal, but there are again no specific pattern.
EEG may show focal seizures or focal areas of dysfunction.
And often
the specific diagnosis is made by testing for a specific pathogen, such as a
specific viral DNA sequence or antibodies to,
to viral pathogens either from serum or CSF.
We'll take some time to talk a little bit more in detail about herpes simplex
virus encephalitites or encephalitis because it's the
most common cause of sporadic fatal encephalitis worldwide.
And so it's an important one to recognize, because it
has a specific treatment, and has a fairly high mortality.
It has a predilection to involve the temporal lobes and so EEG
often shows focal discharges over these areas and imaging also tends to show
abnormalities within temporal lobes. And this can include hyper-intensity
on MRI or hypo-density on CT as well has hemorrhage and the
diagnoses is made by testing for HSV or herpes DNA from the CSF.
Or whether the patient responds to empiric antiviral treatment.
This is a slide showing an MRI scan from a patient with herpes enceph, encephalitis.
It's a MRI showing three coronal images back to
back um,sort of through space and this is a flare sequence.
And you can see that there's some hyper intensity, within the left temporal lobe.
Seeing that sort of asymmetric pattern of injury in the right clinical context
should alert you that herpes encephalitis is a possible culprit in this case.
Herpes encephalitis is treated with high dose Acyclovir.
Usually ten to 15 milligrams per kilogram IV for two to three weeks.
And treatment is very important because without treatment
the mortality of this disorder reaches about 70%.
Even with treatments there still is a relatively high mortality of 20 to 30%.
And just as we saw with acute
bacterial meningitis the survivors often have significant neurologic
complications including epilepsy amnesia and
memory disturbance, personality and behavioral change.
And that's probably due again to the predilection to
the temporal lobe and the structures in those areas.
We talked a little bit about different type
of viral encephalitis and there's both direct encephaliti,
enfi, sorry direct viral disease or invasion of
the brain parenchyma as we saw with herpes.
But, also you can develop a post infectious encephalitis.
And a couple examples of that, I'll highlight here.
One is acute disseminated
encephalomyelitis, often abbreviated as ADEM.
And this is a widespread demyelinat
injury to the central nervous system that is more common in children.
And often follows a systemic viral
syndrome such as an upper respiratory infection.
There have been case reports in particular with Epstein-Barr
virus, but it's been associated with multiple different viral illnesses.
And this is treated with steroids and it's usually a monophasic illness.
Another example
which behaves a little bit differently, is subacute sclerosing panencephalitis.
And this a progressive neurodegenerative condition associated with
periodic myoclonus, that follows a primary measles infection.
And, and interesting about SSPE is that this
disorder can develop years after the primary measles infection.
Cerebral vasculopathy and arteriopathy leading to stroke
is a common complication of VZV infection.
So a young person in particular presenting with
a stroke should have a thorough history in
terms of things like chicken pox or other
signs of Zoster infection, preceding the acute stroke.
This is an MRI scan again showing flare
sequences now for an axial view of a patient
with diffuse demyelinating disease as you see these white
matter lesions, and this is an example of ADEM.
Aseptic meningitis, is an important topic to discuss here because many
of the pathogens that cause viral
encephalitis can also cause aseptic meningitis.
Aseptic meningitis is a little bit of a confusing term, and it's defined
as meningeal inflammation, that is elevated
CSF white count, with negative bacterial cultures.
So, despite the term aseptic, it doesn't
necessarily imply that there's not an infectious etiology.
It just means that the cultures from CSF do not grow bacteria.
In addition these patients don't show signs of brain parenchymal injury.
And so they present with headache, fever, stiff neck.
But usually have a self-limited course that.
And their symptoms get better, over days to weeks without any specific treatment.
And because of this, we often don't find a specific etiology, for their meningitis.
A
couple points in, with relation to aseptic meningitis,
enterovirus is probably the most common viral pathogen.
And again, causes a self limited course, acute HIV infection can cause aseptic
meningitis, so in the appropriate patients,
it, it's important to screen for this.
HSV Type 2 can cause recurrent meningitis, without encephalitis.
A typical bacteria
including spirochetes, such as syphilis, can cause an aseptic meningitis, and these
are important to, to also think about, because they do respond to antibiotics.
And then it's also an important thing to consider in
patients with sort of chronic meningitis including fungal and parasitic infections.
Which are often associated with eosinophils in
the CSF as well as neoplastic meningitis.
And in the latter two cases often
the patients develop clear neurologic
symptoms as the inflammatory process progresses.
So, in summary for this module, we spent some times defining encephalitis as well
as aseptic meningitis and distinguishing it from
acute bacterial meningitis in module number one.
We talked a little bit about thinking about,
common pathogens for encephalitis.
Realizing that sometimes a viral pathogen can cause
direct infection encephalitis versus a post infectious phenomenon.
We spent a little bit of time talking about HSV encephalitis.
In particular, given a time mortality and morbidity.
And then we also highlighted the importance of
doing a thorough travel history and exposure history.
As you're trying to figure out what type
of pathogen may have contributed to this patient's presentation.
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