Encephalitis

Question 1

What are some symptoms of encephalitis?

Answer 1

altered LOC, focal neurological deficits, seizures (moreso than in meningitis), coma, plus the usual symptoms you’d see with meningitis

Question 2

About 50% of encephalitis cases are idiopathic, but What are some of the most common known causes?

Answer 2

1. HSV 1 and 2 (about 25%)
2. Varicella zoster
3. Postinfectious from measles, mumbps, rubella, etc
4. Enteroviruses
5. Arboviruses (depending on geogrphay)
6. Rabies
7. Mumps, measles

Question 3

What are the steps in diagnosing encephalitis?

Answer 3

1. consider in any patient with altered LOC, unexplained fever, seizures or new focal neurological deficits
2. CT scan
3. LP if safe to do so

4, Test CSF for WBC, protein, glucose

5. Can undergo PCR or serologic testing

Question 4

What is the typical empirial drug of choice for viral encephalitis>

Answer 4

acyclovir

Question 5

HSV encephaltis most often affects what part of the cortex? How about flaviviruses?

Answer 5

HSV = temporal lobe

Flaviviruses = basal ganglia and thalamus

Question 6

What subtype of encephalitis is MRI crucial in diagnosing?

Answer 6

ADEM and othe rforms of postinfectious encephalitis

Question 7

What three herpes viruses are associated with encephalitis? What subgroup of herpesviruses do these fall under?

Answer 7

HSV 1, HSV2, and VZV

they are all alpha herpes viruses

Question 8

Where do alpha herpesviruses stay dormant?

Answer 8

neurons

Question 9

What are some general characteristics of the herpes viruses?

genome? structure? virulence?

Answer 9

THey are large, enveloped icosahedral viruses with large dsDNA genomes (class 1)

They encode many proteins that serve to modulate the host cell immune response

also encode for several proteins that are required to promote viral DNA replications

Can cause lytic, persistent, latent and sometimes immortalizing infections.

Question 10

Why is cell-mediated immunity essential for the control of herpes simplex infections?

Answer 10

they can create latent infections, so the infected cells need to be destroyed

Question 11

Is HSV1 or 2 more likely to cuase encephalitis? meningitis?

Answer 11

HSV 1 = encephaltis

HSV 2 - aseptic meningitis

Question 12

Although HSV and VZV are both herpes viruses, they cause encephalitis in slightly different ways. How?

Answer 12

HSV causes encephalitis when the reactivation of laten virus in neurons goes the “wrong direction” up to the CNS instead of tho the periphery.

In VZV, it’s during the viremia that the virus reaches the CNS - so it can be in either the primary infection or in a reactivation event

Question 13

How does acyclovir work?

Answer 13

It’s a bioprecusor prodrug that is converted to an active form by being phosphorylated by thymidine kinase.

Once it’s phosphorylated it looks like a nucleotide, but it lacks the 2’ hydroxyl needed for chain continuation, so it acts as a chain terminator - interferes with DNA and RNA synthesis

Question 14

What is postinfectious encephalitis and what form is most common?

Answer 14

It’s encephalitis caused by a viral infection (mumps, measles, rubella, varicella, influenza, etc)

Acute disseminated encephalomyelities (ADEM) is the most common

It’s basically inflammatory demyelination that occurs anywhere from days to 4 weeks post viral infection

Question 15

What are some characteristics of the measles virus? Genome, structure, etc.

Answer 15

• ssRNA (group V)

nonsegmented

helical nucleocapside

enveloped

Question 16

What is a genetic component in a patient’s ability to clear a measles infection withint deveoping encephalitis?

Answer 16

people who have genetic polymorphisms resulting in lower production of interferon alpha and interleukin 2 cannot mount an effective immune response, so they are more likely to develop neurological complications

Question 17

Wha thappens in primary measles encephalitis (PME)?

Answer 17

in 1-3 out of 1000 patients

the virus invades and repliates in brain cells at the same time as when the rash presents - fever, heaahce, mental status changes, motor deficits, seizures

Treatment is supportive and there is a 15% mortality rate and a 25% rate of lifeling neurological problems

Question 18

What happens in subacute sclerosing panencephalitis (SSPE)?

Answer 18

More rare (4-11 in 100,000)

usually children who contract measles before age of 2

They have acute infection which appears to resolve

symptoms free usually until their teen years

then they start to have behavioral problems, academic performance decline, the neurological dysfunction - all gradually worsen

Restulsf rom a “slow infection” of the brain where viral gene expression is reduced and defective viral particles build up and cause neuronal damage

usually die about 1-3 years after symptoms develop

Question 19

What is the treatment for acute disseminated encephalomyelitis (ADEM)?

Answer 19

Corticosteroids to dampen the immune response

Question 20

How does rabies lead to enterovirus?

Answer 20

1. virus inoculated through bite
2. virus replicates in muscle
3. Virion enters the peripheral nervous system
4. Passive ascent of virus via sensory fibers
5. replication in dorsal ganglion
6. rapid ascent in the spinal cord
7. infection of the spinal cord, brainstem, cerebellum
8. descending infection to eye, glands, skin an dother organs

Question 21

What animal most often spreads rabies here?

Answer 21

skunk

Question 22

What are some of the neurological symptoms you see in rabies encephalitis?

Answer 22

hydrophobia, pharyngeal spasms, hyperactivity, anxiety, depression, loss of coordination, paralysis, confusion, delerium

ultimately coma and death due to respiratory paralysis

Question 23

What is the treatment for rabies?

Answer 23

the patinet has ot be passively immunized with rabies immune globulin (RIG = human antibodies against rabies) injected both at the site of the bite and intramuscularly

also need to be immunized with an inactivated rabies virus preparation