Encephalitis: Diagnosis

00:02 Now, when somebody comes in with altered mental status and signs of encephalitis, we certainly are going to examine the cerebrospinal fluid if it's safe.

00:13 And so, what we’re going to look for is the cytology.

00:16 And what you would expect, unlike bacterial meningitis, is a lymphocytic pleocytosis.

00:24 There may be some neutrophils there, but there is a predominance of mononuclear cells.

00:30 Unlike bacterial meningitis, your glucose is normally not low.

00:38 The protein may be elevated.

00:42 Those are the classic findings, but the exceptions to the rule are the West Nile virus, which may have more neutrophils in it and Eastern equine encephalitis may have a neutrophil predominance.

00:57 And the cell count is going to be 50 to 500 cells.

01:03 To make a specific diagnosis, we have to rely on PCR and antibody studies.

01:10 The herpes simplex PCR is very sensitive and very specific and we use it all the time.

01:19 For varicella zoster, it's not nearly so sensitive, but it does have a high specificity.

01:25 Culturing these viruses is not particularly useful.

01:32 So, serology is important and we’re going to get an acute serum on admission and then periodically get convalescence serum, looking for antibody rises.

01:46 We can do PCR on gastrointestinal samples, respiratory secretions and skin vesicles and they're pretty sensitive and specific.

01:55 But if we just can't figure out why the patient has encephalitis and the patient is deteriorating, then we may need to resort to a brain biopsy.

02:07 These are usually done through a burr hole and a needle aspirate.

02:17 Neuroimaging is important in patients who have encephalitis and the MRI is the study of choice.

02:24 And particularly, in herpes simplex virus, 90% of the time you're going to be looking in the temporal lobes.

02:34 Varicella zoster produces multifocal hemorrhage and infarction and a West Nile virus has less frequent abnormalities than herpes simplex virus.

02:50 We don't do EEG very often, but if you were to do it, you'd find generalized slowing in most forms of encephalitis.

02:59 And in herpes, you’d find, once again, abnormalities like spikes in the temporal lobe.

03:07 And you’d find that in a majority of patients with herpes virus encephalitis.

03:14 And this, for example, is what herpes virus encephalitis looks like.

03:19 Notice the predominance in both temporal lobes in this patient.

03:25 Notice the multifocal location in the patient with varicella zoster encephalitis.

03:32 And notice that in West Nile virus, the encephalitis is highlighted by increased signal in the basal ganglia.

03:41 And remember, we talked about parkinsonism, and so that fits with West Nile virus.

03:50 The enteroviral encephalitis, you can have increased signal in both hemispheres.