Encephalitis: Introduction and Symptoms

00:00 So let's talk about encephalitis. What is encephalitis? Encephalitis is diffuse inflammation of the brain parenchyma, that outer cortical surface. The subarachnoid space and the pia, the pia goes in to all areas of the cortical surface of the brain down into the sulci and overlapping all of the brain parenchyma. Sometimes encephalitis can be associated with a meningitis and we call that meningoencephalitis and sometimes encephalitis can be associated with a focal infection of the brain and we call that an encephalocerebritis. What are the etiologies? What causes encephalitis? What causes a generalized brain infection? Well some of the common organisms we see are herpes simplex virus 1 more than 2, we'll talk about the difference. St. Louis encephalitis, West Nile virus, eastern equine and western equine encephalitis and then other viruses like varicella zoster, Epstein-Barr, and cytomegalovirus.

01:01 How do patients present? What are the signs? What are the symptoms that tip us off to say this is an encephalitis? The most common cause of an encephalitis is a virus so we often see a viral prodrome. Two weeks or several weeks or more than several days of headache, malaise, maybe myalgias, elevated liver enzymes, a viral prodrome. This typically culminates in global neurologic deficit, not often a focal deficit but global dysfunction. Patients are drowsy and fatigued, they may have seizures or tremors. Memory complaints are common particularly with herpes encephalitis. Personality changes may occur, hallucinations may happen, vision problems may occur. Think of all those lobes of the brain, all those areas and many can become dysfunctional and cause global neurologic deficit. As the disease progresses over hours to typically days or weeks, we see other symptoms. Patients may culminate with a classic triad of headache, fever, and altered mental status which can range from delirium, disorientation to confusion or patients may ultimately present with a new focal neurologic deficit that is often a late presenting finding, hemiparesis, aphasia, cranial nerve deficits, and even seizure.

02:15 Let's talk about some typical causes and presentations of encephalitis and let's focus on this example of a herpes encephalitis. This is a common cause of encephalitis and is a frequently tested cause of encephalitis and something that you and we should know. HSV encephalitis or herpes encephalitis is mostly caused by HSV-1, but we see HSV-2 in neonates as a result of maternal transmission. The typical clinical presentation again can be the classic triad of headache, fever, and altered mental status. Patients often present with that viral prodrome of malaise, maybe memory impairments or personality changes. Memory impairment and visual field defects can be present, can occur. And there are 2 presentations that we tend to see with a herpes encephalitis. The first is more severe, there is rapid progression to coma and death often within weeks and this may be seen without treatment and in some cases even with treatment. There is also a more indolent form of this viral infection that can occur with hallucinations and headache, prominent memory dysfunction because HSV typically affects the temporal lobes where we form new memories in the hippocampus, and behavioral disturbances.