How is encephalitis caused?

Written by Tang Li Li
Neurology
Updated on September 13, 2024
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Encephalitis generally falls into two categories: one is infectious inflammation caused by pathogenic infections, and the other is immune inflammation caused by abnormalities in immune mechanisms. Among these, the infectious type is the most common, including viral encephalitis, viral meningitis, tuberculous meningoencephalitis, purulent meningitis, and cryptococcal meningitis, which are associated with infections by viruses, bacteria, Mycobacterium tuberculosis, and Cryptococcus, respectively. Additionally, abnormalities in the immune system often cause autoimmune encephalitis, as well as multiple sclerosis and neuromyelitis optica when involving the brain, and acute disseminated encephalomyelitis, all of which are types of autoimmune encephalitis. The treatment approaches for these two types of encephalitis are different. For pathogen-induced cases, treatment primarily targets the pathogens: antiviral drugs for viral encephalitis, antibiotics for bacterial encephalitis, anti-tubercular therapy involving multiple drugs for Mycobacterium tuberculosis infection, and antifungal drugs, such as amphotericin B, for cryptococcal meningitis. For immune-mediated encephalitis, treatments generally involve immunosuppressants, high-dose corticosteroids, or intravenous immunoglobulins.

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Is encephalitis serious?

The severity of encephalitis varies greatly among individuals. Some mild cases of encephalitis, even with some degree of self-healing, do not require special treatment. For example, encephalitis caused by some enteroviruses and respiratory viruses has a very good recovery, and it is only necessary to prevent complications. However, some types of encephalitis are very dangerous and can even threaten the life of the patient. For instance, herpes simplex virus encephalitis can cause necrosis of the cerebral cortex, leading to high fever, headache, nausea, vomiting, and even epileptic seizures, psychiatric symptoms, and a significant increase in intracranial pressure, requiring urgent treatment.

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How is encephalitis caused?

Encephalitis generally occurs when pathogens invade the central nervous system of the brain, resulting in corresponding clinical manifestations. Patients may exhibit symptoms such as headache, fever, nausea, vomiting, and even paralysis of limbs and cognitive impairments. Patients become confused, with reduced computational and comprehension abilities. Some may also exhibit psychiatric symptoms and even experience seizures and other manifestations of epilepsy. Encephalitis is caused by pathogens, commonly viruses. Viral infections that lead to what is known as viral encephalitis can spread through the bloodstream to the brain and cause illness. Additionally, bacterial infections can also cause encephalitis. There are mainly two routes for bacterial infections: one is through bloodstream transmission leading to inflammation of the nervous system, and the other can occur directly, for example, from inflammation of the mastoids, tonsils, or cavernous sinus, where bacteria directly invade the brain, leading to the respective clinical manifestations. Furthermore, tuberculosis can also infect and cause tuberculous encephalitis, meningitis, and similar conditions.

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Symptoms of encephalitis vomiting

Patients with encephalitis often experience vomiting, and some even have projectile vomiting. This is mainly because patients with encephalitis experience a significant increase in intracranial pressure, which leads to severe vomiting. Additionally, patients may also have noticeable fever, headaches, and can display swelling of the optic disc. In such cases, it is necessary to promptly administer sufficient antiviral medications to the patient, as well as some medications to dehydrate and reduce intracranial pressure. If necessary, corticosteroids can also be used as an adjunct treatment. With aggressive treatment, some patients do recover well. (Please administer medication under the guidance of a professional physician.)

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What tests are conducted for encephalitis?

First, it is generally necessary to conduct an EEG test. This test is very convenient and non-invasive for patients. If significant slow waves are detected, encephalitis cannot be ruled out. Secondly, an MRI of the brain should be performed. If the viral encephalitis is severe, abnormal signals can be observed in areas such as the frontal lobe, temporal lobe, and hippocampus on the MRI, which are of great diagnostic reference value. Thirdly, lumbar puncture is also very important. It allows for a direct observation of the color of the cerebrospinal fluid, to monitor the pressure of the brain fluid, and to test the cerebrospinal fluid for cell count, protein, sugar, and chloride levels. These tests are very important for the diagnosis and differential diagnosis of encephalitis.

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Viral encephalitis and bacterial encephalitis differences

There are significant differences between viral encephalitis and bacterial encephalitis in clinical settings. Firstly, their clinical symptoms differ; the fever in viral encephalitis is generally lower than that in bacterial encephalitis, where there may be widespread chills and persistent high fever. From another perspective, laboratory tests also help differentiate the two. In viral encephalitis, a routine blood test shows no increase in white blood cells, mainly an increase in the proportion of lymphocytes. In contrast, bacterial encephalitis is characterized by a significant increase in white blood cells, which aids in distinguishing the two. Furthermore, an essential diagnostic tool is the lumbar puncture, through which cerebrospinal fluid can be tested. In viral encephalitis, the white blood cell count in the cerebrospinal fluid is slightly increased; in bacterial encephalitis, it is significantly increased. The cerebrospinal fluid in viral encephalitis has a slight increase in protein content with no significant change in chloride levels; however, in bacterial encephalitis, the protein content in the cerebrospinal fluid is notably higher, and there is a significant decrease in chloride levels.