Encephalitis refers to inflammatory diseases of the brain parenchyma, including infectious inflammation as well as non-infectious inflammation. Among the infectious inflammatory diseases, which are caused by the invasion of pathogenic microorganisms into the central nervous system, microorganisms include viruses, bacteria, fungi, spirochetes, prions, parasites, etc. The most common is viral encephalitis, with herpes simplex virus encephalitis being the most common; bacterial encephalitis is most common with septic bacteria, diplococcus meningitidis, etc., and also includes special bacteria, Mycobacterium tuberculosis; spirochetes are most common with syphilis spirochetes. Non-infectious encephalitis is caused by immune abnormalities and is represented by autoimmune encephalitis, as well as multiple sclerosis (MS) and optic neuromyelitis optica, which can also involve the white matter of the brain.