Examination If<unk>  is suspected, then questions can be asked about the individual's history and physical examination can be performed. Important aspects of one's history include immune status, exposure to animals, including insects, travel history, vaccination history, geography, and time of year. Symptoms usually occur acutely, and the most common symptoms of infection are fever, headache, altered mental status, sensitivity to light, stiff neck and back, vomiting, confusion, and, in severe cases, seizures, paralysis, and coma. Neuropsychiatric features such as behavioral changes, hallucinations, or cognitive decline are frequent. Severe symptoms are most common among infants and the elderly. Most infections are asymptomatic, lacking symptoms, whereas most symptomatic cases are mild illnesses. Virus-specific symptoms may also exist or tests may indicate one virus. Specific examples include: * Enterovirus 71 may cause tremors, twitching, impaired balance and coordination, fluid accumulation in the lungs, and cranial nerve palsies. * Epstein-Barr virus encephalitis is usually accompanied by enlargement of the lymph nodes and enlargement of the spleen * Herpes zoster encephalitis may be accompanied by rash and skin vesicles, and because it involves the frontal lobe and temporal lobe, is often characterized by psychiatric features, memory deficits, and loss of language faculties. * Many arboviral encephalitides, such as Japanese encephalitis, primarily affect the basal ganglia, sometimes causing motor symptoms such as involuntary movements and movements similar to those observed in Parkinson's disease. * Nipah virus may produce brainstem and cerebellar signs, hypertension, and segmental myoclonus, or twitching of a group of connected muscles. * Zika virus characteristically may cause microcephaly among newborn children if a pregnant woman is infected. Histology The brain histology of<unk>  shows dead neurons with nuclear dissolution and elevated eosinophil count, called hypereosinophilia, within cells' cytoplasm when viewed with an optical microscope. Because encephalitis is an inflammatory response, inflammatory cells situated near blood vessels, such as microglia, macrophages, and lymphocytes, are visible. Virions within neurons are visible via electron microscopes. Clinical evaluation + Preferred diagnostic test according to suspected etiology. Virus Preferred diagnostic test Cytomegalovirus CSF PCR or CSF-specific IgM Dengue/Chikungunya/Zika CSF PCR or CSF-specific IgM Enterovirus Stool and throat PCR are preferred over CSF PCR Epstein-Barr virus Serum EBV capsid antigen IgG and IgM (VCA) and EBV nuclear antigen IgG (EBNA) Herpes simplex virus CSF PCR, can be repeated within 2 to 7 days of disease onset if negative with high clinical suspicion; or CSF for HSV-IgG after 10–14 days of disease onset HHV-6 CSF PCR paired with serum PCR to exclude viral integration into host DNA that causes false positives Influenza Culture, antigen test, PCR of respiratory secretions Measles CSF-specific IgG Varicella-zoster virus CSF-specific IgG Neuroimaging and lumbar puncture (LP) are both essential methods of diagnosing<unk> . Computed tomography (CT) or magnetic resonance imaging (MRI) help identify increased intracranial pressure and the risk of uncal herniation before performing an LP. Cerebrospinal fluid (CSF), if analyzed, should be analyzed for opening pressure, cell counts, glucose, protein, and IgG and IgM antibodies. CSF testing should also include polymerase chain reaction (PCR) testing for herpes simplex viruses 1 and 2 and enteroviruses. About 10% of patients have normal CSF results. Additional testing, such as serology for various arboviruses and HIV testing, may also be performed based on the individual's history and symptoms. Brain biopsy and body fluid specimen cultures and PCR may also be useful in some cases. Electroencephalography (EEG) is abnormal in more than 80% of<unk>  cases, including those who are experiencing seizures, and may need to be monitored continuously to identify non-convulsive status. Lack of testing resources may prevent accurate diagnosis. Test results specific to certain viruses include: * For herpes simplex virus encephalitis, a CT scan may show low-density lesions in the temporal lobe. These lesions usually appear 3 to 5 days after the start of the infection. * Japanese encephalitis often has distinct EEG patterns, including diffuse delta activity with spikes, diffuse continuous delta activity, and alpha coma activity. Differential diagnosis A broad differential diagnosis can be performed that looks at many potential causes of the encephalitis, infectious and noninfectious. Potential alternatives to<unk>  include malignancy, autoimmune or paraneoplastic diseases such as anti-NMDA receptor encephalitis, a brain abscess, tuberculosis or drug-induced delirium, exposure to certain drugs or toxins, neurosyphilis, vascular disease, metabolic disease, or encephalitis from infection caused by a bacterium, fungus, protozoan, or parasitic worm. In children, differential diagnosis may not be able to distinguish between<unk>  and immune-mediated inflammatory CNS diseases, such as acute disseminated encephalomyelitis, as well as immune-mediated encephalitis, so other diagnostic methods may need to be used.
Viral encephalitis
Anti-NMDA receptor encephalitis
Herpesviral encephalitis
Anti-Hu associated encephalitis
Powassan encephalitis
Autoimmune encephalitis
Fungal meningitis
Viral meningitis