Encephalitis and Acute Disseminated Encephalomyelitis: Overview and Clinical Features

Encephalitis refers to inflammation of the brain’s parenchyma—the functional tissue composed of neurons and glial cells—primarily caused by direct invasion of infectious agents, most commonly viruses. This inflammation disrupts normal brain function and can lead to a wide spectrum of neurological symptoms. In contrast, acute disseminated encephalomyelitis (ADEM) is an inflammatory condition affecting both the brain and spinal cord. Unlike encephalitis, ADEM results from an autoimmune hypersensitivity reaction, where the immune system mistakenly attacks the central nervous system following exposure to a virus or another foreign protein, such as certain vaccines or infections.

Both encephalitis and ADEM may be triggered by numerous viral pathogens, including herpes simplex virus, varicella-zoster virus, enteroviruses, and arboviruses. The clinical presentation of these disorders typically includes fever and headache—reflecting systemic and central nervous system inflammation—along with altered mental status ranging from confusion to coma. Patients often experience seizures or focal neurological deficits such as weakness, sensory disturbances, or difficulty speaking, which correspond to localized brain involvement.

Confirming the diagnosis involves a combination of laboratory and imaging studies. Analysis of cerebrospinal fluid (CSF) obtained via lumbar puncture is essential to detect markers of inflammation, viral genetic material, or other signs suggestive of infection or immune activation. Neuroimaging, particularly magnetic resonance imaging (MRI), is invaluable for visualizing areas of inflammation, helping to differentiate between encephalitis and ADEM and to rule out other causes such as stroke or tumors.

Management of these conditions is largely supportive, aimed at controlling symptoms and preventing complications. When a specific viral cause is identified, antiviral medications such as acyclovir (commonly used for herpes simplex virus encephalitis) may be administered to limit viral replication and reduce brain injury. For ADEM, immunomodulatory treatments—including corticosteroids, intravenous immunoglobulin, or plasmapheresis—are often employed to suppress the aberrant immune response. Early diagnosis and treatment are critical to improve outcomes and minimize the risk of long-term neurological deficits.