Infectious and autoimmune encephalitis: causes, symptoms, diagnosis and treatments.
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Encephalitis is inflammation of the functional tissue, called parenchyma, of the brain. Inflammation causes the brain to swell, producing a variety of neurological symptoms. It is a very serious condition requiring immediate medical attention to reduce the risk of long-term complications or death.
Encephalitis can result from brain infections, or autoimmune reactions in which the body’s immune system mistakenly attacks its own tissue.
Primary brain infections are most often caused by viral invasion. A large number of viruses can be potential culprits, some of which are carried by mosquitoes, ticks and other insects or animals. The most common causative agent is herpes simplex virus, HSV, which includes HSV-1 and HSV-2. HSV encephalitis tends to affect people younger than 20 years or older than 40, and is often fatal if not treated promptly.
Autoimmune encephalitis usually occurs as a secondary immunologic complication several weeks after certain infections or vaccinations. In this case, the immune system produces immune cells or antibodies against some brain proteins that resemble the proteins of the infectious agent.
Immunologically mediated encephalitis may also occur in patients with cancers or autoimmune disorders. Examples are anti-NMDA receptor encephalitis and VGKC-complex antibody encephalitis, in which the immune system targets NMDA receptor and VGKC protein complex, respectively.
Symptoms vary depending on the cause and the affected brain area, but often include fever, headache, stiff neck, sensitivity to light, altered mental status, cognitive problems and seizures.
Infectious encephalitis typically starts with flu-like symptoms and progresses over several days, while autoimmune encephalitis often evolves over the course of several weeks.
Some types of encephalitis are associated with specific symptoms such as sensation of déjà vu, certain unusual movement patterns, or hallucinations of disagreeable odors.
Encephalitis must be suspected in patients with sudden unexplained changes in mental status. Diagnosis is based on physical exam and medical history which may suggest different diagnostic tests for different patients. Most cases, however, require brain imaging studies, such as MRI, to detect edema and brain lesions; and cerebrospinal fluid analysis to identify the causative agent. MRI can also help rule out other conditions that produce similar symptoms.
Because prompt treatments are critical for survival, several medications may be started before the causative agent can be identified. Treatment with antiviral Acyclovir is often initiated immediately and continued until HSV and varicella-zoster virus encephalitides are excluded; empiric antibiotics may be given until bacterial cause is ruled out.
Treatment for autoimmune encephalitis may include corticosteroids, intravenous antibodies, and plasma exchange. Supportive therapy includes fever and inflammation reducer, intravenous fluids, and anti-seizure medications.