Encephalitis

Overview

Encephalitis is a syndrome of brain inflammation that causes altered neurologic function. Infectious causes include herpes simplex virus, varicella-zoster virus, enteroviruses and mosquito- or tick-borne viruses, with geography and immune status influencing the list. Autoimmune encephalitis can follow infection, occur with tumors or arise without an obvious trigger. ^{[1] [2]}

Inflammation disrupts neuronal function and can cause swelling, seizures and abnormalities of consciousness, memory, behavior, language or movement. Some infectious agents directly invade neural tissue, while autoimmune disease targets neuronal surface proteins or other nervous-system structures. The same outward syndrome can therefore require very different definitive treatments. ^{[1] [2]}

A mild headache and fever alone do not establish encephalitis. The syndrome becomes more concerning when there is altered mental status, new seizures, focal neurologic findings, unusual behavior or reduced consciousness. Because herpes simplex encephalitis can progress rapidly and is treatable, clinicians often begin empiric intravenous acyclovir while diagnostic testing is underway when HSV is plausible. ^{[1] [2] [3]}

Symptoms and warning signs

Early symptoms can resemble influenza, with fever, headache, fatigue or body aches. More serious disease causes confusion, disorientation, personality or behavior change, marked sleepiness, seizures, weakness, speech or memory problems, movement abnormalities or coma. Infants can present with poor feeding, irritability, lethargy, vomiting or a bulging fontanel. ^{[1] [2]}

Any new seizure, major confusion, severe drowsiness, focal weakness, inability to speak normally, loss of consciousness or rapidly worsening severe headache with fever requires emergency medical care. Encephalitis can deteriorate quickly and may need airway support, seizure treatment and intensive neurologic monitoring. ^{[1] [2]}

Diagnosis

Evaluation combines neurologic examination with brain imaging and cerebrospinal-fluid analysis. Lumbar puncture measures cell counts, protein and glucose and provides material for PCR and other infectious tests. MRI is generally more sensitive than CT for inflammatory brain changes, while CT may be used rapidly to assess hemorrhage, mass effect or another emergency before lumbar puncture. ^{[1] [2]}

EEG can identify seizures, nonconvulsive status epilepticus or characteristic patterns. Blood and CSF testing is guided by geography, season, immune status, exposures and the clinical syndrome. Autoimmune-antibody panels may be appropriate when infectious testing is unrevealing or when psychiatric, movement, seizure and memory features suggest autoimmune encephalitis. ^{[1] [2] [3]}

Meningitis, stroke, brain tumor, toxic-metabolic encephalopathy, sepsis, substance intoxication or withdrawal, severe electrolyte disorders, primary psychiatric illness and nonconvulsive seizures can resemble encephalitis. Clinicians often investigate several possibilities simultaneously because delays in treating HSV, bacterial meningitis, seizures or stroke can be harmful. ^{[2] [3]}

Causes, risk factors and clinical context

Risk depends on cause. Infants, older adults and people with weakened immune systems are at increased risk for severe infectious disease. Mosquito and tick exposure matters for vector-borne viruses, while some autoimmune encephalitides have associations with tumors. Vaccination reduces risk from several viruses that can cause encephalitis. ^{[1] [2]}

The course ranges from a mild self-limited illness to fulminant brain swelling and coma. Some patients improve quickly once the correct treatment is started, while others need weeks of hospitalization and months of rehabilitation. Recovery of memory, behavior, speech and stamina can lag behind physical stabilization. ^{[1] [2] [3]}

Complications and why the diagnosis matters

Complications include status epilepticus, cerebral edema, aspiration, respiratory failure, autonomic instability, stroke-like deficits and lasting cognitive or psychiatric impairment. Children can have developmental consequences. Autoimmune encephalitis can relapse in some patients, and post-encephalitic epilepsy can persist after inflammation resolves. ^{[1] [2]}

Outcome varies strongly by cause, age, severity and treatment timing. HSV encephalitis has a much better prognosis with early antiviral treatment than without it, but neurologic deficits can remain. Autoimmune encephalitis can respond well to immunotherapy, though recovery may be gradual and relapses can occur. ^{[1] [2] [3]}

Treatment and management

Treatment begins with stabilization and empiric coverage for dangerous treatable causes. Intravenous acyclovir is commonly started when HSV encephalitis is possible. Antibiotics are added when bacterial meningitis has not been excluded. Confirmed autoimmune encephalitis can require corticosteroids, IV immunoglobulin, plasma exchange or other immunotherapy under neurology guidance. ^{[1] [2]}

Hospital care can include antiseizure medication, airway protection, oxygen or ventilation, fluid and electrolyte management, fever control and treatment of raised intracranial pressure. Nutrition, prevention of blood clots and pressure injuries, and management of agitation or autonomic instability are part of severe-case care. ^{[1] [2] [3]}

Do not delay emergency evaluation while trying to identify a specific virus at home. Steroids or other immunosuppression should not be started casually before infectious causes are assessed. Antiviral and antimicrobial dosing requires attention to kidney function, age and other patient factors. ^{[1] [2]}

Follow-up, recovery and prevention

Follow-up commonly addresses seizures, memory, mood, behavior, sleep, speech and mobility. Neuropsychology, speech-language therapy, occupational therapy and physical rehabilitation may be needed. Return to driving, work or school depends on seizure control and cognitive recovery rather than hospital discharge alone. ^{[1] [2]}

Vaccines prevent several infections that can cause encephalitis, including measles, mumps, rubella and varicella, and travel vaccines can prevent selected vector-borne diseases. Mosquito and tick bite prevention reduces risk where arboviruses circulate. Hand hygiene and avoiding sharing items during some viral illnesses can reduce transmission of precursor infections. ^{[1] [2] [3]}

Special situations and care pathway

Autoimmune encephalitis may present with prominent psychiatric symptoms, abnormal movements, memory loss or seizures, particularly in younger people. Immunocompromised patients have a broader pathogen differential and can have atypical CSF responses. Pregnancy affects imaging, antiviral and immunotherapy decisions and requires multidisciplinary care. ^{[1] [2] [3]}

Stabilize the patient, obtain urgent neuroimaging when indicated, perform lumbar puncture when safe, start empiric acyclovir and other antimicrobial therapy when appropriate, use EEG to detect seizures, and narrow treatment as infectious, autoimmune or other causes become clearer. Severe disease requires neurology and critical-care involvement. ^{[1] [2]}

When to seek urgent medical care

Call emergency services for new seizures, confusion, marked drowsiness, loss of consciousness, sudden focal weakness or speech problems, severe headache with fever and neurologic change, or rapid behavioral deterioration with impaired safety. ^{[1] [2]}

Sources

1. MedlinePlus / NIH — Encephalitis
2. NINDS — Encephalitis and Meningitis
3. MedlinePlus Medical Encyclopedia — Encephalitis

This article is based on trusted medical sources and is awaiting clinician review. It is not a substitute for personalized medical advice.