What are the symptoms of encephalitis?

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From the Guidelines

The symptoms of encephalitis include fever, headache, confusion, altered mental status, seizures, and neck stiffness, and can be life-threatening if not promptly diagnosed and treated. Patients may also experience drowsiness, nausea, vomiting, sensitivity to light, and in severe cases, coma 1. The onset can be sudden or gradual, with neurological symptoms typically developing after initial flu-like symptoms. Speech or behavioral changes, hallucinations, and movement disorders may also occur. The severity varies widely, with some people experiencing mild symptoms while others develop life-threatening complications. These symptoms result from inflammation of the brain tissue, typically caused by viral infections (like herpes simplex virus, arboviruses, or enteroviruses), though bacterial, fungal, or autoimmune causes are also possible 1. The inflammation disrupts normal brain function, leading to the neurological manifestations.

Key Symptoms

  • Fever
  • Headache
  • Confusion
  • Altered mental status
  • Seizures
  • Neck stiffness
  • Drowsiness
  • Nausea
  • Vomiting
  • Sensitivity to light
  • Coma (in severe cases)

Importance of Prompt Diagnosis and Treatment

If you suspect encephalitis, seek immediate medical attention as prompt diagnosis and treatment significantly improve outcomes and reduce the risk of long-term complications 1. It is essential to distinguish between infectious encephalitis and postinfectious or postimmunization encephalitis or encephalomyelitis, as the management approach is different 1. Encephalitis should also be distinguished from encephalopathy, which is defined by a disruption of brain function in the absence of a direct inflammatory process in the brain parenchyma 1.

From the Research

Symptoms of Encephalitis

The symptoms of encephalitis can vary depending on the brain zone affected, but common symptoms include:

  • Fever 2, 3, 4
  • Headache 3, 4
  • Confusion 2, 3, 5
  • Stiff neck 3
  • Seizures 2, 3, 4, 5
  • Weakness 3
  • Hallucinations 3
  • Coma 3
  • Focal neurological deficits 2, 4, 5
  • Movement disorder 2
  • Altered level of consciousness 2, 4

Severity of Symptoms

The symptoms of encephalitis can range from mild to severe, and can affect individuals of all ages, but it is frequently observed in pediatric and elderly populations 3. In some cases, encephalitis can cause long-term neuropsychiatric disorders, neurocognitive impairment, and degenerative diseases 3.

Diagnostic Findings

Diagnostic findings for encephalitis may include:

  • Pleocytosis in cerebrospinal fluid (CSF) analysis 5
  • Elevated protein levels in CSF analysis 5
  • Normal glucose concentrations in CSF analysis 5
  • Abnormal magnetic resonance imaging (MRI) scans 5
  • Epileptiform discharges on electroencephalogram (EEG) 5

References

Guideline

Guideline Directed Topic Overview

Dr.Oracle Medical Advisory Board & Editors, 2025

Research

Acute encephalitis - diagnosis and management.

Clinical medicine (London, England), 2018

Research

The Causes and Long-Term Consequences of Viral Encephalitis.

Frontiers in cellular neuroscience, 2021

Research

Encephalitis.

Neurologic clinics, 1999

Professional Medical Disclaimer

This information is intended for healthcare professionals. Any medical decision-making should rely on clinical judgment and independently verified information. The content provided herein does not replace professional discretion and should be considered supplementary to established clinical guidelines. Healthcare providers should verify all information against primary literature and current practice standards before application in patient care. Dr.Oracle assumes no liability for clinical decisions based on this content.

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