To distinguish encephalitis from other causes of encephalopathy, core components of the presentation of encephalitis include the presence of fever (within 72 hours before or after presentation), cerebrospinal fluid (CSF) pleocytosis (≥ 5 /mm3), or MRI or electroencephalogram (EEG) changes consistent with encephalitis.
Encephalitis is often secondary to a virus but may be caused by bacteria, fungi, or toxins. Three of the most common etiologic agents for acute encephalitis are viral including herpes simplex virus (HSV), varicella-zoster virus (VZV), and enterovirus. Alternatively, encephalitis can be caused by autoimmune conditions (anti-NMDAR encephalitis, lupus cerebritis) or inflammatory or paraneoplastic conditions, or be a consequence of stem cell transplant. Patients with encephalitis may also have concomitant meningitis (meningoencephalitis).
Mimics of encephalitis include systemic infections without direct central nervous system (CNS) infection, metabolic derangements, toxic exposures, vascular disease, and some inflammatory states.
Related topics: Behçet syndrome, antibody-mediated encephalitis, viral encephalitides (see also California encephalitis group, Venezuelan equine encephalitis, Western equine encephalitis, Eastern equine encephalitis, St. Louis encephalitis, Japanese encephalitis, West Nile virus), varicella, herpes zoster
G04.90 – Encephalitis and encephalomyelitis, unspecified
45170000 – Encephalitis
Differential Diagnosis & Pitfalls
- Migraine headache
- Postictal state
- Central nervous system (CNS) lymphoma (see lymphomatous meningitis)
- Gliomatosis cerebri
- CNS vasculitis (see cerebral vasculitis)
- Post-traumatic (including postconcussive syndrome)
- Leigh syndrome
- MELAS syndrome (mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes)
- MERFF syndrome (myoclonic epilepsy with ragged-red fibers)
- Mitochondrial neurogastrointestinal encephalopathy