Diagnostics

Management of encephalitis should focus on identifying and treating the underlying causes of encephalitis (see “Etiology” above).Diagnostic and treatment steps should be initiated simultaneously and empiric treatment should not be delayed for diagnostic steps.

• History and physical examination: detailed personal, travel, and exposure history

• All patients with suspected encephalitis require the following:

  • Neuroimaging (brain MRI with contrast)

  • Lumbar puncture

  • Electroencephalography

• Brain MRI with contrast: most sensitive and specific imaging modality

  • Indicated in all patients with suspected encephalitis

  • Limbic encephalitis: hyperintensity in the medial temporal lobes in T2/FLAIR sequence [5]

  • Herpes simplex encephalitis: hyperintense temporal lobe lesions and signal abnormalities in T2/FLAIR sequence (see “Neuroimaging” in “Herpes simplex encephalitis”)

  • Postinfectious encephalitis: multifocal white matter lesions in T2WI/FLAIR sequence [6]

• Brain CT (with or without contrast): indicated if MRI is not available or contraindicated

• Electroencephalography

  • Indicated in all patients with suspected encephalitis

  • Usually nonspecific findings

  • Used in cases of suspected viral encephalitis (see “Herpes simplex encephalitis EEG findings”) and inconclusive diagnosis of seizures (e.g., non-convulsive, subtle motor seizures)

A normal brain MRI does not exclude the diagnosis of encephalitis.

Always consider HSE when imaging suggests potential meningoencephalitis and temporal lobe involvement; bilateral temporal lobe abnormality is pathognomic of HSE.

• Blood studies

  • CBC, CRP, ESR, and blood cultures

  • Renal function tests and liver function tests

  • Coagulation panel

  • HIV testing

• CSF analysis

  • Perform PCR, Gram stain, and cultures

  • Viral and autoimmune encephalitis CSF findings

    • May be normal in immunocompromised patients

    • ↑ Lymphocytes (lymphocytic pleocytosis)

    • Inflammatory markers: ↑ IgG index and/or oligoclonal bands

Other studies

• Serologic studies: autoantibodies in CSF and serum (e.g., anti-Hu antibodies, anti-NMDAR antibodies)

• Brain biopsy: last resort

• Encephalopathies (e.g., toxins, electrolyte disturbances, uremia)

• Meningitis

• Epilepsy

• Vascular (e.g., stroke, thrombosis)

• Degenerative disorders (e.g., Alzheimer disease, frontotemporal dementia)