ICD-10 Code A86 – Unspecified viral encephalitis (2026): Diagnosis, Symptoms & Billing Guide
2026 ICD-10-CM Diagnosis Code A86 – Unspecified viral encephalitis
What it is
A86 identifies viral encephalitis when the specific virus is not documented. It refers to inflammation of the brain caused by a viral infection, with no more detailed organism named in the record.
Clinical signs
Clinical features vary; refer to documentation. Commonly, encephalitis presents with altered mental status, fever, headache, seizures, or focal neurologic findings, but the chart must support brain inflammation.
When to use this code
Use A86 when the provider documents viral encephalitis but does not identify the causative virus. It also fits when testing is pending or inconclusive and the final diagnosis remains unspecified viral encephalitis. Code the documented condition, not a suspected one.
Do not use for
Do not use A86 for encephalopathy without documented encephalitis, or for meningitis alone. If a specific viral cause is named, check documentation for a more precise code.
Coding tip
Look for explicit provider wording such as “viral encephalitis” and confirm that the organism is not specified before assigning A86.