ICD-10 Code A84 – Tick-borne viral encephalitis (2026): Diagnosis, Symptoms & Billing Guide
2026 ICD-10-CM Diagnosis Code A84 – Tick-borne viral encephalitis
What it is
A84 identifies tick-borne viral encephalitis, a viral infection of the brain transmitted by tick bite. It is used when documentation states this specific tick-borne encephalitis diagnosis.
Clinical signs
Clinical features vary; refer to documentation. Commonly reported findings include fever, headache, meningitis or encephalitis symptoms, and neurologic changes such as confusion, weakness, or altered consciousness.
When to use this code
Use A84 when the provider documents tick-borne viral encephalitis, tick-borne encephalitis, or an equivalent confirmed diagnosis. Code it for encounters focused on the active neurologic infection or its evaluation. If the record only notes tick exposure or suspected encephalitis, check documentation before assigning this code.
Do not use for
Do not use A84 for nonspecific viral meningitis, other encephalitis causes, or tick-borne illnesses without encephalitis. If the diagnosis is uncertain or differs in the chart, check documentation.
Coding tip
Confirm the provider links the encephalitis to a tick-borne viral cause before assigning A84.