ICD-10 Code A84.0 – Far Eastern tick-borne encephalitis [Russian spring-summer encephalitis] (2026): Diagnosis, Symptoms & Billing Guide
2026 ICD-10-CM Diagnosis Code A84.0 – Far Eastern tick-borne encephalitis [Russian spring-summer encephalitis]
What it is
A84.0 identifies Far Eastern tick-borne encephalitis, a viral infection of the central nervous system spread by tick exposure. Use it when the record specifically documents this subtype of tick-borne encephalitis.
Clinical signs
Clinical features vary; refer to documentation. Typical encephalitis findings may include fever, headache, altered mental status, meningismus, or neurologic deficits, but you should code only when the diagnosis is confirmed or clearly documented.
When to use this code
Use A84.0 when the clinician documents Far Eastern tick-borne encephalitis or Russian spring-summer encephalitis. It is also appropriate when the chart clearly links encephalitis to this specific tick-borne viral illness. Check documentation if the subtype is not named.
Do not use for
Do not use this code for nonspecific viral encephalitis, other tick-borne infections, or suspected exposure without a documented diagnosis. If the record names a different encephalitis subtype, code that condition instead.
Coding tip
Match the exact encephalitis subtype in the provider note before assigning A84.0.