A84.9 ICD-10-CM Code: Tick-borne viral encephalitis, unspecified

A84.9 is the ICD-10-CM diagnosis code for tick-borne viral encephalitis, unspecified. This code describes inflammation of the brain caused by a virus transmitted through a tick bite, when the specific type of tick-borne encephalitis virus has not been identified. It represents a serious infection affecting brain function that requires medical attention. A84.9 sits in the ICD-10-CM chapter for certain infectious and parasitic diseases (a00-b99), within the section covering viral and prion infections of the central nervous system (a80-a89).

A84.9 is a billable ICD-10-CM code but does not map to a payment HCC under the CMS-HCC V28, V24, ESRD, or RxHCC risk adjustment models. It can be reported on Medicare Advantage encounter data submissions but it does not contribute to a beneficiary's RAF score and therefore does not affect risk-adjusted payments to the plan.

Use this code only when the specific tick-borne encephalitis virus (such as Powassan, Colorado tick fever, or Eastern equine encephalitis) cannot be determined from documentation; if the specific virus is identified, use the more specific A84.0-A84.8 codes instead.