ICD-10 Code A81.9 – Atypical virus infection of central nervous system, unspecified (2026): Diagnosis, Symptoms & Billing Guide
2026 ICD-10-CM Diagnosis Code A81.9 – Atypical virus infection of central nervous system, unspecified
What it is
This code identifies an unspecified atypical viral infection affecting the central nervous system. Use it when the record documents a viral CNS infection but does not name a specific virus or syndrome.
Clinical signs
Clinical features vary; refer to documentation. Typical CNS infection findings may include neurologic symptoms such as altered mental status, seizures, meningitis-like symptoms, or focal deficits, but the exact presentation depends on the virus.
When to use this code
Use A81.9 when the provider documents an atypical viral infection of the brain, spinal cord, or meninges without a more specific organism or diagnosis. It also fits when the chart confirms viral CNS disease but the exact type remains unspecified. Check documentation if another code describes the condition more precisely.
Do not use for
Do not use this code for a specified viral encephalitis, meningitis, or other named CNS infection when a more exact code is available. Avoid it when the record only suggests infection without confirmation.
Coding tip
Query for the specific virus or CNS syndrome before defaulting to A81.9.