ICD-10 Code A81 – Atypical Virus Infections of Central Nervous System (2026): Diagnosis, Symptoms & Billing Guide
2026 ICD-10-CM Diagnosis Code A81 – Atypical virus infections of central nervous system
What it is
A81 identifies atypical viral infections that affect the central nervous system. Use it when the record documents a viral CNS disease that is not classified elsewhere in ICD-10-CM.
Clinical signs
Clinical features vary; refer to documentation. Records may describe encephalitis, meningitis, or other CNS involvement caused by an atypical virus, with neurologic findings supporting the diagnosis.
When to use this code
Use A81 when the provider clearly documents an atypical viral infection of the brain, spinal cord, or meninges and no more specific ICD-10-CM code applies. Confirm that the diagnosis is established or specifically treated as the reason for care. If the note names a different viral CNS infection, code that condition instead.
Do not use for
Do not use this code for common viral CNS infections that have their own ICD-10-CM code. Do not assign it when the documentation is vague; check documentation.
Coding tip
Verify the exact viral diagnosis and CNS site in the provider note before coding A81.