What does ICD-10 code A81 mean?

ICD-10 code A81 is the standardized code used for atypical virus infections of central nervous system in medical records and coding systems.

When is ICD-10 code A81 used?

Doctors, hospitals, and insurers may use ICD-10 code A81 when recording atypical virus infections of central nervous system in a standardized format. This entry may also act as a broader category that points toward more specific child codes.

Does ICD-10 code A81 confirm a diagnosis?

No. A code helps standardize documentation and claims, but it should not be read as a substitute for a clinician's full assessment.

ICD10

ICD-10 Code A81: Atypical virus infections of central nervous system

Name: ICD-10 Code A81: Atypical virus infections of central nervous system
Creator: HealthAssure Clinical Team
Published: 2026-05-21T06:00:51.394Z

A81 is an ICD-10 diagnosis entry used to group records related to Atypical virus infections of central nervous system. You may see this entry in coding references, medical records, or claims workflows when a broader diagnosis category is being reviewed before a more specific code is chosen. ICD-10 entries help standardize how diagnoses are organized for coding, reporting, analytics, and documentation. This code sits within the broader ICD-10 area for Certain infectious and parasitic diseases (A00-B99).

Reviewed by HealthAssure Clinical TeamUpdated 21 May 2026

What is this code?

ICD-10 entries help standardize how diagnoses are organized for coding, reporting, analytics, and documentation. This code sits within the broader ICD-10 area for Certain infectious and parasitic diseases (A00-B99).

When is it used?

May be used when a clinician documents atypical virus infections of central nervous system in a patient's medical record.
May appear in hospital records, claims, referrals, and clinical documentation.
This code may act more like a grouping or parent code, so a more specific child code may be used in final documentation when available.

What it does not mean

A code alone does not explain severity, treatment plan, or outcome.
A medical code should not be treated as a substitute for a doctor's diagnosis or advice.
This entry may represent a broader category rather than the most specific billable code.

Code hierarchy

chapter

1Certain infectious and parasitic diseases (A00-B99)

block

A80-A89Viral and prion infections of the central nervous system

currentA80-A89

Official coding notes

Includes

diseases of the central nervous system caused by prions

Applicable to

code, if applicable, to identify:
dementia with anxiety (F02.84, F02.A4, F02.B4, F02.C4)
dementia with behavioral disturbance (F02.81-, F02.A1-, F02.B1-, F02.C1-)
dementia with mood disturbance (F02.83, F02.A3, F02.B3, F02.C3)
dementia with psychotic disturbance (F02.82, F02.A2, F02.B2, F02.C2)
dementia without behavioral disturbance (F02.80, F02.A0, F02.B0, F02.C0)
mild neurocognitive disorder due to known physiological condition (F06.7-)

Use additional code

code, if applicable, to identify:
dementia with anxiety (F02.84, F02.A4, F02.B4, F02.C4)
dementia with behavioral disturbance (F02.81-, F02.A1-, F02.B1-, F02.C1-)
dementia with mood disturbance (F02.83, F02.A3, F02.B3, F02.C3)
dementia with psychotic disturbance (F02.82, F02.A2, F02.B2, F02.C2)
dementia without behavioral disturbance (F02.80, F02.A0, F02.B0, F02.C0)
mild neurocognitive disorder due to known physiological condition (F06.7-)

Where you may see this code

You may see this entry in coding references, medical records, or claims workflows when a broader diagnosis category is being reviewed before a more specific code is chosen.

Related specialists

Infectious Disease SpecialistGeneral Physician

Sibling codes

A80Acute poliomyelitis A82Rabies A83Mosquito-borne viral encephalitis A84Tick-borne viral encephalitis A85Other viral encephalitis, not elsewhere classified A86Unspecified viral encephalitisbillable A87Viral meningitis A88Other viral infections of central nervous system, not elsewhere classified A89Unspecified viral infection of central nervous systembillable

Coding guidelines

Compatibility

Legacy code aligns to an official FY 2026 category. Frontend should resolve to the official category page and surface the billable child codes.

Legacy codes

A81

Replacement codes

A81.1 — Subacute sclerosing panencephalitisA81.2 — Progressive multifocal leukoencephalopathyA81.9 — Atypical virus infection of central nervous system, unspecified

Common synonyms

Atypical virus infections of central nervous system

Frequently asked questions

About this content

This page is prepared by HealthAssure's clinical team using official coding standards from ICD-10. AI tools assist with drafting explanations, which are then reviewed and verified by healthcare professionals for accuracy. This content is for informational purposes and does not replace professional medical advice. Meet our team.