ICD-10-CM 2027 diagnosis code

A81Atypical virus infections of central nervous system

Not billable — use a more specific code

A81 is a header code, so it can't be reported by itself. Choose one of the 5 more specific codes beneath it.

Code unchanged since ICD-10-CM took effect on October 1, 2015. Source: official FY2027 ICD-10-CM release from CDC/NCHS and CMS. Page updated September 29, 2026. About our data

About A81

A81 is the ICD-10-CM diagnosis code for atypical virus infections of central nervous system. It belongs to block A80-A89 (viral and prion infections of the central nervous system) and chapter 1 (certain infectious and parasitic diseases). It is a header code, so it can't be reported by itself; one of its 5 subcodes must be used instead.

To report this condition, pick the subcode that matches the documentation: A81.0 (disease), A81.1 (panencephalitis), A81.2 (leukoencephalopathy), A81.8 (system) and A81.9 (unspecified).

Use an additional 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) and 1 more.

It has been part of ICD-10-CM since the code set took effect on October 1, 2015 and hasn't changed since.

Specific codes under A81

Coding notes

IncludesFurther defines the content of the category

diseases of the central nervous system caused by prions

Use additional codeAdd a secondary code to fully describe the condition

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-)

Notes that apply from higher levels

Instructions written at a parent level also apply to A81.

Broader instructions also apply from A80-A89 Viral and prion infections of the central nervous system and Chapter 1: Certain infectious and parasitic diseases.

Code history

2016
2017
2018
2019
2020
2021
2022
2023
2024
2025
2026
2027

FY2016 (effective 10/1/2015): Added (first year of ICD-10-CM)
No changes since FY2016.

Common questions about A81

Is A81 billable?: No. A81 is a header code. Report one of its more specific subcodes instead.