A81.9 Atypical virus infection of central nervous system, unspecified

Billable ICD-10-CM code, FY2026. Acts as a Complication or Comorbidity (CC) as a secondary diagnosis.

Applicable to

• Prion diseases of the central nervous system NOS

Applies from A81 Atypical virus infections of central nervous system

Includes

• diseases of the central nervous system caused by prions

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-)

Risk adjustment (HCC)

• CMS-HCC V28: HCC 127 — Dementia, Mild or Unspecified
• RxHCC V08: HCC 112 — Dementia, Except Alzheimer's Disease
• ESRD V24: HCC 52

MS-DRG index

Defines the logic of DRG(s) 056-057 in MDC 01.

Approximate ICD-9-CM (GEMs)

• 046.9 Unspecified slow virus infection of central nervous system

Code annotations containing back-references to A81.9

Back-references to A81.9

• Code First: F02 Dementia in other diseases classified elsewhere ("prion disease (A81.9)")

Diagnosis Index entries for A81.9

• Disease, diseased › prion, central nervous system
• Infection, infected, infective (opportunistic) › atypical › virus
• Infection, infected, infective (opportunistic) › slow virus
• Infection, infected, infective (opportunistic) › virus, viral NOS › central nervous system › atypical
• Infection, infected, infective (opportunistic) › virus, viral NOS › central nervous system › slow virus
• Infection, infected, infective (opportunistic) › virus, viral NOS › slow

Nearby codes

• A81.8 Other atypical virus infections of central nervous system
• A81.81 Kuru
• A81.82 Gerstmann-Straussler-Scheinker syndrome
• A81.83 Fatal familial insomnia
• A81.89 Other atypical virus infections of central nervous system
• A81.9 Atypical virus infection of central nervous system, unspecified (this code)