1. ICD-10-CM Codes
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2. A00-B99
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3. A80-A89
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4. A83-
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5. 2023 ICD-10-CM Diagnosis Code A83.1

2023 ICD-10-CM Diagnosis Code A83.1

Western equine encephalitis

2016 2017 2018 2019 2020 2021 2022 2023 Billable/Specific Code

• A83.1 is a billable/specific ICD-10-CM code that can be used to indicate a diagnosis for reimbursement purposes.
• The 2023 edition of ICD-10-CM A83.1 became effective on October 1, 2022.
• This is the American ICD-10-CM version of A83.1 - other international versions of ICD-10 A83.1 may differ.

• A form of arboviral encephalitis (which primarily affects horses) endemic to western and central regions of north america. The causative organism (encephalomyelitis virus, western equine) may be transferred to humans via the bite of mosquitoes (culex tarsalis and others). Clinical manifestations include headache and influenza-like symptoms followed by alterations in mentation, seizures, and coma. Death occurs in a minority of cases. Survivors may recover fully or be left with residual neurologic dysfunction, including parkinsonism, postencephalitic. (from Joynt, Clinical Neurology, 1996, ch26, pp8-9)
• A mosquito-born viral infection caused by the western equine encephalitis virus. The signs and symptoms range from flu-like illness to permanent central nervous system damage, coma, and death.
• Form of arboviral encephalitis which primarily affects horses, endemic to western and central north america; the virus may be transferred to humans via mosquito bite; clinical manifestations include headache and influenza-like symptoms followed by alterations in mentation, seizures and coma; survivors may be left with residual neurologic dysfunction.

• 023 Craniotomy with major device implant or acute complex cns principal diagnosis with mcc or chemotherapy implant or epilepsy with neurostimulator
• 024 Craniotomy with major device implant or acute complex cns principal diagnosis without mcc
• 097 Non-bacterial infection of nervous system except viral meningitis with mcc
• 098 Non-bacterial infection of nervous system except viral meningitis with cc
• 099 Non-bacterial infection of nervous system except viral meningitis without cc/mcc

Convert A83.1 to ICD-9-CM

• 2016 (effective 10/1/2015): New code (first year of non-draft ICD-10-CM)
• 2017 (effective 10/1/2016): No change
• 2018 (effective 10/1/2017): No change
• 2019 (effective 10/1/2018): No change
• 2020 (effective 10/1/2019): No change
• 2021 (effective 10/1/2020): No change
• 2022 (effective 10/1/2021): No change
• 2023 (effective 10/1/2022): No change

• Encephalitis (chronic) (hemorrhagic) (idiopathic) (nonepidemic) (spurious) (subacute) G04.90
  ICD-10-CM Diagnosis Code G04.90

  Encephalitis and encephalomyelitis, unspecified

  2016 2017 2018 2019 2020 2021 2022 2023 Billable/Specific Code

  Applicable To

  • Ventriculitis (cerebral) NOS
  • equine (acute) (infectious) (viral) A83.9
    ICD-10-CM Diagnosis Code A83.9

    Mosquito-borne viral encephalitis, unspecified

    2016 2017 2018 2019 2020 2021 2022 2023 Billable/Specific Code
    • Western A83.1
  • viral, virus A86
    ICD-10-CM Diagnosis Code A86

    Unspecified viral encephalitis

    2016 2017 2018 2019 2020 2021 2022 2023 Billable/Specific Code

    Applicable To

    • Viral encephalomyelitis NOS
    • Viral meningoencephalitis NOS
    • arthropod-borne NEC A85.2
      ICD-10-CM Diagnosis Code A85.2

      Arthropod-borne viral encephalitis, unspecified

      2016 2017 2018 2019 2020 2021 2022 2023 Billable/Specific Code

      Type 1 Excludes

      • West nile virus with encephalitis (A92.31)
      • mosquito-borne A83.9
        ICD-10-CM Diagnosis Code A83.9

        Mosquito-borne viral encephalitis, unspecified

        2016 2017 2018 2019 2020 2021 2022 2023 Billable/Specific Code
        • Western equine A83.1
  • Western equine A83.1
• Encephalomyelitis G04.90
  - see also Encephalitis
  ICD-10-CM Diagnosis Code G04.90

  Encephalitis and encephalomyelitis, unspecified

  2016 2017 2018 2019 2020 2021 2022 2023 Billable/Specific Code

  Applicable To

  • Ventriculitis (cerebral) NOS
  • equine A83.9
    ICD-10-CM Diagnosis Code A83.9

    Mosquito-borne viral encephalitis, unspecified

    2016 2017 2018 2019 2020 2021 2022 2023 Billable/Specific Code
    • Western A83.1

Reimbursement claims with a date of service on or after October 1, 2015 require the use of ICD-10-CM codes.