2024 ICD-10-CM Diagnosis Code A83.1

Western equine encephalitis

• A83.1 is a billable/specific ICD-10-CM code that can be used to indicate a diagnosis for reimbursement purposes.
• The 2024 edition of ICD-10-CM A83.1 became effective on October 1, 2023.
• This is the American ICD-10-CM version of A83.1 – other international versions of ICD-10 A83.1 may differ.

The following code(s) above A83.1 contain annotation back-references

 that may be applicable to A83.1:

• A00-B99  Certain infectious and parasitic diseases
• A80-A89  Viral and prion infections of the central nervous system
• A83  Mosquito-borne viral encephalitis

Clinical Information

• 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.

ICD-10-CM A83.1 is grouped within Diagnostic Related Group(s) (MS-DRG v41.0):

• 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-CMCode History

• 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
• 2024 (effective 10/1/2023): No change

Diagnosis Index entries containing back-references to A83.1:

• Encephalitis (chronic) (hemorrhagic) (idiopathic) (nonepidemic) (spurious) (subacute) G04.90
  • equine (acute) (infectious) (viral) A83.9
    • Western A83.1
  • viral, virusA86
    • arthropod-borne NECA85.2
      • mosquito-borneA83.9
        • Western equine A83.1
  • Western equine A83.1
• EncephalomyelitisG04.90 – see also Encephalitis
  • equineA83.9
    • Western A83.1