ICD-10-CM Code A86

Unspecified viral encephalitis

Version 2020 Billable Code

Valid for Submission

A86 is a billable code used to specify a medical diagnosis of unspecified viral encephalitis. The code is valid for the year 2020 for the submission of HIPAA-covered transactions. The ICD-10-CM code A86 might also be used to specify conditions or terms like acute necrotizing encephalitis, acute viral encephalitis, chronic echovirus meningoencephalitis, chronic meningitis, chronic viral encephalitis, dementia associated with viral encephalitis, etc

Short Description:Unspecified viral encephalitis
Long Description:Unspecified viral encephalitis

Tabular List of Diseases and Injuries

The Tabular List of Diseases and Injuries is a list of ICD-10 codes, organized "head to toe" into chapters and sections with guidance for inclusions, exclusions, descriptions and more. The following references are applicable to the code A86:

Inclusion Terms

Inclusion Terms
These terms are the conditions for which that code is to be used. The terms may be synonyms of the code title, or, in the case of "other specified" codes, the terms are a list of the various conditions assigned to that code. The inclusion terms are not necessarily exhaustive. Additional terms found only in the Alphabetic Index may also be assigned to a code.
  • Viral encephalomyelitis NOS
  • Viral meningoencephalitis NOS

Index to Diseases and Injuries

The Index to Diseases and Injuries is an alphabetical listing of medical terms, with each term mapped to one or more ICD-10 code(s). The following references for the code A86 are found in the index:


The following clinical terms are approximate synonyms or lay terms that might be used to identify the correct diagnosis code:

  • Acute necrotizing encephalitis
  • Acute viral encephalitis
  • Chronic echovirus meningoencephalitis
  • Chronic meningitis
  • Chronic viral encephalitis
  • Dementia associated with viral encephalitis
  • Echovirus disease
  • Echovirus meningitis
  • Enterovirus meningitis
  • Epidemic encephalitis
  • Infective ventriculitis
  • Primary encephalitis
  • Primary viral encephalitis
  • Ventriculitis of the brain
  • Viral encephalitis
  • Viral meningoencephalitis
  • Viral ventriculitis

Clinical Information

  • ENCEPHALITIS CALIFORNIA-. a viral infection of the brain caused by serotypes of california encephalitis virus encephalitis virus california transmitted to humans by the mosquito aedes triseriatus. the majority of cases are caused by the la crosse virus. this condition is endemic to the midwestern united states and primarily affects children between 5 10 years of age. clinical manifestations include fever; vomiting; headache; and abdominal pain followed by seizures altered mentation and focal neurologic deficits. from joynt clinical neurology 1996 ch26 p13
  • ENCEPHALITIS ARBOVIRUS-. infections of the brain caused by arthropod borne viruses i.e. arboviruses primarily from the families togaviridae; flaviviridae; bunyaviridae; reoviridae; and rhabdoviridae. life cycles of these viruses are characterized by zoonoses with birds and lower mammals serving as intermediate hosts. the virus is transmitted to humans by the bite of mosquitoes culicidae or ticks. clinical manifestations include fever headache alterations of mentation focal neurologic deficits and coma. from clin microbiol rev 1994 jan;71:89 116; walton brain's diseases of the nervous system 10th ed p321
  • ENCEPHALITIS JAPANESE-. a mosquito borne encephalitis caused by the japanese b encephalitis virus encephalitis virus japanese occurring throughout eastern asia and australia. the majority of infections occur in children and are subclinical or have features limited to transient fever and gastrointestinal symptoms. inflammation of the brain spinal cord and meninges may occur and lead to transient or permanent neurologic deficits including a poliomyelitis like presentation; seizures; coma; and death. from adams et al. principles of neurology 6th ed p751; lancet 1998 apr 11;3519109:1094 7
  • ENCEPHALITIS VIRAL-. inflammation of brain parenchymal tissue as a result of viral infection. encephalitis may occur as primary or secondary manifestation of togaviridae infections; herpesviridae infections; adenoviridae infections; flaviviridae infections; bunyaviridae infections; picornaviridae infections; paramyxoviridae infections; orthomyxoviridae infections; retroviridae infections; and arenaviridae infections.

Convert A86 to ICD-9

  • 049.9 - Viral encephalitis NOS (Approximate Flag)

Code Classification

  • Certain infectious and parasitic diseases (A00–B99)
    • Viral and prion infections of the central nervous system (A80-A89)
      • Unspecified viral encephalitis (A86)

Code History

  • FY 2016 - New Code, effective from 10/1/2015 through 9/30/2016
    (First year ICD-10-CM implemented into the HIPAA code set)
  • FY 2017 - No Change, effective from 10/1/2016 through 9/30/2017
  • FY 2018 - No Change, effective from 10/1/2017 through 9/30/2018
  • FY 2019 - No Change, effective from 10/1/2018 through 9/30/2019
  • FY 2020 - No Change, effective from 10/1/2019 through 9/30/2020

Information for Patients


Encephalitis is an inflammation of the brain. Usually the cause is a viral infection, but bacteria can also cause it. It can be mild or severe. Most cases are mild. You may have flu-like symptoms. With a mild case, you may just need rest, plenty of fluids, and a pain reliever.

Severe cases need immediate treatment. Symptoms of severe cases include

  • Severe headache
  • Sudden fever
  • Drowsiness
  • Vomiting
  • Confusion
  • Seizures

In babies, additional symptoms may include constant crying, poor feeding, body stiffness, and bulging in the soft spots of the skull.

Severe cases may require a stay in the hospital. Treatments include oral and intravenous (IV) medicines to reduce inflammation and treat infection. Patients with breathing difficulties may need artificial respiration. Some people may need physical, speech, and occupational therapy once the illness is under control.

NIH: National Institute of Neurological Disorders and Stroke

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Viral Infections

Viruses are very tiny germs. They are made of genetic material inside of a protein coating. Viruses cause familiar infectious diseases such as the common cold, flu and warts. They also cause severe illnesses such as HIV/AIDS, smallpox, and Ebola.

Viruses are like hijackers. They invade living, normal cells and use those cells to multiply and produce other viruses like themselves. This can kill, damage, or change the cells and make you sick. Different viruses attack certain cells in your body such as your liver, respiratory system, or blood.

When you get a virus, you may not always get sick from it. Your immune system may be able to fight it off.

For most viral infections, treatments can only help with symptoms while you wait for your immune system to fight off the virus. Antibiotics do not work for viral infections. There are antiviral medicines to treat some viral infections. Vaccines can help prevent you from getting many viral diseases.

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