2027 ICD-10-CM Diagnosis Code A86Unspecified viral encephalitis
ICD-10-CM Codes›A00–B99›A80-A89›A86
- Billable — Valid for Submission
- CC — Complication or Comorbidity
- Not Chronic
A86 is a billable ICD-10-CM diagnosis code for unspecified viral encephalitis. It is valid on HIPAA claims for fiscal year 2027 (October 1, 2026 through September 30, 2027) and groups to MS-DRG 97 through 99, 974 through 976. As a secondary diagnosis, it counts as a complication or comorbidity (CC) and moves an inpatient stay to a higher severity level within its MS-DRG family. It does not count, however, when the principal diagnosis is one of 186 closely related codes. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Encephalitis and Viral infection.
Code Identity
Code Classification
Approximate SynonymsGuidance
Alternate terms and clinical phrases that map to this code.
- Acute encephalitis
- Acute necrotizing encephalitis
- Acute viral encephalitis
- Arenavirus encephalitis
- Arenavirus meningitis
- Chronic echovirus meningoencephalitis
- Chronic infectious disease of central nervous system
- Chronic meningitis
- Chronic viral encephalitis
- Dementia associated with viral encephalitis
- Echovirus encephalitis
- Epidemic encephalitis
- Infection caused by Lymphocytic choriomeningitis virus
- Infective ventriculitis
- Lymphocytic choriomeningitis virus encephalitis
- Meningitis caused by echovirus
- Meningitis caused by Enterovirus
- Meningitis caused by lymphocytic choriomeningitis virus
- Meningoencephalitis caused by Lymphocytic choriomeningitis virus
- Meningoencephalitis caused by virus
- Primary encephalitis
- Primary viral encephalitis
- Ventriculitis of the brain
- Viral encephalitis
- Viral ventriculitis
Instructional NotesGuidance
Instructions from the official ICD-10-CM Tabular List that apply to A86: its own notes plus those printed at block A80-A89 and Chapter 1. A note printed at a category, block or chapter applies to every code under it.
Includes
Further defines, or gives examples of, the content of the category.
- diseases generally recognized as communicable or transmissible
Applicable To
Conditions this code is used for: synonyms of the title or, for "other specified" codes, the conditions assigned to it. The list is not exhaustive.
- Viral encephalomyelitis NOS
- Viral meningoencephalitis NOS
Excludes1
Not coded here: the excluded code is never reported together with this one, unless the two conditions are unrelated.
Excludes2
Not included here: the excluded condition is not part of this code, but a patient may have both, so both codes may be reported.
- carrier or suspected carrier of infectious disease (Z22.-)
- certain localized infections - see body system-related chapters
- infectious and parasitic diseases complicating pregnancy, childbirth and the puerperium (O98.-)
- infectious and parasitic diseases specific to the perinatal period (P35-P39)
- influenza and other acute respiratory infections (J00-J22)
Use Additional Code
Add a second code, after this one, to fully describe the condition.
- code to identify resistance to antimicrobial drugs (Z16.-)
Source: CMS ICD-10-CM Tabular List. How to read instructional notes.
Referenced in Other NotesGuidance
Instructional notes printed at other codes that name A86, its category, or a range that includes it.
Index to Diseases and InjuriesGuidance
Alphabetical index entries that point to this code.
Encephalitis (chronic) (hemorrhagic) (idiopathic) (nonepidemic) (spurious) (subacute) G04.90
acute See Also: Encephalitis, viral; A86
Meningoencephalitis See Also: Encephalitis; G04.90
Meningoencephalomyelitis See Also: Meningoencephalitis;
Clinical ClassificationClinical
AHRQ’s CCSR groups this code into broader clinical categories.
Patient EducationClinical
Encephalitis
Encephalitis is inflammation (swelling) of the brain. It can happen when an infection or medical condition that affects the brain activates your immune system. The inflammation can cause a wide range of symptoms. In extreme cases, it can lead to brain damage, stroke, or even death.
The full article covers:
- What is encephalitis?
- What causes encephalitis?
- Who is more likely to get encephalitis?
- What are the symptoms of encephalitis?
- How is encephalitis diagnosed?
- What are the treatments for encephalitis?
- Can encephalitis be prevented?
Read the full article at MedlinePlus
Courtesy of MedlinePlus, a service of the U.S. National Library of Medicine.
Convert A86 to ICD-9-CMHistory
The closest ICD-9-CM equivalents under the General Equivalence Mappings.
Code HistoryHistory
Questions About A86Overview
What is the ICD-10 code for unspecified viral encephalitis?
The ICD-10-CM code for unspecified viral encephalitis is A86. It is billable on HIPAA-covered claims from October 1, 2026 through September 30, 2027.
Is A86 (Unspecified viral encephalitis) a billable code?
Yes. This is a billable ICD-10-CM code, specific enough to report unspecified viral encephalitis on HIPAA-covered claims from October 1, 2026 through September 30, 2027.
What MS-DRG does A86 group to?
When unspecified viral encephalitis is the principal diagnosis on an inpatient stay, it groups to MS-DRG 98, 974, 976, 99, 975, 97, with relative weights from 0.7879 to 3.8208 depending on complications. Higher weights mean higher Medicare reimbursement.
Is A86 a CC or MCC?
CMS lists A86 as a CC (complication or comorbidity) for FY 2027. Reported as a secondary diagnosis, it moves the inpatient stay to a higher-weighted DRG within its severity family. It does not count when the principal diagnosis is one of the 186 closely related codes in its exclusion list.
Can A86 be reported with G14?
Not as a rule. The Excludes1 note at block A80-A89, which applies to A86, lists "postpolio syndrome (G14)". An Excludes1 note means the excluded code is never reported together with this one; the only exception is when the two conditions are unrelated to each other (Official Guidelines, Section I.A.12.a).
