2026 ICD-10-CM Diagnosis Code G04.81Other encephalitis and encephalomyelitis

ICD-10-CM Codes›G00–G99›G00-G09›G04

ICD-10-CM G04.81
CMSSource: CMS FY 2026 ICD-10-CM dataset · Effective Oct 1, 2025 – Sep 30, 2026

G04.81 is a billable ICD-10-CM diagnosis code for other encephalitis and encephalomyelitis. It is valid on HIPAA claims for fiscal year 2026 (October 1, 2025 through September 30, 2026) and groups to MS-DRG 974 through 976. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Encephalitis.

Code Identity

ICD-10-CM Code
G04.81
Billable Status
Yes — Valid for Submission
Code Describes
Other encephalitis and encephalomyelitis
Short Description
Other encephalitis and encephalomyelitis
Same as the full description in the CMS dataset.
Parent Code
G04.8
Other encephalitis, myelitis and encephalomyelitis

Code Classification

ChapterG00–G99Diseases of the nervous system
SectionG00-G09Inflammatory diseases of the central nervous system
CategoryG04Encephalitis, myelitis and encephalomyelitis
This CodeG04.81Other encephalitis and encephalomyelitis

Approximate SynonymsGuidance

Alternate terms and clinical phrases that map to this code.

  • Allergic encephalitis
  • Allergic encephalomyelitis
  • Autoimmune acquired autonomic encephalomyelitis
  • Autoimmune cerebellar inflammation
  • Autoimmune encephalitis
  • Autoimmune encephalitis caused by N-methyl D-aspartate receptor antibody
  • Autoimmune encephalitis caused by N-methyl-D-aspartate receptor antibody
  • Autoimmune limbic encephalitis
  • Autoimmune myelopathy
  • Autonomic disorder due to autoimmune encephalitis
  • Autonomic disorder due to encephalitis
  • Bickerstaff's brainstem encephalitis
  • Brainstem encephalitis
  • Chronic lymphocytic inflammation with pontine perivascular enhancement responsive to steroids
  • Dementia due to autoimmune encephalitis
  • Dementia due to Hashimoto encephalopathy
  • Encephalitis caused by human immunodeficiency virus type 2
  • Experimental allergic encephalomyelitis
  • Focal encephalitis
  • Granulomatous meningoencephalomyelitis
  • Human immunodeficiency virus encephalitis
  • Human immunodeficiency virus II infection
  • Infectious mononucleosis encephalitis
  • Limbic encephalitis
  • Limbic encephalitis with contactin-associated protein-like 2 antibodies
  • Limbic encephalitis with dipeptidyl-peptidase 6 antibodies
  • Limbic encephalitis with leucine-rich glioma-inactivated 1 antibodies
  • Limbic encephalitis with neurexin-3 antibodies
  • Limbic encephalitis with N-methyl-D-aspartate receptor antibodies
  • Meningoencephalomyelitis
  • Meningomyelitis
  • Non-herpetic acute limbic encephalitis
  • Post-transplant acute limbic encephalitis
  • Pyogranulomatous meningoencephalomyelitis
  • Rasmussen syndrome
  • Rasmussen syndrome, refractory
  • Retroviridae encephalitis

Tabular List NotesGuidance

Coding notes and annotation back-references applicable to this code.

Inclusion Terms

  • Noninfectious acute disseminated encephalomyelitis (noninfectious ADEM)

Index to Diseases and InjuriesGuidance

Alphabetical index entries that point to this code.

External Cause of Injuries IndexGuidance

References for this code in the External Cause of Injuries Index.

    • Encephalitis(chronic) (hemorrhagic) (idiopathic) (nonepidemic) (spurious) (subacute)
      • acute
        • disseminated
          • noninfectious
    • Encephalitis(chronic) (hemorrhagic) (idiopathic) (nonepidemic) (spurious) (subacute)
      • Rasmussen
    • Encephalitis(chronic) (hemorrhagic) (idiopathic) (nonepidemic) (spurious) (subacute)
      • specified NEC
    • Encephalitis(chronic) (hemorrhagic) (idiopathic) (nonepidemic) (spurious) (subacute)
      • suppurative
    • Encephalomyelitis
      • acute disseminated
        • noninfectious
    • Encephalomyelitis
      • specified NEC
    • Leukoencephalitis
    • Meningoencephalitis
      • specified organism NEC
    • Rasmussen encephalitis
    • Syndrome
      • Rasmussen

Clinical ClassificationClinical

AHRQ’s CCSR groups this code into broader clinical categories.

CCSR NVS002
Encephalitis
Default principal diagnosis: inpatient Yes · outpatient Yes

Clinical InformationClinical

  • Limbic Encephalitis

    a paraneoplastic syndrome marked by degeneration of neurons in the limbic system. clinical features include hallucinations, loss of episodic memory; anosmia; ageusia; temporal lobe epilepsy; dementia; and affective disturbance (depression). circulating anti-neuronal antibodies (e.g., anti-hu; anti-yo; anti-ri; and anti-ma2) and small cell lung carcinomas or testicular carcinoma are frequently associated with this syndrome.

  • Limbic Encephalitis

    a rare disorder characterized by degenerative changes in the limbic area of the brain. causes include infections and autoimmune conditions; it may also manifest as a paraneoplastic syndrome, most often caused by small cell lung carcinoma. signs and symptoms include behavioral changes, hallucinations and dementia.

  • Autoimmune Encephalitis

    inflammation of the brain secondary to an immune response triggered by the body itself.

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 G04.81 to ICD-9-CMHistory

The closest ICD-9-CM equivalents under the General Equivalence Mappings.

ICD-9-CM
323.81 Enceph & encephlalo NEC
Approximate The match is approximate rather than exact.

Code HistoryHistory

FY 2016AddedAdded to the ICD-10-CM code setEffective October 1, 2015, the first year of ICD-10-CM.
FY 2017–2025No changes
FY 2026CurrentCurrent code set, no changesEffective October 1, 2025 through September 30, 2026.

Questions About G04.81Overview

Is G04.81 (Other encephalitis, myelitis and encephalomyelitis) a billable code?

Yes. This is a billable ICD-10-CM code, specific enough to report other encephalitis and encephalomyelitis on HIPAA-covered claims from October 1, 2025 through September 30, 2026.

What MS-DRG does G04.81 group to?

When other encephalitis and encephalomyelitis is the principal diagnosis on an inpatient stay, it groups to MS-DRG 974, 975, 976, with relative weights from 0.8945 to 2.8860 depending on complications. Higher weights mean higher Medicare reimbursement.

What is the ICD-9 equivalent of G04.81?

Under the General Equivalence Mappings, other encephalitis and encephalomyelitis converts to ICD-9-CM 323.81 (enceph & encephlalo NEC). The mapping is approximate, so confirm the match fits the documentation.

Footnotes

[1] Not chronic - A diagnosis code that does not fit the criteria for chronic condition (duration, ongoing medical treatment, and limitations) is considered not chronic. Some codes designated as not chronic are acute conditions. Other diagnosis codes that indicate a possible chronic condition, but for which the duration of the illness is not specified in the code description (i.e., we do not know the condition has lasted 12 months or longer) also are considered not chronic.