ICD-10-CM 2027
ICD-10 code for encephalomyelitis
Encephalitis and encephalomyelitis, unspecified
From the official ICD-10-CM alphabetic index entry “Encephalomyelitis”. Page updated September 29, 2026.
About coding encephalomyelitis
The ICD-10-CM code for encephalomyelitis is G04.90 (Encephalitis and encephalomyelitis, unspecified). The official index lists 24 more specific codes, so check the documentation for details such as type, cause, site or severity before settling on G04.90.
Within G04.9, choose G04.90 (Encephalitis and encephalomyelitis, unspecified) only when documentation doesn't support a more specific option: myelitis, unspecified (G04.91).
As a secondary diagnosis it is an MCC (major complication or comorbidity), which can move an inpatient stay into the highest-paying "with MCC" MS-DRG of its family, unless the principal diagnosis excludes it.
In MS-DRG v44.0, it is part of the grouping logic for DRG 023 (Craniotomy with Major Device Implant or Acute Complex CNS Principal Diagnosis with MCC or Antineoplastic Implant or Epilepsy with Neurostimulator, relative weight 5.7444), DRG 024 (Craniotomy with Major Device Implant or Acute Complex CNS Principal Diagnosis without MCC, relative weight 3.9708), DRG 097 (Non-Bacterial Infection of Nervous System Except Viral Meningitis with MCC, relative weight 3.8226), DRG 098 (Non-Bacterial Infection of Nervous System Except Viral Meningitis with CC, relative weight 2.2706), DRG 099 (Non-Bacterial Infection of Nervous System Except Viral Meningitis without CC/MCC, relative weight 1.5256), DRG 974 (HIV with Major Related Condition with MCC, relative weight 3.0506) and 2 more, in MDC 01 (Diseases and Disorders of the Nervous System) and MDC 25 (Human Immunodeficiency Virus Infections), as a principal or secondary diagnosis. The DRG a claim lands in depends on the principal diagnosis, procedures and any CC/MCC secondary diagnoses.
More specific encephalomyelitis codes (official index)
- acute disseminated G04.00 — Acute disseminated encephalitis and encephalomyelitis, unspecified
- infectious G04.01 — Postinfectious acute disseminated encephalitis and encephalomyelitis (postinfectious ADEM)
- noninfectious G04.81 — Other encephalitis and encephalomyelitis
- postimmunization G04.02 — Postimmunization acute disseminated encephalitis, myelitis and encephalomyelitis
- postinfectious G04.01 — Postinfectious acute disseminated encephalitis and encephalomyelitis (postinfectious ADEM)
- acute necrotizing hemorrhagic G04.30 — Acute necrotizing hemorrhagic encephalopathy, unspecified
- postimmunization G04.32 — Postimmunization acute necrotizing hemorrhagic encephalopathy
- postinfectious G04.31 — Postinfectious acute necrotizing hemorrhagic encephalopathy
- specified NEC G04.39 — Other acute necrotizing hemorrhagic encephalopathy
- equine A83.9 — Mosquito-borne viral encephalitis, unspecified
- Eastern A83.2 — Eastern equine encephalitis
- Venezuelan A92.2 — Venezuelan equine fever
- Western A83.1 — Western equine encephalitis
- in diseases classified elsewhere G05.3 — Encephalitis and encephalomyelitis in diseases classified elsewhere
- myalgic G93.32 — Myalgic encephalomyelitis/chronic fatigue syndrome
- chronic fatigue syndrome [ME/CFS] G93.32 — Myalgic encephalomyelitis/chronic fatigue syndrome
- postchickenpox B01.11 — Varicella encephalitis and encephalomyelitis
- postinfectious NEC G04.01 — Postinfectious acute disseminated encephalitis and encephalomyelitis (postinfectious ADEM)
- postmeasles B05.0 — Measles complicated by encephalitis
- postvaccinal G04.02 — Postimmunization acute disseminated encephalitis, myelitis and encephalomyelitis
- postvaricella B01.11 — Varicella encephalitis and encephalomyelitis
- rubella B06.01 — Rubella encephalitis
- specified NEC G04.81 — Other encephalitis and encephalomyelitis
- Venezuelan equine A92.2 — Venezuelan equine fever
Common questions about encephalomyelitis ICD-10 codes
What is the ICD-10 code for encephalomyelitis?
- G04.90 — Encephalitis and encephalomyelitis, unspecified. More specific codes apply when the documentation supports them: G04.00, G04.01, G04.81, G04.02 and others below.
What is the ICD-10 code for acute disseminated encephalomyelitis?
- G04.00 — Acute disseminated encephalitis and encephalomyelitis, unspecified.
What is the ICD-10 code for acute necrotizing hemorrhagic encephalomyelitis?
- G04.30 — Acute necrotizing hemorrhagic encephalopathy, unspecified.
What is the ICD-10 code for equine encephalomyelitis?
- A83.9 — Mosquito-borne viral encephalitis, unspecified.
What is the ICD-10 code for myalgic encephalomyelitis?
- G93.32 — Myalgic encephalomyelitis/chronic fatigue syndrome.
What is the ICD-10 code for postchickenpox encephalomyelitis?
- B01.11 — Varicella encephalitis and encephalomyelitis.
What is the ICD-10 code for postinfectious nec encephalomyelitis?
- G04.01 — Postinfectious acute disseminated encephalitis and encephalomyelitis (postinfectious ADEM).
Is G04.90 billable?
- Yes. G04.90 is a billable/specific ICD-10-CM code valid for FY2027 (October 1, 2026 – September 30, 2027).
Can G04.90 be used as a principal diagnosis?
- Yes. The Medicare Code Editor doesn't restrict G04.90 as a principal diagnosis.
Is G04.90 a CC or MCC?
- G04.90 is an MCC (major complication or comorbidity) under MS-DRG v44.0, unless excluded by the principal diagnosis.