G04.00 Acute disseminated encephalitis and encephalomyelitis, unspecified

Billable ICD-10-CM code, FY2026. Acts as a Major Complication or Comorbidity (MCC) as a secondary diagnosis.

Applies from G04 Encephalitis, myelitis and encephalomyelitis

Includes

• acute ascending myelitis
• meningoencephalitis
• meningomyelitis

Excludes1 (never code together)

• encephalopathy NOS (G93.40)

Excludes2 (not included here)

• acute transverse myelitis (G37.3)
• alcoholic encephalopathy (G31.2)
• multiple sclerosis (G35-)
• myalgic encephalomyelitis (G93.32)
• subacute necrotizing myelitis (G37.4)
• toxic encephalitis (G92.8)
• toxic encephalopathy (G92.8)

Applies from G04.0 Acute disseminated encephalitis and encephalomyelitis (ADEM)

Excludes1 (never code together)

• acute necrotizing hemorrhagic encephalopathy (G04.3-)
• other noninfectious acute disseminated encephalomyelitis (noninfectious ADEM) (G04.81)

MS-DRG index

Defines the logic of DRG(s) 023-024 in MDC 01.

Approximate ICD-9-CM (GEMs)

• 323.61 Infectious acute disseminated encephalomyelitis (ADEM) (approximate)

Code annotations containing back-references to G04.00

Back-references to G04.0

• Type 1 Excludes: G04.3 Acute necrotizing hemorrhagic encephalopathy ("acute disseminated encephalitis and encephalomyelitis (G04.0-)")

Back-references to G04

• Type 1 Excludes: G03 Meningitis due to other and unspecified causes ("meningoencephalitis (G04.-)")
• Type 1 Excludes: G03 Meningitis due to other and unspecified causes ("meningomyelitis (G04.-)")
• Type 2 Excludes: G95 Other and unspecified diseases of spinal cord ("myelitis (G04.-)")

Diagnosis Index entries for G04.00

• Encephalitis (chronic) (hemorrhagic) (idiopathic) (nonepidemic) (spurious) (subacute) › acute › disseminated
• Encephalitis (chronic) (hemorrhagic) (idiopathic) (nonepidemic) (spurious) (subacute) › disseminated, acute
• Encephalomyelitis › acute disseminated
• Meningoencephalomyelitis › acute NEC (viral) › disseminated

Nearby codes

• G04 Encephalitis, myelitis and encephalomyelitis
• G04.0 Acute disseminated encephalitis and encephalomyelitis (ADEM)
• G04.00 Acute disseminated encephalitis and encephalomyelitis, unspecified (this code)
• G04.01 Postinfectious acute disseminated encephalitis and encephalomyelitis (postinfectious ADEM)
• G04.02 Postimmunization acute disseminated encephalitis, myelitis and encephalomyelitis
• G04.1 Tropical spastic paraplegia
• G04.2 Bacterial meningoencephalitis and meningomyelitis, not elsewhere classified
• G04.3 Acute necrotizing hemorrhagic encephalopathy