G04.02 Postimmunization acute disseminated encephalitis, myelitis and encephalomyelitis

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

Applicable to

• Encephalitis, post immunization
• Encephalomyelitis, post immunization

Use additional code

• code to identify the vaccine (T50.A-, T50.B-, T50.Z-)

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)

• 323.51 Encephalitis and encephalomyelitis following immunization procedures (approximate)
• 323.52 Myelitis following immunization procedures (approximate)

Code annotations containing back-references to G04.02

Back-references to G04.02

• Type 2 Excludes: T88.1 Other complications following immunization, not elsewhere classified ("postimmunization encephalitis (G04.02)")

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 G04.02

• Complication (s) (from) (of) › vaccination › encephalitis or encephalomyelitis
• Complication (s) (from) (of) › vaccination › myelitis
• Encephalitis (chronic) (hemorrhagic) (idiopathic) (nonepidemic) (spurious) (subacute) › acute › disseminated › postimmunization (postvaccination)
• Encephalitis (chronic) (hemorrhagic) (idiopathic) (nonepidemic) (spurious) (subacute) › due to › smallpox inoculation
• Encephalitis (chronic) (hemorrhagic) (idiopathic) (nonepidemic) (spurious) (subacute) › following vaccination or other immunization procedure
• Encephalitis (chronic) (hemorrhagic) (idiopathic) (nonepidemic) (spurious) (subacute) › postimmunization
• Encephalitis (chronic) (hemorrhagic) (idiopathic) (nonepidemic) (spurious) (subacute) › postvaccinal
• Encephalomyelitis › acute disseminated › postimmunization
• Encephalomyelitis › postvaccinal
• Encephalopathy (acute) › in (due to) (with) › vaccination
• Leukoencephalitis › acute (subacute) hemorrhagic › postimmunization or postvaccinal
• Leukoencephalopathy › postimmunization and postvaccinal
• Meningoencephalomyelitis › acute NEC (viral) › disseminated › postimmunization or postvaccination
• Meningoencephalomyelitis › postimmunization or postvaccination
• Myelitis (acute) (ascending) (childhood) (chronic) (descending) (diffuse) (disseminated) (idiopathic) (pressure) (progressive) (spinal cord) (subacute) › postimmunization
• Myelitis (acute) (ascending) (childhood) (chronic) (descending) (diffuse) (disseminated) (idiopathic) (pressure) (progressive) (spinal cord) (subacute) › postvaccinal

Nearby codes

• G04 Encephalitis, myelitis and encephalomyelitis
• G04.0 Acute disseminated encephalitis and encephalomyelitis (ADEM)
• G04.00 Acute disseminated encephalitis and encephalomyelitis, unspecified
• G04.01 Postinfectious acute disseminated encephalitis and encephalomyelitis (postinfectious ADEM)
• G04.02 Postimmunization acute disseminated encephalitis, myelitis and encephalomyelitis (this code)
• G04.1 Tropical spastic paraplegia
• G04.2 Bacterial meningoencephalitis and meningomyelitis, not elsewhere classified
• G04.3 Acute necrotizing hemorrhagic encephalopathy
• G04.30 Acute necrotizing hemorrhagic encephalopathy, unspecified
• G04.31 Postinfectious acute necrotizing hemorrhagic encephalopathy