G04.90 Encephalitis and encephalomyelitis, unspecified

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

Applicable to

• Ventriculitis (cerebral) NOS

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)

MS-DRG index

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

Approximate ICD-9-CM (GEMs)

• 323.9 Unspecified causes of encephalitis, myelitis, and encephalomyelitis (approximate)

Code annotations containing back-references to G04.90

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 G04.90

• Encephalitis (chronic) (hemorrhagic) (idiopathic) (nonepidemic) (spurious) (subacute)
• Encephalomyelitis
• Hematomyelitis
• Infection, infected, infective (opportunistic) › brain
• Meningoencephalitis
• Ventriculitis (cerebral)

Nearby codes

• G04.8 Other encephalitis, myelitis and encephalomyelitis
• G04.81 Other encephalitis and encephalomyelitis
• G04.82 Acute flaccid myelitis
• G04.89 Other myelitis
• G04.9 Encephalitis, myelitis and encephalomyelitis, unspecified
• G04.90 Encephalitis and encephalomyelitis, unspecified (this code)
• G04.91 Myelitis, unspecified