G04.91 Myelitis, 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)

Risk adjustment (HCC)

• CMS-HCC V28: HCC 182 — Spinal Cord Disorders/Injuries
• CMS-HCC V22: HCC 72 — Spinal Cord Disorders/Injuries
• RxHCC V08: HCC 155 — Spinal Cord Disorders
• ESRD V24: HCC 72

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 G04.91

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 G04.91

• Infection, infected, infective (opportunistic) › spinal cord NOS
• Myelitis (acute) (ascending) (childhood) (chronic) (descending) (diffuse) (disseminated) (idiopathic) (pressure) (progressive) (spinal cord) (subacute)
• Myeloradiculitis

Nearby codes

• 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
• G04.91 Myelitis, unspecified (this code)