What is ICD-10 code G05.4?

G05.4 is the ICD-10-CM diagnosis code for Myelitis in diseases classified elsewhere. Inflammation of the spinal cord that develops as a result of another disease the patient has. It belongs to the ICD-10-CM chapter for diseases of the nervous system (g00-g99). G05.4 is a billable code, meaning it can be reported on a claim as a primary or secondary diagnosis when supported by documentation. G05.4 is part of the FY2026 ICD-10-CM code set published by the CMS National Center for Health Statistics and used on Medicare, Medicaid, and commercial claims in the United States.

Yes. G05.4 is a billable ICD-10-CM code that can be reported on professional and institutional claims as a primary or secondary diagnosis when the provider documentation supports the specific condition described. Billable codes in ICD-10-CM are coded to the highest level of specificity available for the documented diagnosis. G05.4 is current for fiscal year 2026 and remains in the active CMS ICD-10-CM code set published by the National Center for Health Statistics.

What is the V28 vs V24 difference for G05.4?

CMS phased in the V28 risk adjustment model over payment years 2024 (33%), 2025 (67%), and 2026 (100%), replacing V24. V28 consolidates HCC categories, removes some lower-acuity conditions, and recalibrates RAF weights across the entire model. For G05.4, V28 maps to Spinal Cord Disorders/Injuries at RAF 0.282 while V24 mapped to Spinal Cord Disorders/Injuries at RAF 0.464. Both models can still appear in legacy data and in payer-specific lookback periods.

What should coders know when reporting G05.4?

Always pair this code with the underlying disease code (e.g., tuberculosis, syphilis, fungal infection) Review the Excludes1 notes to ensure the underlying condition isn't already included in another code Because G05.4 maps to a payment HCC, the documentation must also satisfy MEAT criteria (Monitor, Evaluate, Assess, or Treat) for the encounter to count toward the patient's risk adjustment score.

G05.4 ICD-10 Code: Myelitis in diseases classified

ICD-10-CM Code View

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Digital ICD-10 code-book layout with official code detail, always-visible risk models, Code Trumping, and Buddy coding guidance.

Code lookupG05.4Effective periodFY2026 Apr Update (Apr 1-Sep 30)

FY 2026 Apr update / Diseases of the nervous system (G00-G99) / Inflammatory diseases of the central nervous system (G00-G09)

G05.4

Billable / SpecificICD-10-CMOfficial ICD-10-CMCodebook guidance

Myelitis in diseases classified elsewhere

Inflammation of the spinal cord that develops as a result of another disease the patient has.

Buddy Insight

Myelitis in diseases classified elsewhere is a manifestation code indicating that spinal cord inflammation has developed secondary to another systemic disease.

CMS-HCC V28

Mapped

HCC 182

Spinal Cord Disorders/Injuries

RAF 0.282

CMS-HCC V24

Mapped

HCC 72

Spinal Cord Disorders/Injuries

RAF 0.464

ACA/HHS

Not risk-adjusted for this model/period.

RAF 0

ESRD/PACE

Mapped

HCC 72

Spinal Cord Disorders/Injuries

RAF 0.0

RXHCC

Mapped

HCC 155

Myelitis and Encephalomyelitis

RAF 0.0

Code Trumping

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Code Book Path

Official

G05Encephalitis, myelitis and encephalomyelitis in diseases classified elsewhere

G05.4Myelitis in diseases classified elsewhere

Inclusion Terms

Official

Meningomyelitis in diseases classified elsewhere

Excludes 2

Official

ICD-10-CM does not list Excludes 2 notes for G05.4 in this effective period.

Related Child Codes

Official

G05.3Encephalitis and encephalomyelitis in diseases classified elsewhere

Includes

Official

ICD-10-CM does not list Includes notes for G05.4 in this effective period.

Excludes 1

Official

adenoviral encephalitis, myelitis and encephalomyelitis (A85.1)
encephalitis, myelitis and encephalomyelitis (in) measles (B05.0)
enteroviral encephalitis, myelitis and encephalomyelitis (A85.0)
herpesviral [herpes simplex] encephalitis, myelitis and encephalomyelitis (B00.4)
listerial encephalitis, myelitis and encephalomyelitis (A32.12)

Code First

Official

underlying disease, such as:
congenital toxoplasmosis encephalitis, myelitis and encephalomyelitis (P37.1)
cytomegaloviral encephalitis, myelitis and encephalomyelitis (B25.8)
encephalitis, myelitis and encephalomyelitis (in) systemic lupus erythematosus (M32.19)
eosinophilic meningoencephalitis (B83.2)

Use Additional

Official

ICD-10-CM does not list Use Additional Code instructions for G05.4 in this effective period.

Code Also

Official

ICD-10-CM does not list Code Also instructions for G05.4 in this effective period.

Buddy Documentation Tip

HCC Buddy guidance

Documented underlying disease causing the myelitis (tuberculosis, syphilis, lupus, etc.)

Clinical evidence of spinal cord inflammation as a complication of the underlying disease

Clear causal link between the underlying condition and myelitis documented by provider

Neurological examination findings specific to myelitis

MEAT Support

HCC Buddy guidance

Documented underlying disease causing the myelitis (tuberculosis, syphilis, lupus, etc.)

Clinical evidence of spinal cord inflammation as a complication of the underlying disease

Clear causal link between the underlying condition and myelitis documented by provider

Neurological examination findings specific to myelitis

Audit Caution

HCC Buddy guidance

Failing to code the underlying disease first — G05.4 is a manifestation code and cannot be sequenced as primary

Using G05.4 without identifying and coding the underlying disease that caused the myelitis

Not reviewing Excludes1 notes to ensure the underlying condition code does not already include the myelitis

Confusing this manifestation code with primary myelitis codes in the G04 category

Common Mistakes

HCC Buddy guidance

G04.89 — Other myelitis: use when myelitis is a primary diagnosis, not secondary to another classified disease

G04.91 — Myelitis, unspecified: use when cause is unknown; G05.4 requires a known underlying disease

G04.1 — Tropical spastic paraplegia: specific HTLV-1 associated myelitis has its own code

G37.3 — Acute transverse myelitis in demyelinating disease: specific to demyelinating disease context

Last updated: FY2026 ICD-10-CM Apr update, Apr 1, 2026 through Sep 30, 2026. CMS-HCC V28 is 100% phased in for payment year 2026.

Is G05.4 an HCC code?

Yes. G05.4 maps to Spinal Cord Disorders/Injuries under the CMS-HCC V28 risk adjustment model (and Spinal Cord Disorders/Injuries under V24).

HCC Category Mapping

V28HCC 182, Spinal Cord Disorders/Injuries

0.282

V24HCC 72, Spinal Cord Disorders/Injuries

0.464

ESRDHCC 72, Spinal Cord Disorders/Injuries

0.000

RxHCCHCC 155, Myelitis and Encephalomyelitis

0.000

RAF weights shown are the community, non-dual, aged base weights from the CMS risk adjustment model file. Actual per-patient RAF contribution depends on member segment, interactions, and the model year used by the payer. V28 is the CMS-HCC model phased in over payment years 2024–2026; V24 remains in use during the transition and for historical data.

MEAT Criteria for G05.4

For G05.4to count as a valid HCC diagnosis in a given encounter, the provider's documentation must show MEAT: Monitor, Evaluate, Assess, or Treat. A diagnosis from a prior year does not carry forward automatically, it has to be re-documented and supported each calendar year.

MMonitor: signs, symptoms, disease progression, or lab trending documented in the note
EEvaluate: test results, medication response, or physical findings reviewed by the provider
AAssess: explicit mention in the assessment or plan with acknowledgment of status
TTreat: medication, referral, procedure, therapy, or counseling tied to the diagnosis

Only one of M/E/A/T is required to support the code, but the documentation must be specific enough to show that the provider actually addressed G05.4 during that encounter, not just copy-forwarded from a problem list.

What This Code Means

G05.4 is the ICD-10-CM diagnosis code for myelitis in diseases classified elsewhere. Inflammation of the spinal cord that develops as a result of another disease the patient has. G05.4 sits in the ICD-10-CM chapter for diseases of the nervous system (g00-g99), within the section covering inflammatory diseases of the central nervous system (g00-g09).

Under the CMS-HCC V28 risk adjustment model, G05.4 maps to Spinal Cord Disorders/Injuries (HCC 182) with a community, non-dual, aged base RAF weight of 0.282. Under the older V24 model, G05.4 mapped to the same category but with a base RAF weight of 0.464, V28 recalibrated weights across the entire model. V28 is the CMS-HCC risk adjustment model that reached 100% phase-in for payment year 2026, replacing V24 which was used during the PY2024–PY2025 transition.

Always pair this code with the underlying disease code (e.g., tuberculosis, syphilis, fungal infection). Because G05.4 maps to a payment HCC, the provider's documentation must satisfy MEAT criteria (Monitor, Evaluate, Assess, or Treat) for the encounter to count toward the patient's Medicare Advantage risk adjustment score. When documentation is ambiguous, coders should issue a provider query rather than assume the highest-specificity variant.

HCC Buddy maintains structured V28 and V24 mapping, RAF weights, and MEAT documentation criteria for G05.4 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.

Coding Tips

•Always pair this code with the underlying disease code (e.g., tuberculosis, syphilis, fungal infection)
•Review the Excludes1 notes to ensure the underlying condition isn't already included in another code

Clinical Significance

Myelitis in diseases classified elsewhere is a manifestation code indicating that spinal cord inflammation has developed secondary to another systemic disease. This dual-coding requirement reflects the complexity of the patient's condition and the increased resource utilization from managing both the underlying disease and its neurological complication.

Documentation Requirements

✓Documented underlying disease causing the myelitis (tuberculosis, syphilis, lupus, etc.)
✓Clinical evidence of spinal cord inflammation as a complication of the underlying disease
✓Clear causal link between the underlying condition and myelitis documented by provider
✓Neurological examination findings specific to myelitis
✓The underlying disease code must be sequenced first per coding guidelines
✓Imaging or laboratory evidence supporting the relationship

Commonly Confused Codes

•G04.89 — Other myelitis: use when myelitis is a primary diagnosis, not secondary to another classified disease
•G04.91 — Myelitis, unspecified: use when cause is unknown; G05.4 requires a known underlying disease
•G04.1 — Tropical spastic paraplegia: specific HTLV-1 associated myelitis has its own code
•G37.3 — Acute transverse myelitis in demyelinating disease: specific to demyelinating disease context