G05.4
BillableMyelitis in diseases classified elsewhere
Last updated: FY2026 ICD-10-CM (Oct 1, 2025 – Sep 30, 2026) | CMS-HCC V28 (100% phase-in, PY2026)
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
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 G05.4 to 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