G31.80
BillableLeukodystrophy, unspecified
Last updated: FY2026 ICD-10-CM (Oct 1, 2025 – Sep 30, 2026) | CMS-HCC V28 (100% phase-in, PY2026)
Is G31.80 an HCC code?
Yes. G31.80 maps to Cerebellar Ataxia and Other Degenerative Diseases of Nervous System under the CMS-HCC V28 risk adjustment model.
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 G31.80
For G31.80 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 G31.80 during that encounter — not just copy-forwarded from a problem list.
What This Code Means
G31.80 is the ICD-10-CM diagnosis code for leukodystrophy, unspecified. A group of inherited disorders affecting the white matter of the brain, causing progressive neurological deterioration without a specific identified type. G31.80 sits in the ICD-10-CM chapter for diseases of the nervous system (g00-g99), within the section covering other degenerative diseases of the nervous system (g30-g32).
Under the CMS-HCC V28 risk adjustment model, G31.80 maps to Cerebellar Ataxia and Other Degenerative Diseases of Nervous System (HCC 200) with a community, non-dual, aged base RAF weight of 0.262. G31.80 was not retained as a payment HCC under the older V24 model, so V28 introduced or recategorized it during the 2024–2026 phase-in. 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.
Leukodystrophies are rare genetic disorders; query for specific type if documentation is vague. Because G31.80 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 G31.80 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.
Coding Tips
- •Leukodystrophies are rare genetic disorders; query for specific type if documentation is vague
- •Consider genetic testing documentation and family history when coding these conditions
Clinical Significance
Leukodystrophy, unspecified, captures a group of rare inherited disorders affecting the white matter of the brain. These conditions cause progressive neurological deterioration and require intensive multidisciplinary care. Despite being unspecified, the diagnosis reflects a serious genetic neurological condition with significant care needs and resource utilization.
Documentation Requirements
- ✓Documentation confirming leukodystrophy diagnosis via neuroimaging (MRI showing white matter abnormalities)
- ✓Genetic testing results if available, even if specific type is not identified
- ✓Neurological examination findings documenting motor, cognitive, or developmental deficits
- ✓Documentation that specific leukodystrophy subtypes could not be determined
- ✓Family history of neurological disorders if applicable
- ✓Current treatment plan and specialty referrals