G37.9
BillableDemyelinating disease of central nervous system, unspecified
Last updated: FY2026 ICD-10-CM (Oct 1, 2025 – Sep 30, 2026) | CMS-HCC V28 (100% phase-in, PY2026)
Is G37.9 an HCC code?
Yes. G37.9 maps to Multiple Sclerosis under the CMS-HCC V28 risk adjustment model (and Multiple Sclerosis 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 G37.9
For G37.9 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 G37.9 during that encounter — not just copy-forwarded from a problem list.
What This Code Means
G37.9 is the ICD-10-CM diagnosis code for demyelinating disease of central nervous system, unspecified. A condition involving damage to nerve insulation in the brain and spinal cord where the specific type has not been determined or specified. G37.9 sits in the ICD-10-CM chapter for diseases of the nervous system (g00-g99), within the section covering demyelinating diseases of the central nervous system (g35-g37).
Under the CMS-HCC V28 risk adjustment model, G37.9 maps to Multiple Sclerosis (HCC 198) with a community, non-dual, aged base RAF weight of 0.000. Under the older V24 model, G37.9 mapped to the same category but with a base RAF weight of 0.476 — 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.
This is an unspecified code; use only when the specific demyelinating disease cannot be determined from documentation. Because G37.9 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 G37.9 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.
Coding Tips
- •This is an unspecified code; use only when the specific demyelinating disease cannot be determined from documentation
- •Query the provider for more specific diagnosis if possible to assign a more precise code from the G37 category
Clinical Significance
Demyelinating disease of the central nervous system, unspecified, is used when a patient has a confirmed CNS demyelinating condition but the specific type has not been determined. This represents a significant documentation improvement opportunity, as identifying the specific demyelinating disease affects treatment decisions and prognosis. It still captures the condition for risk adjustment purposes.
Documentation Requirements
- ✓Documentation confirming a demyelinating disease of the CNS is present
- ✓Neuroimaging supporting the demyelinating nature of the condition
- ✓Evidence that diagnostic workup is ongoing or that specific diagnosis could not be determined
- ✓Neurological examination documenting deficits consistent with CNS demyelination
- ✓Plan for further diagnostic evaluation (antibody testing, follow-up MRI)
Commonly Confused Codes
- •G35 — Multiple sclerosis; should be used when MS diagnostic criteria are met
- •G37.89 — Other specified demyelinating diseases of CNS; use when a specific type is identified
- •G36.0 — Neuromyelitis optica; requires antibody testing to confirm
- •G37.81 — MOGAD; requires MOG antibody testing to confirm
- •R29.818 — Other symptoms and signs involving the nervous system; use for symptoms, not confirmed demyelinating disease