G31.83
BillableNeurocognitive disorder with Lewy bodies
Last updated: FY2026 ICD-10-CM (Oct 1, 2025 – Sep 30, 2026) | CMS-HCC V28 (100% phase-in, PY2026)
Is G31.83 an HCC code?
Yes. G31.83 maps to Dementia, Mild or Unspecified 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 G31.83
For G31.83 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 G31.83 during that encounter — not just copy-forwarded from a problem list.
What This Code Means
G31.83 is the ICD-10-CM diagnosis code for neurocognitive disorder with lewy bodies. A type of dementia characterized by abnormal protein deposits called Lewy bodies in the brain, causing cognitive decline, movement problems, and behavioral changes. G31.83 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, G31.83 maps to Dementia, Mild or Unspecified (HCC 127) with a community, non-dual, aged base RAF weight of 0.464. G31.83 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.
Lewy body dementia often presents with Parkinson-like symptoms; code any movement disorders separately. Because G31.83 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 G31.83 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.
Coding Tips
- •Lewy body dementia often presents with Parkinson-like symptoms; code any movement disorders separately
- •Document hallucinations and behavioral symptoms as they are key diagnostic features
Clinical Significance
Neurocognitive disorder with Lewy bodies (Lewy body dementia) is the second most common type of progressive dementia after Alzheimer's disease. It is characterized by fluctuating cognition, visual hallucinations, and parkinsonism, creating complex management challenges. Accurate identification is critical because these patients are highly sensitive to antipsychotic medications, which can be life-threatening.
Documentation Requirements
- ✓Provider documentation specifically stating Lewy body dementia or neurocognitive disorder with Lewy bodies
- ✓Documentation of core clinical features: fluctuating cognition, recurrent visual hallucinations, and/or parkinsonism
- ✓Cognitive assessment results (MMSE, MoCA) showing progressive decline
- ✓REM sleep behavior disorder documentation if present (supportive feature)
- ✓Medication list noting sensitivity to neuroleptics/antipsychotics
- ✓Functional status assessment and care plan
Use Additional Code
- code, if applicable, to identify mild neurocognitive disorders due to known physiological condition (F06.7-)
Commonly Confused Codes
- •G30.0/G30.1/G30.9 — Alzheimer's disease; primarily memory loss without prominent hallucinations or parkinsonism
- •G20 — Parkinson's disease; when dementia develops after established Parkinson's, use G20 + F02.8x instead
- •G31.09 — Other frontotemporal neurocognitive disorder; behavioral/language variants without parkinsonism or hallucinations
- •F02.80/F02.81 — Dementia in other diseases; these are manifestation codes used alongside G31.83
- •G31.85 — Corticobasal degeneration; asymmetric motor findings without the hallucination feature