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G21.4 ICD-10-CM Code: Vascular parkinsonism

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

FY 2026 Apr update / Diseases of the nervous system (G00-G99) / Extrapyramidal and movement disorders (G20-G26)

G21.4

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

Vascular parkinsonism

Parkinson-like symptoms caused by stroke or reduced blood flow to areas of the brain that control movement.

Buddy the Bee presenting code insight

Buddy Insight

Vascular parkinsonism results from cerebrovascular disease affecting the basal ganglia, typically presenting with lower-body predominant symptoms ('lower half parkinsonism') after stroke or chronic small vessel disease.

CMS-HCC V28

HCC 199

RAF 0.0

CMS-HCC V24

HCC 78

RAF 0.584

ACA/HHS

0

0

RAF 0

ESRD/PACE

HCC 78

RAF 0.0

RXHCC

HCC 161

RAF 0.0

Code Trumping

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Code Book Path

Official
G21Secondary parkinsonism
G21.4Vascular parkinsonism

Inclusion Terms

Official

ICD-10-CM does not list inclusion terms for G21.4 in this effective period.

Excludes 2

Official

ICD-10-CM does not list Excludes 2 notes for G21.4 in this effective period.

Related Child Codes

Official
G21.0Malignant neuroleptic syndrome
G21.1Other drug-induced secondary parkinsonism
G21.2Secondary parkinsonism due to other external agents
G21.3Postencephalitic parkinsonism
G21.8Other secondary parkinsonism

Includes

Official

ICD-10-CM does not list Includes notes for G21.4 in this effective period.

Excludes 1

Official
  • Huntington's disease (G10)
  • neurocognitive disorder with Lewy bodies (G31.83)
  • Shy-Drager syndrome (G90.3)
  • syphilitic Parkinsonism (A52.19)

Code First

Official

ICD-10-CM does not list Code First sequencing instructions for G21.4 in this effective period.

Use Additional

Official

ICD-10-CM does not list Use Additional Code instructions for G21.4 in this effective period.

Code Also

Official

ICD-10-CM does not list Code Also instructions for G21.4 in this effective period.

Buddy Documentation Tip

HCC Buddy guidance
Brain imaging (MRI or CT) showing cerebrovascular disease affecting basal ganglia or subcortical white matter
Clinical presentation consistent with vascular parkinsonism (lower body predominant, gait freezing)
Documented cerebrovascular disease history (stroke, chronic small vessel disease, lacunar infarcts)
Poor or no response to levodopa (distinguishing feature from idiopathic Parkinson's disease)

MEAT Support

HCC Buddy guidance
Brain imaging (MRI or CT) showing cerebrovascular disease affecting basal ganglia or subcortical white matter
Clinical presentation consistent with vascular parkinsonism (lower body predominant, gait freezing)
Documented cerebrovascular disease history (stroke, chronic small vessel disease, lacunar infarcts)
Poor or no response to levodopa (distinguishing feature from idiopathic Parkinson's disease)

Audit Caution

HCC Buddy guidance
Coding idiopathic Parkinson's disease in a patient with imaging evidence of vascular parkinsonism
Not coding the underlying cerebrovascular disease (I63.x, I67.x) as an additional diagnosis
Failing to document the vascular risk factors that are driving the cerebrovascular disease
Confusing gait disorder from vascular parkinsonism with normal pressure hydrocephalus which has a similar presentation

Common Mistakes

HCC Buddy guidance
G20.A1-G20.C — Parkinson's disease: idiopathic, typically levodopa-responsive with upper extremity onset
I69.398 — Other sequelae of cerebral infarction: for post-stroke sequelae without specific parkinsonian features
G21.8 — Other secondary parkinsonism: for secondary causes other than vascular disease
G21.9 — Secondary parkinsonism, unspecified: less specific, should not be used when vascular etiology is confirmed

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 G21.4 an HCC code?

Yes. G21.4 maps to Parkinson and Huntington Diseases under the CMS-HCC V28 risk adjustment model (and Parkinson's and Huntington's Diseases under V24).

HCC Category Mapping

V28HCC 199, Parkinson and Huntington Diseases
0.000
V24HCC 78, Parkinson's and Huntington's Diseases
0.584
ESRDHCC 78, Parkinson's and Huntington's Diseases
0.000
RxHCCHCC 161, Parkinson's Disease and Other Movement Disorders
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 G21.4

For G21.4to 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 G21.4 during that encounter, not just copy-forwarded from a problem list.

What This Code Means

G21.4 is the ICD-10-CM diagnosis code for vascular parkinsonism. Parkinson-like symptoms caused by stroke or reduced blood flow to areas of the brain that control movement. G21.4 sits in the ICD-10-CM chapter for diseases of the nervous system (g00-g99), within the section covering extrapyramidal and movement disorders (g20-g26).

Under the CMS-HCC V28 risk adjustment model, G21.4 maps to Parkinson and Huntington Diseases (HCC 199) with a community, non-dual, aged base RAF weight of 0.000. Under the older CMS-HCC V24 model, G21.4 maps to Parkinson's and Huntington's Diseases (HCC 78) with a community, non-dual, aged base RAF weight of 0.584. 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.

Document the location and type of cerebrovascular disease contributing to the parkinsonism. Because G21.4 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 G21.4 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.

Coding Tips

  • •Document the location and type of cerebrovascular disease contributing to the parkinsonism
  • •Code the underlying cerebrovascular condition (I63, I64, etc.) separately

Clinical Significance

Vascular parkinsonism results from cerebrovascular disease affecting the basal ganglia, typically presenting with lower-body predominant symptoms ('lower half parkinsonism') after stroke or chronic small vessel disease. This diagnosis links cerebrovascular and movement disorder management, requiring treatment of both the vascular risk factors and the motor symptoms.

Documentation Requirements

  • ✓Brain imaging (MRI or CT) showing cerebrovascular disease affecting basal ganglia or subcortical white matter
  • ✓Clinical presentation consistent with vascular parkinsonism (lower body predominant, gait freezing)
  • ✓Documented cerebrovascular disease history (stroke, chronic small vessel disease, lacunar infarcts)
  • ✓Poor or no response to levodopa (distinguishing feature from idiopathic Parkinson's disease)
  • ✓Underlying cerebrovascular condition coded separately (I63.x, I67.x, etc.)
  • ✓Vascular risk factor assessment and management plan

Commonly Confused Codes

  • •G20.A1-G20.C: Parkinson's disease: idiopathic, typically levodopa-responsive with upper extremity onset
  • •I69.398: Other sequelae of cerebral infarction: for post-stroke sequelae without specific parkinsonian features
  • •G21.8: Other secondary parkinsonism: for secondary causes other than vascular disease
  • •G21.9: Secondary parkinsonism, unspecified: less specific, should not be used when vascular etiology is confirmed

Child Codes

G21.0Malignant neuroleptic syndrome
G21.1Other drug-induced secondary parkinsonism
G21.2Secondary parkinsonism due to other external agents
G21.3Postencephalitic parkinsonism
HCC 199
G21.4Vascular parkinsonism
HCC 199
G21.8Other secondary parkinsonism
HCC 199
G21.9Secondary parkinsonism, unspecified
HCC 199

Code Hierarchy

└G21Secondary parkinsonism└G21.4Vascular parkinsonism
└G21.4Vascular parkinsonism

Because G21.4 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.

G21.4 maps to CMS-HCC V28 category 199, Parkinson and Huntington Diseases. See the ICD-10 to HCC mapping hub for how the V28 crosswalk works.

Work G21.4 in HCC Buddy

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