2027 ICD-10-CM Diagnosis Code G21.4Vascular parkinsonism

ICD-10-CM Codes›G00–G99›G20-G26›G21

ICD-10-CM G21.4
CMSSource: CMS FY 2027 ICD-10-CM dataset · Effective Oct 1, 2026 – Sep 30, 2027

G21.4 is a billable ICD-10-CM diagnosis code for vascular parkinsonism. It is valid on HIPAA claims for fiscal year 2027 (October 1, 2026 through September 30, 2027) and groups to MS-DRG 56 through 57. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Other nervous system disorders (often hereditary or degenerative).

For Medicare Advantage risk adjustment, G21.4 maps to CMS-HCC Category 199 (Parkinson and Other Degenerative Disease of Basal Ganglia) under the V28 model, adding a risk factor of about 0.615 for a community, non-dual, aged beneficiary in payment year 2027.

Code Identity

ICD-10-CM Code
G21.4
Billable Status
Yes — Valid for Submission
Code Describes
Vascular parkinsonism
Short Description
Vascular parkinsonism
Same as the full description in the CMS dataset.
Parent Code
G21
Secondary parkinsonism

Code Classification

ChapterG00–G99Diseases of the nervous system
SectionG20-G26Extrapyramidal and movement disorders
CategoryG21Secondary parkinsonism
This CodeG21.4Vascular parkinsonism

Medicare Risk Adjustment (HCC)Billing

G21.4 maps to a payment category in the CMS-HCC model used to risk-adjust Medicare Advantage payments. Weights are the published community factors for payment year 2027.

CMS-HCC V28 Category (Payment Model)
HCC 199— Parkinson and Other Degenerative Disease of Basal Ganglia
Payment HCC · PY 2027 one of 16 ICD-10-CM codes in this category
Risk Adjustment Factor (RAF) Weight
+0.615
community, non-dual, aged · ranges 0.219–0.634 across segments
Hierarchy
Top of its hierarchy
HCC 199 is not superseded by any other condition category
Prior Model (CMS-HCC V24)
HCC 78
V24 retired V28 pays 100% of MA risk scores since PY 2026
Other CMS Models
PACE (CMS-HCC V22): HCC 78 · ESRD (V21): HCC 78 · ESRD (V24): HCC 78
ESRD V21 weights: 0.065 dialysis, 0.141–0.583 functioning graft · ESRD V24 weights: 0.079 dialysis, 0.206–0.608 functioning graft
Part D (RxHCC)
RxHCC 161 — Parkinson Disease
also risk-adjusts in the Part D prescription drug model (V08)

Source: CMS Payment Year 2027 risk adjustment mappings and model software. Weights are relative factors, not dollar amounts; a beneficiary's total RAF also includes demographics and interactions. Browse all CMS-HCC categories.

Approximate SynonymsGuidance

Alternate terms and clinical phrases that map to this code.

  • Vascular parkinsonism

Instructional NotesGuidance

Instructions from the official ICD-10-CM Tabular List that apply to G21.4: its own notes plus those printed at G21 and Chapter 6. A note printed at a category, block or chapter applies to every code under it.

Excludes1

Not coded here: the excluded code is never reported together with this one, unless the two conditions are unrelated.

From G21 Secondary parkinsonism applies to 8 codes
  • Huntington's disease (G10)
  • neurocognitive disorder with Lewy bodies (G31.83)
  • Shy-Drager syndrome (G90.3)
  • syphilitic Parkinsonism (A52.19)

Excludes2

Not included here: the excluded condition is not part of this code, but a patient may have both, so both codes may be reported.

From Chapter 6 (G00-G99) Diseases of the nervous system applies to 700 codes
  • certain conditions originating in the perinatal period (P04-P96)
  • certain infectious and parasitic diseases (A00-B99)
  • complications of pregnancy, childbirth and the puerperium (O00-O9A)
  • congenital malformations, deformations, and chromosomal abnormalities (Q00-Q99)
  • endocrine, nutritional and metabolic diseases (E00-E88)
  • injury, poisoning and certain other consequences of external causes (S00-T88)
  • neoplasms (C00-D49)
  • symptoms, signs and abnormal clinical and laboratory findings, not elsewhere classified (R00-R94)

Source: CMS ICD-10-CM Tabular List. How to read instructional notes.

Referenced in Other NotesGuidance

Instructional notes printed at other codes that name G21.4, its category, or a range that includes it.

Excludes1 2

These codes carry an Excludes1 note naming G21.4: they are not reported together with it, unless the two conditions are unrelated.

  • G20.C Parkinsonism, unspecified
    secondary parkinsonism (G21.-) names G21.-, which includes this code
  • R25 Abnormal involuntary movements
    specific movement disorders (G20-G26) names G20-G26, which includes this code

Excludes2 1

These codes carry an Excludes2 note naming G21.4: its condition is not part of those codes, and both may be reported when the patient has both.

  • F98.4 Stereotyped movement disorders
    movement disorders of organic origin (G20-G25) names G20-G25, which includes this code

Index to Diseases and InjuriesGuidance

Alphabetical index entries that point to this code.

Clinical ClassificationClinical

AHRQ’s CCSR groups this code into broader clinical categories.

CCSR NVS006
Other nervous system disorders (often hereditary or degenerative)
Default principal diagnosis: inpatient Yes · outpatient Yes

Clinical InformationClinical

  • Parkinson Disease, Secondary

    conditions which feature clinical manifestations resembling primary parkinson disease that are caused by a known or suspected condition. examples include parkinsonism caused by vascular injury, drugs, trauma, toxin exposure, neoplasms, infections and degenerative or hereditary conditions. clinical features may include bradykinesia, rigidity, parkinsonian gait, and masked facies. in general, tremor is less prominent in secondary parkinsonism than in the primary form. (from joynt, clinical neurology, 1998, ch38, pp39-42)

Patient EducationClinical

Parkinson's Disease

Parkinson's disease (PD) is a type of movement disorder. It happens when nerve cells in the brain don't produce enough of a brain chemical called dopamine. Sometimes it is genetic, but most cases do not seem to run in families. Exposure to chemicals in the environment might play a role.

Read the full article at MedlinePlus

Courtesy of MedlinePlus, a service of the U.S. National Library of Medicine.

Convert G21.4 to ICD-9-CMHistory

The closest ICD-9-CM equivalents under the General Equivalence Mappings.

ICD-9-CM
332.0 Paralysis agitans
Approximate The match is approximate rather than exact.

Code HistoryHistory

FY 2016AddedAdded to the ICD-10-CM code setEffective October 1, 2015, the first year of ICD-10-CM.
FY 2017–2026No changes
FY 2027CurrentCurrent code set, no changesEffective October 1, 2026 through September 30, 2027.

Questions About G21.4Overview

What is the ICD-10 code for vascular parkinsonism?

The ICD-10-CM code for vascular parkinsonism is G21.4 (sometimes written as G214). It is billable on HIPAA-covered claims from October 1, 2026 through September 30, 2027.

Is G21.4 (Secondary parkinsonism) a billable code?

Yes. This is a billable ICD-10-CM code, specific enough to report vascular parkinsonism on HIPAA-covered claims from October 1, 2026 through September 30, 2027.

What MS-DRG does G21.4 group to?

When vascular parkinsonism is the principal diagnosis on an inpatient stay, it groups to MS-DRG 57, 56, with relative weights from 1.2835 to 2.2649 depending on complications. Higher weights mean higher Medicare reimbursement.

Can G21.4 be reported with G10?

Not as a rule. The Excludes1 note at G21, which applies to G21.4, lists "Huntington's disease (G10)". An Excludes1 note means the excluded code is never reported together with this one; the only exception is when the two conditions are unrelated to each other (Official Guidelines, Section I.A.12.a).

What is the ICD-9 equivalent of G21.4?

Under the General Equivalence Mappings, vascular parkinsonism converts to ICD-9-CM 332.0 (paralysis agitans). The mapping is approximate, so confirm the match fits the documentation.

What HCC is G21.4?

G21.4 (vascular parkinsonism) maps to CMS-HCC Category 199 (Parkinson and Other Degenerative Disease of Basal Ganglia), commonly written as HCC 199, in the CMS-HCC V28 model used for Medicare Advantage risk adjustment in payment year 2027. It mapped to HCC 78 under the retired V24 model. It also maps in the PACE (CMS-HCC V22), ESRD (V21), and ESRD (V24) models. In the Part D prescription drug model it maps to RxHCC 161.

Does G21.4 risk-adjust for Medicare Advantage payment?

Yes. When documented and reported on a Medicare Advantage encounter, G21.4 adds a risk adjustment factor of about 0.615 to the beneficiary's RAF score for a community, non-dual, aged enrollee (published V28 weights range from 0.219 to 0.634 depending on the payment segment). HCC 199 sits at the top of its hierarchy, so no other condition category supersedes it. See the full factor table on the HCC 199 category page.