2027 ICD-10-CM Diagnosis Code G23.2Striatonigral degeneration

ICD-10-CM Codes›G00–G99›G20-G26›G23

ICD-10-CM G23.2
CMSSource: CMS FY 2027 ICD-10-CM dataset · Effective Oct 1, 2026 – Sep 30, 2027

G23.2 is a billable ICD-10-CM diagnosis code for striatonigral degeneration. 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. As a secondary diagnosis, it counts as a complication or comorbidity (CC) and moves an inpatient stay to a higher severity level within its MS-DRG family. It does not count, however, when the principal diagnosis is one of 23 closely related codes. Coders also document this condition as familial infantile bilateral striatal necrosis. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Other nervous system disorders (often hereditary or degenerative).

For Medicare Advantage risk adjustment, G23.2 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
G23.2
Billable Status
Yes — Valid for Submission
Code Describes
Striatonigral degeneration
Short Description
Striatonigral degeneration
Same as the full description in the CMS dataset.
Parent Code
G23
Other degenerative diseases of basal ganglia

Code Classification

ChapterG00–G99Diseases of the nervous system
SectionG20-G26Extrapyramidal and movement disorders
CategoryG23Other degenerative diseases of basal ganglia
This CodeG23.2Striatonigral degeneration

Medicare Risk Adjustment (HCC)Billing

G23.2 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HCC 199 is not superseded by any other condition category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.

  • Familial infantile bilateral striatal necrosis
  • Infantile striatonigral degeneration
  • Sporadic infantile bilateral striatal necrosis
  • Striatonigral degeneration

Instructional NotesGuidance

Instructions from the official ICD-10-CM Tabular List that apply to G23.2: its own notes plus those printed at G23 and Chapter 6. A note printed at a category, block or chapter applies to every code under it.

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 G23 Other degenerative diseases of basal ganglia applies to 6 codes
  • multi-system degeneration of the autonomic nervous system (G90.3)
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 G23.2, its category, or a range that includes it.

Excludes1 1

These codes carry an Excludes1 note naming G23.2: they are not reported together with it, unless the two conditions are unrelated.

  • 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 G23.2: 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

  • Striatonigral Degeneration

    a sporadic neurodegenerative disease with onset in middle-age characterized clinically by parkinsonian features (e.g., muscle rigidity; hypokinesia; stooped posture) and hypotension. this condition is considered a clinical variant of multiple system atrophy. pathologic features include a prominent loss of neurons in the zona compacta of the substantia nigra and putamen. (from adams et al., principles of neurology, 6th ed, p1075-6)

Patient EducationClinical

Degenerative Nerve Diseases

Degenerative nerve diseases affect many of your body's activities, such as balance, movement, talking, breathing, and heart function. Many of these diseases are genetic. Sometimes the cause is a medical condition such as alcoholism, a tumor, or a stroke. Other causes may include toxins, chemicals, and viruses.

Read the full article at MedlinePlus

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

Convert G23.2 to ICD-9-CMHistory

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

ICD-9-CM
333.0 Degen basal ganglia NEC
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 G23.2Overview

What is the ICD-10 code for striatonigral degeneration?

The ICD-10-CM code for striatonigral degeneration is G23.2 (sometimes written as G232). It is billable on HIPAA-covered claims from October 1, 2026 through September 30, 2027.

Is G23.2 (Other degenerative diseases of basal ganglia) a billable code?

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

What MS-DRG does G23.2 group to?

When striatonigral degeneration 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.

Is G23.2 a CC or MCC?

CMS lists G23.2 as a CC (complication or comorbidity) for FY 2027. Reported as a secondary diagnosis, it moves the inpatient stay to a higher-weighted DRG within its severity family. It does not count when the principal diagnosis is one of the 23 closely related codes in its exclusion list.

What is the ICD-9 equivalent of G23.2?

Under the General Equivalence Mappings, striatonigral degeneration converts to ICD-9-CM 333.0 (degen basal ganglia NEC). The mapping is approximate, so confirm the match fits the documentation.

What HCC is G23.2?

G23.2 (striatonigral degeneration) 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 G23.2 risk-adjust for Medicare Advantage payment?

Yes. When documented and reported on a Medicare Advantage encounter, G23.2 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.