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G20.C ICD-10-CM Code: Parkinsonism, unspecified

Billing Status: YES. This is a valid, specific, and billable ICD-10-CM reference.

Coding at a Glance

Tabular directives
1 inclusion term · 4 Excludes1 · 7 use-additional codes
Risk adjustment
CMS-HCC V28: 1 category · CMS-HCC V22 category 78 · RxHCC V08 category 161

Inpatient Payment Groups (MS-DRG)

Potential MS-DRG participation — not a DRG assignment.

MS-DRGs this diagnosis helps define, as principal or secondary, per the CMS ICD-10-CM/PCS MS-DRG Definitions Manual v43, Appendix B.

  • MS-DRG 056 — DEGENERATIVE NERVOUS SYSTEM DISORDERS WITH MCC (MDC 01)
  • MS-DRG 057 — DEGENERATIVE NERVOUS SYSTEM DISORDERS WITHOUT MCC (MDC 01)

A diagnosis appearing in a group's logic does not by itself determine the DRG assigned to a stay; the grouper uses the full claim.

Risk Adjustment (CMS-HCC)

Payment categories this diagnosis maps to under CMS-HCC V28, payment year 2026.

  • HCC 199 — Parkinson and Other Degenerative Disease of Basal Ganglia

Other models: CMS-HCC V22 HCC 78 · RxHCC V08 HCC 161

Risk scores depend on the enrollee's full accepted diagnosis set and segment; a category mapping alone does not determine payment.

Coding instructions

Official Tabular Instructional Notes: the inclusion, exclusion and sequencing notes published for G20.C in the official ICD-10-CM tabular list, quoted as published.

Source: CMS/CDC — ICD-10-CM Tabular ListRelease: FY2026Effective: October 1, 2025

Notes without a marker are published on G20.C itself; “inherited from” names the category or block whose note applies here.

Inclusion Terms

Alternative terms the tabular list files under this code.

  • Parkinsonism, NOS

Excludes1 — Not Coded Here

Conditions generally not reported together with this code (Excludes1) -- an error unless the two conditions are documented as unrelated to each other (ICD-10-CM Official Guidelines, Section I.A.12.a).

Use Additional Code

Supplementary codes the tabular list directs you to add.

Source: inherited from G20

Coder workflow for G20.C

MedCoder structured workflow — derived from this code’s own official record

Before you code G20.C

  1. Unspecified does not mean incorrect. When the record gives no greater specificity, G20.C may be the appropriate code. Check the record for detail that supports a more specific sibling — in this subcategory the siblings differ by the presence or absence of the associated condition. An unspecified code is for records that do not provide the detail a more specific code needs; a query, not an assumption, is the route to specificity (Guidelines I.A.9.b, I.B.18).

    ReviewG20.A, G20.B

    See the relationships section · Guide: Other vs unspecified (NEC vs NOS) →

  2. Check the Excludes1 note: if the documentation supports a condition named there, do not simply proceed with G20.C. Excludes1 conditions are not reported together with this code unless the record shows they are unrelated (Guidelines I.A.12.a).

    See the official tabular notes

Choose the right path

  1. Does the record document the detail a more specific sibling code needs?
    Yes → Review the specific siblings in this subcategory.
    No → Continue — G20.C is appropriate when the documentation goes no further.

    ReviewG20.A, G20.B

  2. Does the documentation support a condition named in G20.C’s Excludes1 note?
    Yes → Do not simply proceed: review the excluded code. Both are reported only when the record shows the two conditions are unrelated.
    No → Continue.

    ReviewG20.A1, G20.B, G20.A, G21

Consider G20.C. Then work the Use Additional Code note, and confirm the code is valid for the date of service in the Verify section.

Documentation check

The provider’s diagnostic statement
Codes are assigned from the provider’s documented diagnosis, not from clinical criteria, test values or a medication list (Guidelines I.A.19).
The associated condition or complication
Whether the associated condition the title names is documented; the “with” convention presumes some links, and a provider statement that the conditions are unrelated defeats it (Guidelines I.A.15).
The conditions the Use Additional Code note names
Reported with this code when documented; a conditional instruction (“if applicable”, “if known”) applies only when the record supports it.
Any detail beyond this code’s title
What the record states that a more specific sibling code would capture — or its absence, which itself supports the unspecified code.

Official instructions as workflow

  • Excludes1 — check before selecting G20.C(4 notes)

    Coding workflow: If the documentation supports a condition named in this note, do not simply proceed with G20.C: the two are not reported together. The one exception is when the record shows the two conditions are unrelated to each other.

    CompareG20.A1, G20.B, G20.A, G21

    See the official tabular notes · Guidelines I.A.12.a

  • Use Additional Code — after identifying G20.C(7 notes)

    Coding workflow: Check whether the documentation supports the additional code(s) the note names, and report them with G20.C when it does. Where the instruction is conditional (“if applicable”, “if known”), it applies only when the record documents the condition.

    ReviewF02.84, F02.A4, F02.B4, F02.C4, F02.81, F02.A1

    See the official tabular notes · Guidelines I.A.13

Coding decision scenarios

Pattern scenarios for this code’s structure — decision rules, not clinical cases

Documentation: The provider documents the condition in the terms of this code’s title and records no further detail.

Coding question: Is a more specific sibling code supportable?

Path: Review the specific siblings in this subcategory and what each requires the record to state.

Reason: A more specific code needs documentation of the distinguishing element; without it the unspecified code is appropriate, and a provider query is the route to specificity (Guidelines I.A.9.b, I.B.18).

ReviewG20.A, G20.B

Documentation: Both the condition G20.C describes and a condition named in its Excludes1 note are documented for the same encounter.

Coding question: Can both codes be reported?

Path: Review the Excludes1 note and the excluded code, and look for a provider statement on whether the two conditions are related.

Reason: Excludes1 means the two are not coded together; the exception is when the record shows the conditions are unrelated to each other (Guidelines I.A.12.a).

ReviewG20.A1, G20.B, G20.A, G21

Documentation: A condition the Use Additional Code note names is documented.

Coding question: Is a second code reported with G20.C?

Path: Review the Use Additional Code note and the code it names.

Reason: The additional code is reported when the record documents the condition; a conditional instruction applies only when its condition is met (Guidelines I.A.13).

ReviewF02.84, F02.A4, F02.B4, F02.C4, F02.81, F02.A1

Every row is derived from this code’s own record — its title, tabular notes, 7th-character family and same-category siblings — with fixed MedCoder wording; nothing is inferred about a patient. The official notes and guideline text are in the sections each row links to, and they control.

Code Overview

Parkinsonism, unspecified is a billable ICD-10-CM diagnosis code (G20.C).

MedCoder summary Summary composed by MedCoder from this code's official ICD-10-CM record. The tabular instructional notes themselves appear verbatim below.

Indexed Clinical Terms (11)

Official source data — entries quoted as published, in the Index’s own lookup phrasing

Clinical term phrases from the official ICD-10-CM Index to Diseases and Injuries that map to this code. These are alphabetic-index entries shown as the Index writes them — lookup phrasing, not necessarily the wording of a final diagnosis.

Verify Before Coding

  • No Medicare Code Editor or MS-DRG Definitions Manual restrictions apply to this code.

From the code registry, the Medicare Code Editor, and the MS-DRG Definitions Manual. Check it against a full claim in Claim Check.

Relationships & Classification

MedCoder structured relationships — computed from published CMS and AHRQ datasets

Other codes that name G20.C or its code family, from the CMS ICD-10-CM tabular instructional notes. Tabular-note edges are stored at the code family level that carries each note.

Referenced by 1 Excludes1 note: R25 — Abnormal involuntary movements (via G20.-).

These codes’ tabular lists mark this diagnosis as mutually exclusive — not reported together unless the conditions are documented as unrelated.

Referenced by 1 Excludes2 note: F98.4 — Stereotyped movement disorders (via G20.-).

These codes’ tabular lists name this diagnosis as distinct — both may be reported when both are documented.

Referenced by 3 Code First instructions across 2 chapters: F02 — Dementia in other diseases classified elsewhere (via G20.-), F06.7 — Mild neurocognitive disorder due to known physiological condition (via G20.-), R47.82 — Fluency disorder in conditions classified elsewhere (via G20.-).

Each of these codes carries a Code First note naming this condition — when that code is reported, THIS code is sequenced first, ahead of it.

MS-DRG Grouper Relationships (FY2026)

Potential MS-DRG participation — not a DRG assignment.

FY2026 MS-DRG: not on the CMS CC/MCC list — as a secondary diagnosis this code does not change MS-DRG severity for that release.

Named in the grouper logic of 2 MS-DRGs: DRG 056 (MDC 01), DRG 057 (MDC 01).

From the CMS MS-DRG Definitions Manual (Appendices B and C). Actual DRG assignment depends on the complete claim.

Clinical classification (AHRQ CCSR):NVS004 — Parkinson's disease (default).

Clinical Classifications Software Refined (CCSR) for ICD-10-CM Diagnoses. Healthcare Cost and Utilization Project (HCUP), Agency for Healthcare Research and Quality.

Related Codes

Same CMS-HCC risk category (V28)

CMS maps these diagnoses to the same Hierarchical Condition Category (Parkinson and Other Degenerative Disease of Basal Ganglia) for risk-adjusted payment.

G20.A1 — Parkinson's disease without dyskinesia, without mention of fluctuations, G20.A2 — Parkinson's disease without dyskinesia, with fluctuations, G20.B1 — Parkinson's disease with dyskinesia, without mention of fluctuations, G20.B2 — Parkinson's disease with dyskinesia, with fluctuations, G21.3 — Postencephalitic parkinsonism, G21.4 — Vascular parkinsonism, G21.8 — Other secondary parkinsonism, G21.9 — Secondary parkinsonism, unspecified, G23.0 — Hallervorden-Spatz disease, G23.1 — Progressive supranuclear ophthalmoplegia [Steele-Richardson-Olszewski], G23.2 — Striatonigral degeneration, G23.3 — Hypomyelination with atrophy of the basal ganglia and cerebellum, G23.8 — Other specified degenerative diseases of basal ganglia, G23.9 — Degenerative disease of basal ganglia, unspecified, G90.3 — Multi-system degeneration of the autonomic nervous system

Same clinical category (CCSR)

AHRQ's Clinical Classifications Software groups these diagnoses under the same clinical category (Parkinson's disease).

G20 — Parkinson's disease, G20.A1 — Parkinson's disease without dyskinesia, without mention of fluctuations, G20.A2 — Parkinson's disease without dyskinesia, with fluctuations, G20.B1 — Parkinson's disease with dyskinesia, without mention of fluctuations, G20.B2 — Parkinson's disease with dyskinesia, with fluctuations

Same Index main term, other category

The ICD-10-CM Index to Diseases and Injuries files this code under the main terms “Parkinsonism”, “Paralysis, paralytic”, “Dementia”; these codes share that main term but sit in a different category of the Tabular List.

F44.89 — Other dissociative and conversion disorders (accommodation, hysterical), F84.3 — Other childhood disintegrative disorder (infantile, infantilis), G10 — Huntington's disease (in, Huntington's disease or chorea), G11.4 — Hereditary spastic paraplegia (familial, spastic), G11.9 — Hereditary ataxia, unspecified (ataxic), G12.21 — Amyotrophic lateral sclerosis (amyotrophic), G12.22 — Progressive bulbar palsy (bulbar), G12.23 — Primary lateral sclerosis (lateral), G12.25 — Progressive spinal muscle atrophy (spinal, progressive, muscle), G12.29 — Other motor neuron disease (wasting), G21.11 — Neuroleptic induced parkinsonism (neuroleptic induced), G21.19 — Other drug induced secondary parkinsonism (due to, drugs NEC), G21.2 — Secondary parkinsonism due to other external agents (secondary, due to, external agents NEC), G21.3 — Postencephalitic parkinsonism (postencephalitic), G21.4 — Vascular parkinsonism (vascular), G21.8 — Other secondary parkinsonism (secondary, specified NEC), G21.9 — Secondary parkinsonism, unspecified (secondary), G23.1 — Progressive supranuclear ophthalmoplegia [Steele-Richardson-Olszewski] (supranuclear), G31.01 — Pick's disease (in, Pick's), G31.09 — Other frontotemporal neurocognitive disorder (frontal), +191 more

Contextual Map

Every relationship of G20.C in one view: hierarchy, official tabular instructions in both directions, clinical classification, risk adjustment, MS-DRG participation, index terms and change history — each edge carrying the CMS source it derives from.

Run G20.C with these 9 related codes in Claim Check

Hierarchy

Excludes1

Referenced by Excludes1 notes

Referenced by Excludes2 notes

Referenced by Code First instructions

Clinical classification (CCSR)

Risk adjustment (CMS-HCC)

  • HCC 199 — Parkinson and Other Degenerative Disease of Basal Ganglia [CMS-HCC]— CMS-HCC V28 · 2026

MS-DRG Grouper

MDC crossing

  • MDC 01 — Diseases and Disorders of the Nervous System[MDC crossing]: “Diseases and Disorders of the Nervous System — the grouper's crossing between diagnoses and procedures: a principal diagnosis sets the MDC, and same-MDC procedures move the stay to its surgical DRGs. 8,892 same-MDC procedures group here; browse them on the MDC page.”— CMS MS-DRG Definitions Manual · FY2026

Index entries (11)

  • Dementia (degenerative (primary)) (persisting) (unspecified severity) (without behavioral disturbance, psychotic disturbance, mood disturbance, and anxiety), in (due to), paralysis agitans[Index term]— CMS ICD-10-CM Index to Diseases and Injuries · icd10cm-fy2026
  • Dementia (degenerative (primary)) (persisting) (unspecified severity) (without behavioral disturbance, psychotic disturbance, mood disturbance, and anxiety), in (due to), paralysis agitans, with behavioral disturbance[Index term]— CMS ICD-10-CM Index to Diseases and Injuries · icd10cm-fy2026
  • Dementia (degenerative (primary)) (persisting) (unspecified severity) (without behavioral disturbance, psychotic disturbance, mood disturbance, and anxiety), with, Parkinsonism[Index term]— CMS ICD-10-CM Index to Diseases and Injuries · icd10cm-fy2026
  • Dementia (degenerative (primary)) (persisting) (unspecified severity) (without behavioral disturbance, psychotic disturbance, mood disturbance, and anxiety), with, Parkinsonism, with behavioral disturbance[Index term]— CMS ICD-10-CM Index to Diseases and Injuries · icd10cm-fy2026
  • Hemiparkinsonism[Index term]— CMS ICD-10-CM Index to Diseases and Injuries · icd10cm-fy2026
  • Paralysis, paralytic (complete) (incomplete), agitans[Index term]— CMS ICD-10-CM Index to Diseases and Injuries · icd10cm-fy2026
  • Parkinsonism (idiopathic) (primary)[Index term]— CMS ICD-10-CM Index to Diseases and Injuries · icd10cm-fy2026
  • Parkinsonism (idiopathic) (primary), dementia[Index term]— CMS ICD-10-CM Index to Diseases and Injuries · icd10cm-fy2026
  • and 3 more

Nearest codes

Change history

Sources for this page

Codes, titles, notes, index terms and mappings on this page are transcribed from the datasets below. Relationships MedCoder computed and text MedCoder wrote are labelled where they appear.

Code, title, tabular notes and index terms Official source data
CMS/CDC ICD-10-CM FY2026 tabular list, index and tables, effective October 1, 2025 Release, file and checksum · Publisher’s page
Claim edits Official source data
CMS Definitions of Medicare Code Edits — v43.1 (April 2026) Release, file and checksum · Publisher’s page
Inpatient payment groups Official source data
CMS MS-DRG Definitions Manual (incl. Appendix B diagnosis index, Appendix C CC/MCC list, Appendix E procedure index) and IPPS Final Rule tables — v43 Release, file and checksum · Publisher’s page
Risk adjustment Official source data
2026 Mid-Year Final ICD-10 Mappings + Model Software (cms.gov/files/zip/2026-midyear-final-icd-10-mappings.zip, 2026-midyear-final-model-software.zip) — CMS-HCC V28, PY2026 mid-year final release Release, file and checksum · Publisher’s page
Change history and date-of-service validity Official source data
CMS ICD-10-CM release addenda, ingested release by release into the change ledger Release, file and checksum · Publisher’s page
Comparisons, relationships and the contextual map MedCoder structured relationship
Computed by MedCoder from the tabular notes and tables above; every derived relationship is marked as derived where it appears
Summary and FAQ answers MedCoder explanation
Written by MedCoder to explain the sources above: drafted with AI assistance, checked by a person against the release files, and labelled as MedCoder text where it appears. Not official text.

Labels on this page: Official source data · MedCoder structured relationship · MedCoder explanation. How to read the labels · All data sources and release dates

Cite this page

Reference this page in a research guide, syllabus or article. The release is included because code content changes each year.

MedCoder.ai. "G20.C — Parkinsonism, unspecified." ICD-10-CM FY2026. https://medcoder.ai/icd10/code/g20.c-parkinsonism-unspecified

Change history

  • FY2024 — October 1, 2023
    Added to the code set
    Parkinsonism, unspecified
    FY2024 changes

Nearest Codes in This Family

Official ICD-10-CM classifications closest to G20.C in its code family, with their registry titles.

View all codes in the G20 family