2026 ICD-10-CM Diagnosis Code G21.2Secondary parkinsonism due to other external agents

ICD-10-CM Codes›G00–G99›G20-G26›G21

ICD-10-CM G21.2
CMSSource: CMS FY 2026 ICD-10-CM dataset · Effective Oct 1, 2025 – Sep 30, 2026

G21.2 is a billable ICD-10-CM diagnosis code for secondary parkinsonism due to other external agents. It is valid on HIPAA claims for fiscal year 2026 (October 1, 2025 through September 30, 2026). Coders also document this condition as carbon monoxide encephalopathy. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Other nervous system disorders (often hereditary or degenerative).

Code Identity

ICD-10-CM Code
G21.2
Billable Status
Yes — Valid for Submission
Code Describes
Secondary parkinsonism due to other external agents
Short Description
Secondary parkinsonism due to other external agents
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 CodeG21.2Secondary parkinsonism due to other external agents

Approximate SynonymsGuidance

Alternate terms and clinical phrases that map to this code.

  • Carbon monoxide encephalopathy
  • Carbon monoxide-induced parkinsonism
  • MPTP-induced parkinsonism
  • Parkinsonism caused by carbon disulfide
  • Parkinsonism caused by cyanide
  • Pesticide-induced Parkinsonism
  • Toxin-induced parkinsonism

Tabular List NotesGuidance

Coding notes and annotation back-references applicable to this code.

Code First

Index to Diseases and InjuriesGuidance

Alphabetical index entries that point to this code.

External Cause of Injuries IndexGuidance

References for this code in the External Cause of Injuries Index.

    • Parkinsonism(idiopathic) (primary)
      • secondary
        • due to
          • external agents NEC

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

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 G21.2 to ICD-9-CMHistory

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

ICD-9-CM
332.1 Secondary parkinsonism
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 2017–2025No changes
FY 2026CurrentCurrent code set, no changesEffective October 1, 2025 through September 30, 2026.

Questions About G21.2Overview

Is G21.2 (Secondary parkinsonism) a billable code?

Yes. This is a billable ICD-10-CM code, specific enough to report secondary parkinsonism due to other external agents on HIPAA-covered claims from October 1, 2025 through September 30, 2026.

What is the ICD-9 equivalent of G21.2?

Under the General Equivalence Mappings, secondary parkinsonism due to other external agents converts to ICD-9-CM 332.1 (secondary parkinsonism). The mapping is approximate, so confirm the match fits the documentation.

Footnotes

[1] Chronic - a chronic condition code indicates a condition lasting 12 months or longer and its effect on the patient based on one or both of the following criteria:

  • The condition results in the need for ongoing intervention with medical products,treatment, services, and special equipment
  • The condition places limitations on self-care, independent living, and social interactions.