October 1 update. Our PDGM and ICD-10 tools now use the FY2027 code set: 190 codes added, 30 deleted, and no existing code changed clinical group.

See what changed

ICD-10 · PDGM grouping

G21 Secondary parkinsonism

All 8 codes in the G21 family, with the PDGM clinical group, comorbidity subgroup and primary-position rule CMS assigns, read from the CMS grouper crosswalk v07.2.26 and the CDC FY2027 code file.

ICD-10-CM FY2027 · CMS grouper v07.2.26

Codes in family

8

Can lead a claim

7

Cannot lead a claim

1

What CMS assigns to G21

7 of the 8 codes group to Neuro Rehabilitation; 1 is assigned no clinical group. 7 of the 8 count toward the Spinal Muscular Atrophy, Systemic atrophy and Motor Neuron Disease comorbidity subgroup; 1 is assigned none. 7 of the 8 can lead a claim. CMS attaches a code-first note to 1 of the 8.

  • Spinal Muscular Atrophy, Systemic atrophy and Motor Neuron Disease: can award the low comorbidity tier as a secondary diagnosis.

Code first

CMS grouper convention 8, on G21.2. Code first:

  • , if applicable, toxic effects of substances chiefly nonmedicinal as to source (T51-T65)

Every code in G21

Descriptions are CDC’s FY2027 wording; where CMS’s grouper abbreviates one, its form is shown beneath.

CodeDescriptionPrimary positionClinical groupComorbidity subgroup
G21.0Malignant neuroleptic syndromeCan lead a claimBNone
G21.1 Other drug-induced secondary parkinsonism
G21.11Neuroleptic induced parkinsonismCan lead a claimBSpinal Muscular Atrophy, Systemic atrophy and Motor Neuron Disease
G21.19Other drug induced secondary parkinsonismCan lead a claimBSpinal Muscular Atrophy, Systemic atrophy and Motor Neuron Disease
G21.2Secondary parkinsonism due to other external agentsCannot lead a claimPrincipal diagnosis not assigned to a clinical groupNoneSpinal Muscular Atrophy, Systemic atrophy and Motor Neuron Disease
G21.3Postencephalitic parkinsonismCan lead a claimBSpinal Muscular Atrophy, Systemic atrophy and Motor Neuron Disease
G21.4Vascular parkinsonismCan lead a claimBSpinal Muscular Atrophy, Systemic atrophy and Motor Neuron Disease
G21.8Other secondary parkinsonismCan lead a claimBSpinal Muscular Atrophy, Systemic atrophy and Motor Neuron Disease
G21.9Secondary parkinsonism, unspecifiedCan lead a claimBSpinal Muscular Atrophy, Systemic atrophy and Motor Neuron Disease

Sources: CMS HH PPS Grouper Software v07.2.26, effective 2026-10-01, for the clinical group, comorbidity subgroup, code-first conventions and primary-position flags; CDC NCHS ICD-10-CM FY2027 code descriptions for the family title and code wording. This is the crosswalk Medicare runs a claim through. Grouping also depends on admission source, timing, the OASIS functional items and the rest of the diagnosis list.

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