G21.3 Postencephalitic parkinsonism

Billable ICD-10-CM code, FY2026. Acts as a Complication or Comorbidity (CC) as a secondary diagnosis.

Applies from G21 Secondary parkinsonism

Excludes1 (never code together)

• Huntington's disease (G10)
• neurocognitive disorder with Lewy bodies (G31.83)
• Shy-Drager syndrome (G90.3)
• syphilitic Parkinsonism (A52.19)

Risk adjustment (HCC)

• CMS-HCC V28: HCC 199 — Parkinson and Other Degenerative Disease of Basal Ganglia
• CMS-HCC V22: HCC 78 — Parkinson's and Huntington's Diseases
• RxHCC V08: HCC 161 — Parkinson Disease
• ESRD V24: HCC 78

MS-DRG index

Defines the logic of DRG(s) 056-057 in MDC 01.

Approximate ICD-9-CM (GEMs)

• 332.1 Secondary parkinsonism (approximate)

Code annotations containing back-references to G21.3

Back-references to G21

• Type 2 Excludes: F98.4 Stereotyped movement disorders ("movement disorders of organic origin (G20-G25)")
• Type 1 Excludes: G20.C Parkinsonism, unspecified ("secondary parkinsonism (G21.-)")
• Type 1 Excludes: R25 Abnormal involuntary movements ("specific movement disorders (G20-G26)")

Diagnosis Index entries for G21.3

• Parkinsonism (idiopathic) (primary) › postencephalitic
• Parkinsonism (idiopathic) (primary) › secondary › due to › encephalitis

Nearby codes

• G21.0 Malignant neuroleptic syndrome
• G21.1 Other drug-induced secondary parkinsonism
• G21.11 Neuroleptic induced parkinsonism
• G21.19 Other drug induced secondary parkinsonism
• G21.2 Secondary parkinsonism due to other external agents
• G21.3 Postencephalitic parkinsonism (this code)
• G21.4 Vascular parkinsonism
• G21.8 Other secondary parkinsonism
• G21.9 Secondary parkinsonism, unspecified