2021 ICD-10-CM Diagnosis Code G21.3

Postencephalitic parkinsonism

    2016 2017 2018 2019 2020 2021 Billable/Specific Code
  • G21.3 is a billable/specific ICD-10-CM code that can be used to indicate a diagnosis for reimbursement purposes.
  • The 2021 edition of ICD-10-CM G21.3 became effective on October 1, 2020.
  • This is the American ICD-10-CM version of G21.3 - other international versions of ICD-10 G21.3 may differ.
The following code(s) above G21.3 contain annotation back-references
Annotation Back-References
In this context, annotation back-references refer to codes that contain:
  • Applicable To annotations, or
  • Code Also annotations, or
  • Code First annotations, or
  • Excludes1 annotations, or
  • Excludes2 annotations, or
  • Includes annotations, or
  • Note annotations, or
  • Use Additional annotations
that may be applicable to G21.3:
  • G00-G99
    2021 ICD-10-CM Range G00-G99

    Diseases of the nervous system

    Type 2 Excludes
    • 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)
    Diseases of the nervous system
  • G21
    ICD-10-CM Diagnosis Code G21

    Secondary parkinsonism

      2016 2017 2018 2019 2020 2021 Non-Billable/Non-Specific Code
    Type 1 Excludes
    • dementia with Parkinsonism (G31.83)
    • Huntington's disease (G10)
    • Shy-Drager syndrome (G90.3)
    • syphilitic Parkinsonism (A52.19)
    Secondary parkinsonism
Approximate Synonyms
  • Parkinsonism, postencephalitic
Clinical Information
  • Parkinsonism following encephalitis, historically seen as a sequella of encephalitis lethargica (von economo encephalitis). The early age of onset, the rapid progression of symptoms followed by stabilization, and the presence of a variety of other neurological disorders (e.g., sociopathic behavior; tics; muscle spasms; oculogyric crises; hyperphagia; and bizarre movements) distinguish this condition from primary parkinson disease. Pathologic features include neuronal loss and gliosis concentrated in the mesencephalon; subthalamus; and hypothalamus. (from Adams et al., Principles of Neurology, 6th ed, p754)
ICD-10-CM G21.3 is grouped within Diagnostic Related Group(s) (MS-DRG v38.0):
  • 056 Degenerative nervous system disorders with mcc
  • 057 Degenerative nervous system disorders without mcc

Convert G21.3 to ICD-9-CM

Code History
  • 2016 (effective 10/1/2015): New code (first year of non-draft ICD-10-CM)
  • 2017 (effective 10/1/2016): No change
  • 2018 (effective 10/1/2017): No change
  • 2019 (effective 10/1/2018): No change
  • 2020 (effective 10/1/2019): No change
  • 2021 (effective 10/1/2020): No change

Diagnosis Index entries containing back-references to G21.3:
  • Parkinsonism (idiopathic) (primary) G20
    ICD-10-CM Diagnosis Code G20

    Parkinson's disease

      2016 2017 2018 2019 2020 2021 Billable/Specific Code
    Applicable To
    • Hemiparkinsonism
    • Idiopathic Parkinsonism or Parkinson's disease
    • Paralysis agitans
    • Parkinsonism or Parkinson's disease NOS
    • Primary Parkinsonism or Parkinson's disease
    Type 1 Excludes
    • dementia with Parkinsonism (G31.83)
    Use Additional
    • code to identify:
    • dementia with behavioral disturbance (F02.81)
    • dementia without behavioral disturbance (F02.80)
    • secondary G21.9
      ICD-10-CM Diagnosis Code G21.9

      Secondary parkinsonism, unspecified

        2016 2017 2018 2019 2020 2021 Billable/Specific Code
    • postencephalitic G21.3

ICD-10-CM Codes Adjacent To G21.3
G13.2 Systemic atrophy primarily affecting the central nervous system in myxedema
G13.8 Systemic atrophy primarily affecting central nervous system in other diseases classified elsewhere
G14 Postpolio syndrome
G20 Parkinson's disease
G21 Secondary parkinsonism
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
G21.4 Vascular parkinsonism
G21.8 Other secondary parkinsonism
G21.9 Secondary parkinsonism, unspecified
G23 Other degenerative diseases of basal ganglia
G23.0 Hallervorden-Spatz disease
G23.1 Progressive supranuclear ophthalmoplegia [Steele-Richardson-Olszewski]
G23.2 Striatonigral degeneration
G23.8 Other specified degenerative diseases of basal ganglia
G23.9 Degenerative disease of basal ganglia, unspecified
G24 Dystonia

Reimbursement claims with a date of service on or after October 1, 2015 require the use of ICD-10-CM codes.