2021 ICD-10-CM Diagnosis Code G21.0

Malignant neuroleptic syndrome

    2016 2017 2018 2019 2020 2021 Billable/Specific Code
  • G21.0 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 G21.0 became effective on October 1, 2020.
  • This is the American ICD-10-CM version of G21.0 - other international versions of ICD-10 G21.0 may differ.
Use Additional
Use Additional Help
Certain conditions have both an underlying etiology and multiple body system manifestations due to the underlying etiology. For such conditions the ICD-10-CM has a coding convention that requires the underlying condition be sequenced first followed by the manifestation. Wherever such a combination exists there is a "use additional code" note at the etiology code, and a "code first" note at the manifestation code. These instructional notes indicate the proper sequencing order of the codes, etiology followed by manifestation. In most cases the manifestation codes will have in the code title, "in diseases classified elsewhere." Codes with this title are a component of the etiology/manifestation convention. The code title indicates that it is a manifestation code. "In diseases classified elsewhere" codes are never permitted to be used as first listed or principle diagnosis codes. They must be used in conjunction with an underlying condition code and they must be listed following the underlying condition.
  • code for adverse effect, if applicable, to identify drug (
    ICD-10-CM Diagnosis Code T43.3X5

    Adverse effect of phenothiazine antipsychotics and neuroleptics

      2016 2017 2018 2019 2020 2021 Non-Billable/Non-Specific Code
    T43.3X5
    ,
    ICD-10-CM Diagnosis Code T43.4X5

    Adverse effect of butyrophenone and thiothixene neuroleptics

      2016 2017 2018 2019 2020 2021 Non-Billable/Non-Specific Code
    T43.4X5
    ,
    ICD-10-CM Diagnosis Code T43.505

    Adverse effect of unspecified antipsychotics and neuroleptics

      2016 2017 2018 2019 2020 2021 Non-Billable/Non-Specific Code
    T43.505
    ,
    ICD-10-CM Diagnosis Code T43.595

    Adverse effect of other antipsychotics and neuroleptics

      2016 2017 2018 2019 2020 2021 Non-Billable/Non-Specific Code
    T43.595
    )
Type 1 Excludes
Type 1 Excludes Help
A type 1 excludes note is a pure excludes. It means "not coded here". A type 1 excludes note indicates that the code excluded should never be used at the same time as G21.0. A type 1 excludes note is for used for when two conditions cannot occur together, such as a congenital form versus an acquired form of the same condition.
  • neuroleptic induced parkinsonism (
    ICD-10-CM Diagnosis Code G21.11

    Neuroleptic induced parkinsonism

      2016 2017 2018 2019 2020 2021 Billable/Specific Code
    Type 1 Excludes
    • malignant neuroleptic syndrome (G21.0)
    Use Additional
    G21.11
    )
The following code(s) above G21.0 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 G21.0:
  • 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
  • Neuroleptic malignant syndrome
Clinical Information
  • A life-threatening condition that may be caused by certain drugs used to treat mental illness, nausea, or vomiting. Symptoms include high fever, sweating, unstable blood pressure, confusion, and stiffness.
  • A potentially fatal syndrome associated primarily with the use of neuroleptic agents (see antipsychotic agents) which are in turn associated with dopaminergic receptor blockade (see receptors, dopamine) in the basal ganglia and hypothalamus, and sympathetic dysregulation. Clinical features include diffuse muscle rigidity; tremor; high fever; diaphoresis; labile blood pressure; cognitive dysfunction; and autonomic disturbances. Serum cpk level elevation and a leukocytosis may also be present. (from Adams et al., Principles of Neurology, 6th ed, p1199; psychiatr serv 1998 sep;49(9):1163-72)
  • A rare, life-threatening disorder that is caused by neuroleptic medications. It is characterized by fever, muscular cramps and rigidity, autonomic nervous system dysfunction, and changes in the mental status that may lead to coma.
ICD-10-CM G21.0 is grouped within Diagnostic Related Group(s) (MS-DRG v38.0):
  • 091 Other disorders of nervous system with mcc
  • 092 Other disorders of nervous system with cc
  • 093 Other disorders of nervous system without cc/mcc

Convert G21.0 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
Code annotations containing back-references to G21.0:
  • Type 1 Excludes: G21.11
    ICD-10-CM Diagnosis Code G21.11

    Neuroleptic induced parkinsonism

      2016 2017 2018 2019 2020 2021 Billable/Specific Code
    Type 1 Excludes
    • malignant neuroleptic syndrome (G21.0)
    Use Additional

Diagnosis Index entries containing back-references to G21.0:

ICD-10-CM Codes Adjacent To G21.0
G12.8 Other spinal muscular atrophies and related syndromes
G12.9 Spinal muscular atrophy, unspecified
G13 Systemic atrophies primarily affecting central nervous system in diseases classified elsewhere
G13.0 Paraneoplastic neuromyopathy and neuropathy
G13.1 Other systemic atrophy primarily affecting central nervous system in neoplastic disease
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

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