2026 ICD-10-CM Diagnosis Code G21.0Malignant neuroleptic syndrome
ICD-10-CM Codes›G00–G99›G20-G26›G21
- Billable — Valid for Submission
- Chronic Condition
G21.0 is a billable ICD-10-CM diagnosis code for malignant neuroleptic syndrome. It is valid on HIPAA claims for fiscal year 2026 (October 1, 2025 through September 30, 2026). Coders also document this condition as neuroleptic malignant syndrome. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Drug induced or toxic related condition and Other nervous system disorders (often hereditary or degenerative).
Code Identity
Code Classification
Approximate SynonymsGuidance
Alternate terms and clinical phrases that map to this code.
- Neuroleptic malignant syndrome
Tabular List NotesGuidance
Coding notes and annotation back-references applicable to this code.
Use Additional Code
Type 1 Excludes
- neuroleptic induced parkinsonism G21.11
The “use additional code” indicates that a secondary code could be used to further specify the patient’s condition. This note is not mandatory and is only used if enough information is available to assign an additional code.
A type 1 excludes note is a pure excludes note. It means "NOT CODED HERE!" An Excludes1 note indicates that the code excluded should never be used at the same time as the code above the Excludes1 note. An Excludes1 is used when two conditions cannot occur together, such as a congenital form versus an acquired form of the same condition.
Index to Diseases and InjuriesGuidance
Alphabetical index entries that point to this code.
- Syndrome - See Also: Disease;
- neuroleptic - G21.0
External Cause of Injuries IndexGuidance
References for this code in the External Cause of Injuries Index.
- Syndrome
- malignant
- neuroleptic
Clinical ClassificationClinical
AHRQ’s CCSR groups this code into broader clinical categories.
Clinical InformationClinical
Neuroleptic Malignant Syndrome
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)
Patient EducationClinical
Drug Reactions
Most of the time, medicines make our lives better. They reduce aches and pains, fight infections, and control problems such as high blood pressure or diabetes. But medicines can also cause unwanted reactions, such as drug interactions, side effects, and allergies.
The full article covers:
- What is a drug interaction?
- What are side effects?
- What are drug allergies?
- How can I stay safe when taking medicines?
Read the full article at MedlinePlus
Courtesy of MedlinePlus, a service of the U.S. National Library of Medicine.
Convert G21.0 to ICD-9-CMHistory
The closest ICD-9-CM equivalents under the General Equivalence Mappings.
Code HistoryHistory
Questions About G21.0Overview
Is G21.0 (Secondary parkinsonism) a billable code?
Yes. This is a billable ICD-10-CM code, specific enough to report malignant neuroleptic syndrome on HIPAA-covered claims from October 1, 2025 through September 30, 2026.
What is the ICD-9 equivalent of G21.0?
Under the General Equivalence Mappings, malignant neuroleptic syndrome converts to ICD-9-CM 333.92 (neuroleptic malgnt synd). The mapping is a direct match.
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.
