ICD-10 Code G21.0 – Malignant Neuroleptic Syndrome (2026): Diagnosis, Symptoms & Billing Guide
2026 ICD-10-CM Diagnosis Code G21.0 – Malignant neuroleptic syndrome
What it is
G21.0 identifies malignant neuroleptic syndrome, a rare but serious reaction linked to dopamine-blocking medicines. Use it when documentation states this diagnosis or an equivalent term.
Clinical signs
Typical findings include severe muscle rigidity, altered mental status, autonomic instability, and fever. Clinical features vary; refer to documentation.
When to use this code
Use G21.0 when the provider documents malignant neuroleptic syndrome, neuroleptic malignant syndrome, or an equivalent diagnosis. It may apply during an inpatient complication or after exposure to antipsychotic or other dopamine-blocking medication. Check documentation if the record only describes adverse drug reaction without a confirmed syndrome.
Do not use for
Do not use this code for uncomplicated medication side effects, nonspecific fever, or isolated extrapyramidal symptoms. If the diagnosis is uncertain, code the documented signs and symptoms instead.
Coding tip
Confirm the exact provider diagnosis and document the medication exposure when available.