Alphabetic Index FY2027

G21.0

Malignant neuroleptic syndrome

FY2027Chapter 6: Diseases of the nervous system/G20–G26 Extrapyramidal and movement disorders

BillableComplete code, valid to report
Care settingsHome Health Primary · Neuro RehabilitationHospital MCC

G21.0 (also written G210) is a billable ICD-10-CM diagnosis code for malignant neuroleptic syndrome. It is part of the FY2027 code set, effective October 1, 2026. It is one of the 8 codes in category G21 (Secondary parkinsonism). The Alphabetic Index lists it under 1 entry. Its coding notes include a Use additional code instruction, 5 Excludes1 entries and 8 Excludes2 entries.

Use additional code

Add the listed code as a secondary code, if known.

This code

Excludes1

Not coded here. The listed conditions generally should not be reported together.

This code
  • neuroleptic induced parkinsonism (G21.11)
Inherited from G21 Secondary parkinsonism
  • Huntington's disease (G10)
  • neurocognitive disorder with Lewy bodies (G31.83)
  • Shy-Drager syndrome (G90.3)
  • syphilitic Parkinsonism (A52.19)

Excludes2

Not included here. Both codes may be reported if the patient has both conditions.

Also from chapter/block level (8 notes)
Inherited from Chapter 6 Diseases of the nervous system
  • 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)

Care settings

How CMS programs treat this code. These are CMS claim edits and list entries, not coverage or eligibility rules.

Home Health Primary

Accepted as the primary (principal) diagnosis on a home health claim. The Home Health Grouper assigns it to the Neuro Rehabilitation clinical group.

Source: CMS Home Health Grouper Software v07.2.26, effective October 1, 2026

Hospital MCC

Counts as a major complication or comorbidity (MCC) when reported as a secondary diagnosis on an inpatient claim. It does not count when the principal diagnosis is one of the 59 codes in its exclusion list. Some MS-DRGs also ignore a CC or MCC that defines the DRG.

Source: CMS MS-DRG Definitions Manual v44, effective October 1, 2026, Appendix C

Alphabetic Index terms

Terms the official Alphabetic Index lists for this code. 1 entry