Secondary parkinsonism (G21) ICD-10-CM
The G21 code range covers secondary parkinsonism with 10 ICD-10-CM diagnosis codes. 8 of them are billable and valid for claim submission in fiscal year 2027, and the category headers group them but cannot themselves be billed.
Type 1 Excludes
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.
Codes in the G21 Range 10 codes · 8 billable
- G21 Secondary parkinsonismNon-billable
- G21.0 Malignant neuroleptic syndrome
- G21.1 Other drug-induced secondary parkinsonismNon-billable
- 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
Clinical Terms in This Code Range
Definitions from the National Library of Medicine for conditions coded in the G21 range.
Neuroleptic Malignant Syndrome
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.
Parkinson Disease, Postencephalitic
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)
Parkinson Disease, Secondary
Conditions which feature clinical manifestations resembling primary Parkinson disease that are caused by a known or suspected condition. Examples include parkinsonism caused by vascular injury, drugs, trauma, toxin exposure, neoplasms, infections and degenerative or hereditary conditions. Clinical features may include bradykinesia, rigidity, parkinsonian gait, and masked facies. In general, tremor is less prominent in secondary parkinsonism than in the primary form. (From Joynt, Clinical Neurology, 1998, Ch38, pp39-42)
About the G21 Code Range
Secondary parkinsonism resembles primary Parkinson disease but stems from a known or suspected condition. This category sits among nervous system movement disorders.
G21 separates drug-induced cases from those linked to other external agents, encephalitis or vascular injury. G21.1 divides drug-induced parkinsonism into neuroleptic-induced G21.11 and other drug-induced G21.19 forms. Separate subdivisions name malignant neuroleptic syndrome G21.0, other external agents G21.2, parkinsonism following encephalitis G21.3, and vascular parkinsonism G21.4. The remaining subdivisions distinguish other secondary parkinsonism G21.8 from unspecified secondary parkinsonism G21.9.
Questions About This Page
How many billable codes are in the G21 range?
Of the 10 codes in this range, 8 are billable and valid for claim submission from October 1, 2026 through September 30, 2027. Category header codes group them but cannot be reported on claims.
What does the G21 range classify?
The range classifies secondary parkinsonism. Each code links to its own reference page with billing status, MS-DRG grouping, coding notes, and clinical information.
Related References
Source: CMS FY 2027 ICD-10-CM Tabular List and order file, effective October 1, 2026 through September 30, 2027.
