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  2. ICD-10-CM Codes List
  3. G00–G99
  4. G20-G26
  5. Secondary parkinsonism (G21)

Secondary parkinsonism (G21)

Secondary parkinsonism (ICD-10 code G21) covers a group of conditions where parkinsonian symptoms result from external causes such as drugs, toxins, infections, or brain injury rather than primary Parkinson’s disease.

This ICD-10 section includes specific codes for varied causes: G21.0 for malignant neuroleptic syndrome (also known as neuroleptic malignant syndrome), and G21.11 for neuroleptic-induced parkinsonism, which reflect drug-induced cases, particularly from neuroleptic or dopamine-blocking medications. Other codes like G21.19 cover parkinsonism caused by various drugs or toxins including manganese or methanol. Exposure to environmental toxins or poisons such as pesticides, carbon monoxide, or cyanide is coded under G21.2. Post-infectious causes like postencephalitic parkinsonism (G21.3), vascular parkinsonism due to blood vessel issues (G21.4), and other secondary forms from infections, hereditary disorders, or brain injuries are classified under G21.8. When the cause is unspecified, G21.9 is used. Understanding these distinctions helps medical coders select the precise ICD-10 code for documenting secondary parkinsonism accurately.

Instructional Notations

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.

  • Huntington's disease G10
  • neurocognitive disorder with Lewy bodies G31.83
  • Shy-Drager syndrome G90.3
  • syphilitic Parkinsonism A52.19

Clinical Terms

The following clinical terms provide additional context, helping users better understand the clinical background and common associations for each diagnosis listed in this section. Including related terms alongside ICD-10-CM codes supports coders, billers, and healthcare professionals in improving accuracy, enhancing documentation, and facilitating research or patient education.

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)