ICD-10 Code G21.3 – Postencephalitic parkinsonism (2026): Diagnosis, Symptoms & Billing Guide
2026 ICD-10-CM Diagnosis Code G21.3 – Postencephalitic parkinsonism
What it is
Use this code for parkinsonian syndrome that develops after encephalitis. It reflects a secondary cause of parkinsonism rather than idiopathic Parkinson disease.
Clinical signs
Typical findings include bradykinesia, rigidity, tremor, and gait or postural instability. Clinical features vary; refer to documentation for the encephalitis history and neurologic findings.
When to use this code
Assign G21.3 when the record clearly links parkinsonian symptoms to prior encephalitis. Use it for documented postinfectious or postencephalitic parkinsonism, including cases described as delayed neurologic sequelae. If the cause is not stated, check documentation before coding.
Do not use for
Do not use this code for idiopathic Parkinson disease or other secondary parkinsonism without an encephalitis cause. Check documentation if the chart only says “parkinsonism” or “movement disorder.”
Coding tip
Capture both the parkinsonism and the encephalitis history when the record supports the link.