ICD-10 Code G04.02 – Postimmunization acute disseminated encephalitis, myelitis and encephalomyelitis (2026): Diagnosis, Symptoms & Billing Guide
2026 ICD-10-CM Diagnosis Code G04.02 – Postimmunization acute disseminated encephalitis, myelitis and encephalomyelitis
What it is
This code identifies an acute inflammatory disorder of the brain and spinal cord that occurs after immunization. Use it when documentation links the demyelinating or encephalitic process to a recent vaccine.
Clinical signs
Clinical features vary; refer to documentation. Findings may include acute neurologic deficits, altered mental status, weakness, sensory changes, or signs of encephalitis, myelitis, or combined encephalomyelitis.
When to use this code
Use G04.02 when the provider documents postimmunization acute disseminated encephalitis, myelitis, or encephalomyelitis, or clearly states a vaccine-related inflammatory demyelinating event. It may also apply when the chart specifies a temporal relationship to immunization and the diagnosis is confirmed. If the record only suggests a possible association, check documentation.
Do not use for
Do not use this code for routine vaccine reactions, nonspecific neurologic symptoms, or encephalitis without a documented postimmunization cause. Do not assign it if the condition is postinfectious, autoimmune, or otherwise unrelated to immunization.
Coding tip
Verify that the provider explicitly connects the neurologic diagnosis to immunization before assigning G04.02.