ICD-10 Code G04.01 – Postinfectious acute disseminated encephalitis and encephalomyelitis (postinfectious ADEM) (2026): Diagnosis, Symptoms & Billing Guide
2026 ICD-10-CM Diagnosis Code G04.01 – Postinfectious acute disseminated encephalitis and encephalomyelitis (postinfectious ADEM)
What it is
G04.01 identifies postinfectious acute disseminated encephalitis and encephalomyelitis, an inflammatory demyelinating disorder that follows an infection. Use it when the record specifically links the neurologic illness to a recent infection.
Clinical signs
Typical documentation may include acute or subacute encephalopathy, multifocal neurologic deficits, and evidence of demyelination after infection. Clinical features vary; refer to documentation.
When to use this code
Use this code when the provider diagnoses postinfectious ADEM or documents acute disseminated encephalomyelitis after a recent infectious illness. It may appear in neurology, inpatient, or discharge documentation when the causal relationship is stated clearly. If the note only says “encephalitis” or “demyelinating disease,” check documentation.
Do not use for
Do not use G04.01 for encephalopathy without demyelinating features or for infectious encephalitis without a postinfectious link. Check documentation if the condition is described as autoimmune, unspecified, or another demyelinating disorder.
Coding tip
Look for explicit wording such as “postinfectious ADEM” or “acute disseminated encephalomyelitis” before assigning G04.01.