ICD-10 Code G04.0 – Acute disseminated encephalitis and encephalomyelitis (ADEM) (2026): Diagnosis, Symptoms & Billing Guide
2026 ICD-10-CM Diagnosis Code G04.0 – Acute disseminated encephalitis and encephalomyelitis (ADEM)
What it is
G04.0 identifies acute disseminated encephalitis and encephalomyelitis, also called ADEM. It is an inflammatory disorder of the brain and spinal cord, usually described as a sudden, widespread demyelinating illness.
Clinical signs
Typical findings include acute neurologic deficits such as altered mental status, weakness, sensory changes, ataxia, or visual symptoms. Clinical features vary; refer to documentation, especially when notes describe postinfectious or post-vaccination onset.
When to use this code
Use G04.0 when the provider documents ADEM or acute disseminated encephalitis/encephalomyelitis as the confirmed diagnosis. Apply it for inpatient or outpatient encounters where the record supports an acute demyelinating inflammatory CNS disorder. Check documentation if the note only says “encephalitis” without specifying ADEM.
Do not use for
Do not use this code for unspecified encephalitis, meningitis, or multiple sclerosis. If the chart does not clearly identify ADEM, code the documented condition instead and verify the diagnosis.
Coding tip
Code G04.0 only when ADEM is explicitly documented; otherwise, query the provider for clarification.