ICD-10 Code G04.90 – Encephalitis and encephalomyelitis, unspecified (2026): Diagnosis, Symptoms & Billing Guide
2026 ICD-10-CM Diagnosis Code G04.90 – Encephalitis and encephalomyelitis, unspecified
What it is
G04.90 identifies inflammation of the brain, or the brain and spinal cord, when the provider does not specify the cause or exact type. Use this code when documentation supports encephalitis or encephalomyelitis but details are limited.
Clinical signs
Clinical features vary; refer to documentation. Common findings may include altered mental status, headache, fever, seizures, focal neurologic deficits, or signs of central nervous system inflammation.
When to use this code
Use G04.90 when the record states encephalitis or encephalomyelitis without a more specific diagnosis. It also fits cases where the provider documents inflammatory disease of the brain or brain and spinal cord, but the cause remains unspecified. If a more specific infectious, autoimmune, or postinfectious code is documented, code that instead.
Do not use for
Do not use this code for meningitis, encephalopathy, or demyelinating disease unless the provider clearly documents encephalitis or encephalomyelitis. If documentation names a specific organism or condition, check for a more precise code.
Coding tip
Query the provider when the note says “encephalitis” but does not clarify whether it is infectious, autoimmune, or another specific type.