ICD-10 Code B00.4 – Herpesviral encephalitis (2026): Diagnosis, Symptoms & Billing Guide
2026 ICD-10-CM Diagnosis Code B00.4 – Herpesviral encephalitis
What it is
B00.4 identifies encephalitis caused by herpes simplex virus. Use it when the record documents herpesviral infection of the brain, not just a skin or mucosal herpes outbreak.
Clinical signs
Typical findings include acute fever, headache, altered mental status, seizures, or focal neurologic deficits. Clinical features vary; refer to documentation for the confirmed viral cause and neurologic involvement.
When to use this code
Use B00.4 when the provider diagnoses herpesviral encephalitis or herpes simplex encephalitis. It fits inpatient or outpatient documentation that clearly links encephalitis to herpes infection. If the note only says “herpes” without brain involvement, do not assign this code.
Do not use for
Do not use B00.4 for uncomplicated oral, genital, or cutaneous herpes. Also avoid it when encephalitis is documented without a herpesviral cause; check documentation.
Coding tip
Confirm both encephalitis and herpesviral etiology in the provider’s wording before coding B00.4.