ICD-10 Code B01.1 – Varicella encephalitis, myelitis and encephalomyelitis (2026): Diagnosis, Symptoms & Billing Guide
2026 ICD-10-CM Diagnosis Code B01.1 – Varicella encephalitis, myelitis and encephalomyelitis
What it is
B01.1 identifies neurologic inflammation caused by varicella infection, including encephalitis, myelitis, or combined encephalomyelitis. Use it when documentation links these nervous system complications to chickenpox.
Clinical signs
Clinical features vary; refer to documentation. Commonly recorded findings include altered mental status, seizures, focal neurologic deficits, or spinal cord symptoms such as weakness and sensory changes.
When to use this code
Use this code when the provider documents varicella with encephalitis, myelitis, or encephalomyelitis. It also fits cases where the neurologic complication is clearly attributed to active varicella infection. If the record only says “chickenpox” without neurologic involvement, do not assign B01.1.
Do not use for
Do not use this code for uncomplicated varicella or for neurologic disease without documented varicella causation. Check documentation if the record describes encephalitis or myelitis from another infection.
Coding tip
Confirm both the varicella diagnosis and the specific neurologic complication in the provider note before coding B01.1.