ICD-10 Code G90.2 – Horner’s syndrome (2026): Diagnosis, Symptoms & Billing Guide
2026 ICD-10-CM Diagnosis Code G90.2 – Horner’s syndrome
What it is
Horner’s syndrome is a disorder caused by disruption of the sympathetic nerve supply to the face and eye. It typically affects one side and may occur from a lesion anywhere along that nerve pathway.
Clinical signs
Common findings include ptosis, miosis, and facial anhidrosis on the affected side. Clinical features vary; refer to documentation for the underlying cause and laterality, if noted.
When to use this code
Use G90.2 when the record clearly documents Horner’s syndrome as the diagnosis or a confirmed clinical finding. You may also use it when the syndrome is being evaluated and the provider documents it explicitly, even if the cause is still under workup.
Code the condition only when the documentation supports true Horner’s syndrome, not just isolated eyelid droop or pupil asymmetry. Check documentation for any associated underlying disorder that may also need coding.
Do not use for
Do not use this code for nonspecific ptosis, anisocoria, or facial sweating changes without a documented diagnosis of Horner’s syndrome. Do not assign it if the record only suggests the condition; check documentation.
Coding tip
Look for provider wording that confirms the syndrome and any stated cause, because the underlying condition may require separate coding.