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Horner syndrome is ptosis, miosis, and anhidrosis due to dysfunction of cervical sympathetic output.
Horner syndrome results when the cervical sympathetic pathway running from the hypothalamus to the eye is disrupted. The causative lesion may be primary (including congenital) or secondary to another disorder. Lesions are usually divided into
Peripheral lesions may be preganglionic or postganglionic in origin.
Instilling eyedrops can help confirm and characterize Horner syndrome. First, cocaine (4 to 5%) or apraclonidine (0.5%) drops are put in both eyes. The following results suggest Horner syndrome:
Cocaine: The pupil of the unaffected eye dilates, but the pupil of the affected eye does not, resulting in increased anisocoria.
Apraclonidine: The pupil of the unaffected eye dilates minimally, and the pupil of the affected eye dilates much more, resulting in decreased anisocoria. (However, results may be falsely normal if the causative lesion is acute.)
If results suggest Horner syndrome, hydroxyamphetamine (1%) can be put in both eyes 48 h later to locate the lesion, as follows:
Postganglionic lesion: The pupil of the affected eye does not dilate, but the pupil of the unaffected eye does, resulting in increased anisocoria.
Central or preganglionic lesion: The pupil of the affected eye dilates normally or more than it normally does, and the pupil of the unaffected eye dilates normally, resulting in decreased or unchanged anisocoria. (However, postganglionic lesions sometimes produce the same results.)
Patients with Horner syndrome require MRI or CT of the brain, spinal cord, chest, or neck, depending on clinical suspicion.
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