Horner Syndrome
- Miosis, ipsilateral ptosis, and sometimes ipsilateral reduced facial sweating (“anhidrosis”) caused by a lesion in the oculosympathetic pathway
- Lesion causing Horner syndrome may lie in the central, pre-ganglionic, or post-ganglionic segment of the oculosympathetic pathway
- Common causes of a central lesion (hypothalamus to high thoracic spinal cord): dorsolateral medullary infarction (Wallenberg syndrome), hypothalamic lesion
- Common causes of a pre-ganglionic lesion (thoracic spinal cord to superior cervical ganglion): paraspinal or chest tumors
- Common causes of a post-ganglionic lesion (superior cervical ganglion to eye): internal jugular vein cannulation, cervical carotid dissection, thyroid or other neck tumor, ear infection, cavernous sinus lesion, cluster headache
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Core clinical features
- Anisocoria is no greater than 2.5mm in dim light
- Both pupils constrict normally to bright light
- Ptosis on the side of the smaller pupil
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Trap: Horner syndrome can occur without ptosis—and rarely without anisocoria!
- Affected pupil dilates less promptly than the unaffected pupil when the room light is suddenly dimmed (“dilation lag”)
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Trap: “dilation lag” is extremely difficult to observe without pupillometry
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Possible accompanying clinical features
- Ipsilateral lower lid elevation (“upside down ptosis”)
- Ipsilateral conjunctival hyperemia
- Ipsilateral facial anhidrosis
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Trap: facial anhidrosis occurs only in central or pre-ganglionic lesions—and then is rarely observed without special tests!
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Possible imaging features
- Cervical carotid dissection
- Neck or thoracic mass
- Dorsolateral medullary infarction
- Hypothalamic lesion
- Physiologic anisocoria
- Episodic mydriasis
- Traumatic, inflammatory, dysplastic iridoplegia
- Exposure to instilled or aerosolized adrenergic or anticholinergic agents (“pharmacologic mydriasis”)
- Ptosis from trauma, senescence, or myasthenia gravis
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Confirm the diagnosis of Horner syndrome with topical pharmacologic testing
- Instill apraclonidine 0.5% in both eyes; wait 30 minutes and note whether the affected pupil becomes larger than the unaffected pupil (“reversal of anisocoria”), confirming a diagnosis of Horner syndrome
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Trap: topical apraclonidine 0.5% elevates the lid in normal subjects, so the diagnosis of Horner syndrome depends entirely on reversal of anisocoria
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Trap: apraclonidine-induced reversal of anisocoria may not occur if the Horner syndrome occurred less than 48 hours earlier
- In children aged under 24 months, instill cocaine 10% (to avoid life-threatening cardiopulmonary side effects of apraclonidine), wait 30 minutes to see if there is less than 1mm of residual anisocoria, confirming a diagnosis of Horner syndrome
- If non-ophthalmic features allow localization of the lesion, concentrate imaging appropriately
- For acute isolated Horner syndrome, perform CT/CTA or MRI/MRA designed to detect cervical carotid artery dissection
- For non-acute isolated Horner syndrome, perform CT/CTA or MRI/MRA between the upper thoracic region and the skull base designed to detect carotid artery dissection but also masses in the chest or neck
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Tip: lesions of the neck and carotid canal may cause an isolated Horner syndrome, but lesions in the cavernous sinus, diencephalon, and brainstem do not cause an isolated Horner syndrome--other neuro-ophthalmic or neurologic deficits will always be present!
- Horner syndrome often persists even if the underlying lesion goes away
- About 50% of isolated Horner syndrome cases are of undetermined origin
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Tip: topical apraclonidine 0.5% may be prescribed safely to relieve the ptosis of Horner syndrome as an alternative to lid-lifting surgery