Horner Syndrome

Interruption of the oculosympathetic pathway (central first order neuron from hypothalamus to the ciliospinal centre, preganglionic second order neuron over the lung apex and around the subclavian artery, postganglionic third order neuron along the internal carotid artery to the eye).

• Classic triad: ptosis (mild, 1 to 2 mm), miosis, and anhidrosis, plus lower lid elevation ("upside down ptosis") and enophthalmos appearance.
• First order: brainstem stroke (lateral medullary syndrome), demyelination, syrinx, tumour. Second order: Pancoast tumour, thyroid mass, neck trauma, thoracic surgery, central line, aortic aneurysm, cervical rib. Third order: carotid artery dissection, cluster headache, cavernous sinus lesion, otitis media, skull base tumour.
• Congenital Horner: birth trauma, brachial plexus injury; heterochromia iridis (lighter iris) in the affected eye.

• Ptosis and miosis, with anisocoria greatest in dim light because the Horner pupil dilates slowly (dilation lag at 5 seconds, visible up to 15 to 20 seconds).
• Anhidrosis: face and neck (first and second order), forehead spared in third order (sudomotor fibres to the forehead travel on the external carotid).
• Painful Horner syndrome with neck or facial pain, with or without transient ischaemic attack or stroke: carotid dissection until proven otherwise.
• Associated signs: Pancoast (shoulder, arm pain, hand wasting), lateral medullary (vertigo, ataxia, contralateral loss of pain and temperature sensation), cluster headache, abducens palsy (cavernous sinus).

• Confirm the Horner pupil:
  • Apraclonidine 0.5 percent (1 percent in some regions), 1 drop in each eye, repeat after 30 to 60 minutes: reversal of anisocoria (the Horner pupil dilates, the normal pupil stays unchanged) confirms the diagnosis. Unreliable in the first week after onset and in infants.
  • Cocaine 4 or 10 percent, 2 drops in each eye, remeasure at 40 to 60 minutes: the Horner pupil fails to dilate (anisocoria of 0.8 mm or greater post-drop).
• Localise: hydroxyamphetamine 1 percent drops (wait 48 hours after cocaine or apraclonidine): a pupil that dilates indicates an intact third order neuron (central or preganglionic lesion); failure to dilate indicates a postganglionic lesion. Where unavailable, rely on associated signs and imaging.
• Imaging:
  • Acute painful Horner or neck pain, trauma: urgent CT or MR angiography of the head and neck, including aortic arch.
  • Isolated Horner of unknown cause: MRI brain with MRA, plus CT or MRI neck and chest to the lung apex, up to the T2 level. Chest X-ray as a first test if CT delayed.
  • Children: MRI brain, neck, chest and abdomen; urine catecholamine metabolites (VMA, HVA) and spot urine to exclude neuroblastoma.
• ESR and CRP in patients over 50 (giant cell arteritis can cause Horner).

• Treat the cause.
  • Carotid dissection: antithrombotic therapy, either aspirin 300 mg daily or heparin infusion (target aPTT 1.5 to 2 times control) then warfarin to INR 2 to 3 for 3 to 6 months; thrombolysis if within window and no contraindication.
  • Pancoast: multimodality therapy (chemoradiotherapy followed by surgery) as directed by oncology.
  • Cluster headache: high flow oxygen 100 percent 12 to 15 L/min for 15 minutes, sumatriptan 6 mg subcutaneously; verapamil 240 to 480 mg daily for prophylaxis.
  • Neuroblastoma: oncological referral.
• Ptosis: observation, then phenylephrine 2.5 percent drops or oxymetazoline 0.1 percent drops for cosmetic elevation; surgical correction with Müller muscle conjunctival resection or a small levator advancement after the cause is stable.
• Congenital Horner usually requires no treatment beyond amblyopia monitoring and ptosis correction if visually significant.