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Horner Syndrome

URGENT — Signs

Symptoms

ptosis and anisocoria (often asymptomatic)

anhidrosis (lack of sweating) on affected side

acute painful horner: neck or face pain suggests carotid dissection

Clinical Findings

Pupil

  • anisocoria greater in dim illumination (dilation lag)
  • affected pupil is smaller (miosis) and dilates slower than the normal eye
  • light and near reactions are intact

Eyelid

  • mild ptosis (~2 mm) from müller muscle weakness
  • "upside-down ptosis" (elevation of the lower lid)

Other signs

  • iris heterochromia (lighter iris on affected side) if congenital
  • conjunctival hyperemia and slightly lower iop on affected side
  • transiently increased accommodative amplitude

Etiology

First-order (central)

  • stroke (e.g., wallenberg syndrome), tumor, or multiple sclerosis

Second-order (preganglionic)

  • pancoast tumor (lung apex), thyroid adenoma, or aortic aneurysm
  • pediatric: neuroblastoma or birth trauma

Third-order (postganglionic)

  • internal carotid artery dissection
  • cavernous sinus pathology or tollosa-hunt syndrome
  • cluster headache or migrainous syndromes
  • neck trauma or otitis media

Red Flags

acute painful horner (neck/face pain): emergent carotid artery dissection risk

horner with arm pain/wasting: suggests pancoast tumor

pediatric horner without surgery history: requires neuroblastoma workup

horner with cranial nerve palsies: suggests brainstem or cavernous sinus lesion

Investigations

Pharmacologic testing

  • apraclonidine 0.5%: reversal of anisocoria confirms horner (affected pupil dilates)
  • hydroxyamphetamine: failure to dilate suggests third-order (postganglionic) lesion
  • cocaine 10%: failure of horner pupil to dilate confirms the diagnosis

Imaging

  • cta or mra of head and neck: mandatory for acute painful horner (dissection)
  • mri brain/neck/chest: to evaluate the full oculosympathetic pathway

Pediatric specialty

  • urinary catecholamines (vma/hva) and chest/abdominal imaging for neuroblastoma

Treatment

Primary

  • directed at the underlying systemic cause (e.g., tumor, stroke, or dissection)

Vascular

  • anticoagulation or antiplatelet therapy for carotid dissection

Surgical

  • müller muscle resection for stable, symptomatic ptosis after clear diagnosis

Clinical Pearl

Horner localization matters: Central (first-order — brain/brainstem): MRI brain. Preganglionic (second-order — from C8-T2 via lung apex): MRI/CT chest, look for Pancoast tumor. Postganglionic (third-order — carotid/cavernous): MRA carotid, look for carotid dissection. In acute painful Horner: carotid dissection until proven otherwise.

Differential Diagnosis

  • physiologic anisocoria (equal in light and dark)
  • pharmacologic miosis
  • adie tonic pupil (anisocoria greater in light)
  • third nerve palsy (ptosis with a large pupil)
  • traumatic miosis

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