Horner syndrome
Horner syndrome is an oculosympathetic palsy causing the ipsilateral triad of miosis, partial ptosis, and anhidrosis from a lesion anywhere along the three-neuron sympathetic pathway to the eye and face. Diagnosis is clinical, confirmed with apraclonidine or cocaine eye drops; management targets the underlying cause, which ranges from benign to an emergent carotid dissection or Pancoast tumor.
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What this article covers
- Overview
Definition: Horner syndrome (oculosympathetic palsy) is the clinical triad of ipsilateral miosis, partial ptosis, and anhidrosis resulting from interruption of the sympathetic innervation to the eye…
- Epidemiology
Uncommon, underrecognized: Horner syndrome is relatively rare and often subtle, particularly partial or congenital forms, and can be missed unless anisocoria and ptosis are specifically compared side to side.
- Risk factors
Cervical or thoracic surgery: thyroidectomy, carotid endarterectomy, chest tube placement, and central line insertion near the neck can injure the sympathetic chain.
- Pathophysiology
Sympathetic outflow interruption: any lesion along the three-neuron oculosympathetic pathway disrupts noradrenergic innervation to the iris dilator muscle, Muller muscle (superior tarsal muscle), and facial sweat glands.
- Clinical features
Ipsilateral miosis: the affected pupil is smaller, with anisocoria most pronounced in dim light and a sluggish dilation response.
- Differential diagnosis
Oculomotor (cranial nerve III) palsy: a dilated, poorly reactive "blown" pupil with complete ptosis and impaired extraocular movements (down-and-out position), the opposite pupillary direction from Horner syndrome, with no anhidrosis.
- Diagnosis
Clinical diagnosis, confirmed pharmacologically: the triad of miosis, ptosis, and anhidrosis on careful side-to-side comparison establishes clinical suspicion; pharmacologic testing confirms the…
- Management
First, identify and treat the underlying cause; Horner syndrome itself has no direct treatment, and management is entirely determined by the causative lesion.
- Complications
Missed carotid dissection: the most serious consequence of a missed diagnosis, with risk of ischemic stroke from embolization or hemodynamic compromise if antithrombotic therapy is delayed.
- Prognosis
Horner syndrome itself does not affect vision and rarely resolves spontaneously in acquired cases, but it is not dangerous on its own; prognosis is governed entirely by the underlying etiology.
- Prevention
No direct primary prevention exists for Horner syndrome, since it is a sign of an underlying lesion rather than a preventable disease process in itself.
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