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Horner’s Syndrome in a 17 Year Old

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Title: Horner’s Syndrome in a 17 year old

Author: Emily Ross, 4th Year Medical Student at Indiana University-Purdue University Indianapolis

Date: 9/21/2017

Keywords/Main Subjects: Horner’s syndrome, anisocoria, ptosis

CORE Category:

Neuro-Ophthalmology > Pupillary Abnormalities > Anisocoria

Diagnosis: Horner’s Syndrome

Description of Case:

The patient is a 17-year-old girl who presented with ptosis on the right and anisocoria that began four months prior to presentation at clinic. She denies any cough, chest pain, neck pain, eye pain, neck manipulation, trauma, or preceding illnesses. She has no other significant findings on exam and no significant medical history. She does not use any eye drops. Differential diagnosis: Horner’s Syndrome, physiologic anisocoria, Adie tonic pupil, or topical/systemic medications. The patient was found to have Horner’s Syndrome.

Horner’s Syndrome:

Horner’s syndrome can result from a lesion anywhere along the three neuron oculosympathetic pathway.  It can produce three main deficits: ipsilateral ptosis (eyelid drooping) because of loss of innervation to Muller’s muscle, ipsilateral miosis (pupillary constriction) because of unopposed parasympathetic drive to the pupil, and ipsilateral anhydrosis (lack of sweating) on the face that may be best appreciated by the patient as contralateral hemifacial redness during exertion. This hemifacial redness is called the harlequin sign.

When evaluating a patient with anisocoria, first check that both pupils react appropriately to light, then determine if the difference in pupil size is greater in dim light or bright light. Horner’s Syndrome will have a greater difference seen between the two pupils in dim light. Dilation lag will also be present in Horner’s Syndrome and can help differentiate it from physiologic anisocoria. When the normal pupil dilates, there is both a parasympathetic signal allowing relaxation of the sphincter and a sympathetic signal contracting the pupillary dilator muscle. In Horner’s syndrome, the sympathetic signal is absent so the pupil only dilates by parasympathetic sphincter relaxation which is not as brisk resulting in a slower dilation response to dim light.

Figure 1: Dilation lag: After five seconds in dim light, the left (unaffected) pupil has dilated to 7mm, while the right (affected) pupil is only dilated to 5mm. After 15 seconds, the left pupil is dilated to 7.5mm and the right is dilated to almost 7mm.

Confirming the diagnosis of Horner’s Syndrome can be accomplished pharmacologically using either cocaine or aproclonidine eye drops. Cocaine is a norepinephrine reuptake inhibitor. When instilled in a patient with Horner’s Syndrome, the unaffected pupil will dilate significantly while the affected pupil will have a minimal or no response. The sympathetic innervation to the affected pupil is absent so the cocaine will have no (or very little) norepinephrine present in the synapse to prevent reuptake of resulting in little or no dilation of the pupil. Additionally, after a positive cocaine test, one can apply topical phenylephrine to the miotic pupil which directly stimulates sympathetic receptors resulting in dilation of the affected pupil. Aproclonidine is a strong alpha-2 adrenergic agonist and a weak alpha-1 adrenergic agonist. In the unaffected pupil, the alpha-2 stimulation results in pupillary constriction but in the affected pupil, the alpha-1 receptors become hypersensitive about one week after the sympathetic denervation and will cause pupillary dilation reversing the anisocoria as well as improvement of the ptosis.

Figure 2: Cocaine eye drop test: Upon presenting to clinic, the patient shows anisocoria with a smaller left pupil and ptosis on the left. Thirty minutes after application of 4% cocaine eye drops in room light, the right pupil has dilated significantly while the left pupil remains unaffected confirming the diagnosis of Horner’s Syndrome.

Localizing the lesion to either a first order or second order neuron lesion (preganglionic) versus a third order neuron (postganglionic) lesion can be accomplished pharmacologically by using hydroxyamphetamine eye drops though these drops are not routinely available even at large institutions. If the postganglionic neuron is functioning, the hydroxyamphetamine will cause release of norepinephrine from the neuron resulting in pupil dilation and narrowing the differential to a lesion in either the central or preganglionic neurons. If there is no dilation, then the lesion has been localized to the postganglionic neuron. If a cocaine test is performed, one must wait at least 24 hours before performing the hydroxyamphetamine test as the cocaine can interfere with this localizing test. Additionally, history and exam findings may also assist the clinician in localizing the lesion.

Understanding the anatomy of the oculosympathetic pathway is crucial. First order or central neurons run from the hypothalamus through the brainstem and spinal cord to the level of C8/T1. Second order or preganglionic neurons exit the brainstem and ascend to the superior cervical ganglion located near the carotid artery bifurcation. On this route, second order neurons pass near the subclavian artery and lung apex. Third order or postganglionic neurons begin at the superior cervical ganglion and run with the internal carotid artery.

Imaging of the head, neck, and chest may be required to establish an underlying cause for the Horner’s syndrome with either MRI, CT, angiography, or ultrasound.  Wallenberg Syndrome, carotid artery dissections, Pancoast or apical lung tumors, basal skull tumors, dislocation of cervical vertebrae, aortic dissection or aneurysm, and iatrogenic causes are a few potential etiologies of a Horner’s Syndrome to investigate.


  1. Ophthalmology AA of. 2017-2018 Basic and Clinical Science Course Neuro-Ophthalmology. S.I.: American Academy of Ophthalmology; 2017.
  2. Kanagalingan S, Miller NR. Horner syndrome: clinical perspectives. Eye and Brain. April 2015; (10)7:35-46. doi: 10.2147/EB.S63633.
  3. Davagnanam I, Fraser CL, Miszkiel K, Daniel CS, Plant GT. Adult Horner’s syndrome: a combined clinical, pharmacological, and imaging algorithm. Eye. March 2013; 27(3):291-8. doi: 10.1038/eye.2012.281.
  4. Kedar S, Biousse V, Newman N. Horner Syndrome. Post TW, ed. UpToDate. Waltham, MA: UpToDate Inc. (Accessed on September 23, 2017.)

Identifier: Moran_CORE_24942

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