Horner’s syndrome


Horner syndrome (also known as oculosympathetic palsy) is a rare neurological disorder that results from damage to the sympathetic nerves supplying the eye and face. It is characterized by a triad of clinical features: ptosis (drooping of the upper eyelid), miosis (constricted pupil), and anhidrosis (lack of sweating) on the affected side of the face.

Anatomy and Pathophysiology

The sympathetic innervation to the face and eyes is a three-neuron pathway:

  1. First-order neurons originate in the hypothalamus and descend through the brainstem and spinal cord to synapse in the ciliospinal center of Budge at the C8-T2 level.
  2. Second-order neurons exit the spinal cord and travel through the cervical sympathetic chain, ascend to the superior cervical ganglion.
  3. Third-order neurons project from the superior cervical ganglion, travel along the internal carotid artery and ophthalmic division of the trigeminal nerve, and innervate the dilator pupillae, Müller’s muscle of the upper eyelid, and the sweat glands of the face.

Damage to any part of this pathway can lead to Horner syndrome. Depending on the location of the lesion (first-, second-, or third-order), the associated signs and symptoms may vary.

Clinical Features

  1. Ptosis:

    • Mild drooping of the upper eyelid due to denervation of Müller’s muscle, a smooth muscle that aids in elevating the upper eyelid.
    • It is typically mild, unlike the complete ptosis seen in oculomotor nerve palsy.

  2. Miosis:

    • The affected pupil is constricted due to the loss of sympathetic input to the dilator pupillae muscle.
    • The affected pupil has a delayed response to light and dilates poorly in darkness, as parasympathetic innervation (which causes constriction) remains unopposed.

  3. Anhidrosis:

    • Loss of sweating on the affected side of the face. This is more prominent in lesions affecting the first- or second-order neurons, as third-order neuron lesions often spare sweating because the sympathetic fibers supplying the sweat glands travel along the external carotid artery, not the internal carotid artery.

  4. Enophthalmos (apparent sinking of the eye into the orbit):

    • Although this is often noted in textbooks, it is typically an illusion created by the ptosis and miosis, rather than an actual displacement of the eyeball.

Causes of Horner Syndrome

The etiology of Horner syndrome depends on the location of the lesion along the sympathetic pathway:

  1. First-order neuron lesions (Central Horner Syndrome):

    • Stroke (especially involving the brainstem)
    • Tumors (e.g., hypothalamic, brainstem, or spinal cord tumors)
    • Multiple sclerosis
    • Syringomyelia
    • Trauma

  2. Second-order neuron lesions (Preganglionic Horner Syndrome):

    • Pancoast tumor (lung apex tumor)
    • Trauma or surgery involving the neck or chest
    • Aortic dissection
    • Thoracic outlet syndrome
    • Neck masses

  3. Third-order neuron lesions (Postganglionic Horner Syndrome):

    • Carotid artery dissection (a common cause, associated with ipsilateral headache or neck pain)
    • Cavernous sinus thrombosis
    • Cluster headache
    • Trauma or surgery in the neck

Diagnosis

Horner syndrome is primarily a clinical diagnosis, but certain tests can help confirm the condition and localize the lesion.

  1. Cocaine Test:

    • Cocaine inhibits the reuptake of norepinephrine at the synapse in the dilator pupillae muscle, causing normal pupils to dilate. In Horner syndrome, the affected pupil fails to dilate.
    • A positive cocaine test confirms the diagnosis of Horner syndrome, but it does not localize the lesion.

  2. Apraclonidine Test:

    • Apraclonidine, an alpha-adrenergic agonist, reverses the miosis seen in Horner syndrome by causing dilation of the affected pupil (due to denervation hypersensitivity) and causing the normal pupil to constrict.
    • This is a more readily available and sensitive test compared to cocaine.

  3. Hydroxyamphetamine Test:

    • Hydroxyamphetamine stimulates norepinephrine release from third-order neurons. In third-order neuron lesions, the affected pupil will fail to dilate, whereas in first- or second-order lesions, both pupils will dilate normally.
    • This test helps localize the lesion to either a preganglionic or postganglionic cause.

  4. Imaging Studies:

    • MRI or CT of the brain, neck, and chest are often used to identify the underlying cause, especially if a tumor, stroke, or carotid dissection is suspected.
    • Chest X-ray may be used to rule out a Pancoast tumor in cases with suspected second-order neuron lesions.

Associated Syndromes

  • Pancoast Tumor: A lung cancer at the apex of the lung that invades the sympathetic chain, often associated with shoulder pain and arm weakness (due to brachial plexus involvement).
  • Carotid Artery Dissection: This is a medical emergency often associated with neck pain, headache, and possibly a stroke.
  • Cluster Headache: Patients with cluster headaches may develop transient Horner syndrome during a headache episode.

Treatment

The treatment of Horner syndrome is aimed at addressing the underlying cause, as there is no specific therapy for the syndrome itself.

  • Tumor-related Horner syndrome may require surgery, chemotherapy, or radiation depending on the tumor type.
  • Carotid dissection is treated with anticoagulation or antiplatelet therapy.
  • Cluster headaches are treated with medications like oxygen, triptans, or calcium channel blockers.
  • If Horner syndrome is due to a benign cause, it may not require specific treatment other than monitoring.

Prognosis

The prognosis of Horner syndrome depends largely on the underlying etiology:

  • Traumatic or post-surgical cases may resolve spontaneously.
  • Malignant causes (e.g., Pancoast tumor) may have a poorer prognosis depending on the stage and treatment response.
  • Carotid artery dissection is an important cause with a favorable prognosis if treated promptly.

Bibilography

  1. Biousse V, Touboul PJ, D’Anglejan-Chatillon J, Levy C, Schaison M, Bousser MG. Ophthalmologic manifestations of internal carotid artery dissection. Am J Ophthalmol. 1998;126(4):565-77.

  2. Freedman KA, Brown SM. Horner’s syndrome: clinical perspectives and update on pharmacologic testing. J Neuroophthalmol. 2005;25(3):136-42.

  3. Thompson HS, Kardon RH. Oculosympathetic paresis: the diagnostic utility of cocaine in Horner’s syndrome. Arch Ophthalmol. 2007;125(6):835-41.

  4. Choi JH, Park J, Kim JS. Acute brainstem infarction with Horner syndrome: lesion locations and proposed mechanisms. J Neurol Neurosurg Psychiatry. 2018;89(2):181-7.

  5. Roper-Hall G, Burdon MA, Moseley IF. Carotid artery dissection: recognition and management. J Neurol Neurosurg Psychiatry. 2011;82(2):151-9.

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