Description

• Horner syndrome presents as a classic triad of ipsilateral miosis, eyelid ptosis, and/or anhidrosis of the face and neck (with iris heterochromia in children).
• It is caused by the interruption of sympathetic nerve supply to the head, neck, and eye:
  • Central or preganglionic lesion (complete syndrome): 1st- or 2nd-order neuron
  • Peripheral postganglionic lesion (incomplete syndrome, no anhidrosis): 3rd-order neuron
• System(s) affected: Nervous; Skin/Exocrine
• Synonym(s): Bernard-Horner syndrome; Bernard syndrome; Horner's syndrome; Cervical sympathetic syndrome; Oculosympathetic syndrome; Oculosympathetic paralysis; Oculosympathetic deficiency; Oculosympathetic paresis

Epidemiology

• Predominant age: None
• Predominant sex: Male = Female

Incidence
Unknown

Prevalence
Unknown

Risk Factors

• Most common: Apical bronchogenic carcinoma (Pancoast tumor) in smokers
• Aneurysm of the carotid or subclavian artery
• Injuries to the carotid artery high in the neck
• Dissection of the carotid arteries
• Carotid artery occlusion:
  • 15% of patients with carotid artery occlusion develop ipsilateral Horner syndrome.
  • May occur without evidence of cerebral ischemia, neck injuries, or operative procedures
• Cluster headaches:
  • 20% have an ipsilateral Horner syndrome

Genetics
Rare autosomal dominant inheritance

Pathophysiology

• Constellation of signs produced when sympathetic innervation to the head, neck and eye is interrupted somewhere along the 3-neuron arc:
  • Absence of innervation of iris dilator and Müller muscles leads to miosis and slight ptosis, respectively.
  • Sympathetic innervation also controls sweat glands; interruption causes anhidrosis.
• Oculosympathetic pathway:
  • 1st-order neuron: Sympathetic nerve fibers originate in the hypothalamus, descend through the brainstem, and synapse at the ciliospinal center (of Budge) located at approximately the C8–T2 levels of the spinal cord.
  • 2nd-order neuron: Exits the spinal column at the T1 level primarily, arches over the apex of the lung and under the subclavian artery, ascending to the superior cervical ganglion at the level of the carotid bifurcation and angle of the jaw
  • 3rd-order neuron: Ascends along the adventitia of the internal carotid artery, through the cavernous sinus in proximity to cranial nerve [CN] VI, and joins CN V₁ to innervate the iris dilator muscle and Müller muscle in the eye.
• Sympathetic fibers innervating sweat glands and vasodilatory muscles branch off before the cervical sympathetic ganglion traveling along the external carotid artery, so distal lesions will not result in anhidrosis.
• Lesions anywhere along this pathway will lead to ipsilateral Horner syndrome.

Etiology

• Idiopathic (40%), congenital, or acquired
• Best classified by which order neuron is affected and by age (pediatric vs. adult)
• 1st-order neuron (13%):
  • Arnold-Chiari malformation
  • Basal meningitis (e.g., syphilis)
  • Basal skull tumors
  • Cerebral vascular accident: Lateral medullary (Wallenberg) syndrome
  • Cervical cord trauma
  • Demyelinating disease (multiple sclerosis)
  • Intrapontine hemorrhage
  • Neck trauma
  • Pituitary tumor
  • Syringomyelia
  • Unintended subdural placement of lumbar epidural catheter
• 2nd-order neuron (44%):
  • Aneurysm/Dissection of aorta
  • Central venous catheterization
  • Cervical rib
  • Chest tubes
  • Lymphadenopathy (Hodgkin, leukemia, tuberculosis, mediastinal tumors, sarcoid)
  • Mandibular tooth abscess
  • Neurofibromatosis type I and II
  • Pancoast tumor or infection of lung apex
  • Proximal common carotid artery dissection
  • Trauma/Surgical injury
• 3rd-order neuron lesions (43%):
  • Carotid cavernous fistula or other pathology
  • Carotid endarterectomy or carotid artery stenting
  • Cluster headaches
  • Internal carotid artery dissection
  • Herpes zoster
  • Lesions of the middle ear (acute otitis media)
  • Nasopharyngeal cancer
  • Tonsillectomy
  • Raeder paratrigeminal syndrome
• Drugs: Acetophenazine, alseroxylon, bupivacaine, butaperazine, carphenazine, chloroprocaine, deserpidine, diacetylmorphine, diethazine, ethopropazine, etidocaine, guanethidine, influenza virus vaccine, levodopa, lidocaine, mepivacaine, mesoridazine, methdilazine, methotrimeprazine, oral contraceptives, perazine, prilocaine, procaine, prochlorperazine, promazine, propoxycaine, reserpine, thioproperazine, thioridazine, trifluoperazine

Pediatric Considerations
2nd-order neuron lesion is most common etiology: Birth trauma to neck and shoulder, chest surgery, neuroblastoma (paraspinal), and vascular anomalies of the carotid arteries

Commonly Associated Conditions

• Wallenberg syndrome
• Pancoast tumor
• C8 radiculopathy