Description

• A constellation of neurological signs and symptoms manifested as a classic triad of ipsilateral miosis, eyelid ptosis, and anhidrosis of the ipsilateral face and/or neck (with iris heterochromia in children)
• System(s) affected: nervous, skin/exocrine
• Synonym(s): Bernard syndrome

Epidemiology

Incidence

• Estimated incidence of pediatric Horner syndrome is 1.42 per 100,000 in patients <19 years of age with a birth prevalence of 1 in 6,250 for those with congenital onset of Horner syndrome.
• Incidence in adults is not known.

Etiology and Pathophysiology

• A lesion affecting the neurons in the sympathetic chain (first, second, or third order) may produce signs and symptoms of Horner syndrome as a result of a lack of sympathetic input to the orbit.
  • Ptosis: Sympathetic innervation to the Müller muscle in the upper eyelid and the lower eyelid retractors helps to maintain normal eyelid position. When sympathetic innervation to these structures is interrupted, a subtle ptosis of both the upper lid (ptosis) and lower lid (reverse ptosis) may result. This ptosis may be subtle, often ≤2 mm.
  • Meiosis: The radially oriented pupillary dilator muscle produces pupillary dilation in response to stimulation by the sympathetic nervous system. Anisocoria will be more pronounced in dim lighting, reflecting impairment of dilation in the affected eye. The affected eye will constrict normally in response to light but will be slower to dilate than the unaffected pupil.
  • Anhidrosis: When present, anhidrosis may assist in localizing a lesion. Sympathetic fibers innervating sweat glands of the lower face and vasodilatory muscles branch off before the superior cervical sympathetic ganglion and travel along the external carotid artery. Lesions affecting primary and secondary neurons are more likely to produce anhidrosis of both the upper and lower face.
• Etiologies in adults:
  • Arnold-Chiari malformation, basal meningitis (e.g., syphilis), cerebral vascular accident, lateral medullary (Wallenberg) syndrome, cervical cord trauma, cervical spondylosis, demyelinating disease (multiple sclerosis), intrapontine hemorrhage, neck trauma, syringomyelia/syringobulbia, tumor (basal skull, pituitary), unintended subdural placement of lumbar epidural catheter
  • Aneurysm/dissection of aorta, central venous catheterization, chest tubes, 1st rib fracture, lymphadenopathy (Hodgkin lymphoma, leukemia, tuberculosis, sarcoidosis), mandibular tooth abscess, neuroblastoma, Pancoast tumor or infection of the lung apex, proximal common carotid artery dissection, thoracic outlet obstruction (cervical rib, subclavian artery aneurysm), trauma/surgical injury, tumor (thyroid, mediastinum)
  • Carotid cavernous fistula or other pathology, carotid endarterectomy or carotid artery stenting, cluster headaches/paroxysmal hemicrania, internal carotid artery dissection, herpes zoster virus infection, lesions of the middle ear (acute otitis media), Lyme disease, tumor (nasopharyngeal, pituitary, paratrigeminal, metastasis, skull base), tonsillectomy, trauma/surgical injury, Raeder paratrigeminal syndrome
• Etiologies in children:
  • Birth trauma/neck trauma (injury to the brachial plexus)—most common; brainstem glioma, neuroblastoma, vascular anomalies, surgical interventions in the neck/chest, idiopathic

Genetics
Rare autosomal dominant inheritance

Risk Factors

• Recent trauma to the head/neck/thorax (e.g., motor vehicle accidents)
• Smoking (Pancoast tumor)
• Known aneurysm of the carotid or subclavian arteries
• Known malignancy/tumor/mass
• Previous surgery (neck/thoracic)
• Cluster headache