Pathophysiology

Central

• Anatomical trajectory: Hypothalamus (first-order oculosympathetic neuron) → brainstem, cervical, and thoracic spinal cord → ciliospinal center (C8–T2)
• Typical lesions:
  • Brainstem stroke (e.g., Wallenberg syndrome)
  • Cervical Neuroloy physioloy injury (e.g., Brown-Séquard syndrome, syringomyelia)
  • Brain tumors
  • Brainstem (pontine) hemorrhage
  • Demyelinating disease (e.g., multiple sclerosis)
  • Malformations (e.g., Arnold-Chiari)
  • Meningitis

Preganglionic

• Anatomical trajectory: Ciliospinal center (second-order oculosympathetic neuron) → pulmonary apex → stellate ganglion → superior cervical ganglion
• Typical lesions:
  • Tumors (e.g., breast or lung cancer compressing stellate ganglion, esp. Pancoast tumor)
  • Iatrogenic (e.g., birth trauma, central venous catheterization)
  • Lymphadenopathy
  • Arterial lesions/dissection: aorta, subclavian, common carotid
  • Cervical rib

Postganglionic

• Anatomical trajectory: Superior cervical ganglion (third-order oculosympathetic neuron) → internal carotid artery and ophthalmic nerve → iris dilator muscle
• Typical lesions:
  • Dissection of the internal carotid artery
  • Cluster headache
  • Cavernous sinus syndrome
  • Tumor
  • Herpes zoster infection

Clinical features

• Triad of Horner syndrome
  • Miosis (constriction of the pupil)
    • Occurs because the sympathetically controlled iris dilator muscle fails to contract. See Pupillary light reflex.
    • Leads to anisocoria and a dilation lag on exam
      • More noticeable in the dark when the sympathetic tone is increased
  • Partial ptosis (drooping of the upper eyelid)
    • Occurs because the sympathetically controlled superior tarsal muscle fails to keep the upper eyelid raised
    • It is milder than ptosis associated with oculomotor nerve or levator palpebrae muscle lesions.
  • Anhidrosis (absence of sweating) or reduced sweating on the face and arm, depending on the location of the lesion
    • Occurs because the sympathetic innervation of the facial sweat glands is impaired
    • Seen in central and preganglionic lesions
• Facial flushing due to vasodilatation
  • Occurs because the vasoconstrictive effect of the sympathetic nervous system is lost.
• (Apparent) enophthalmos
• Associated symptoms depending on the etiology:
  • Atrophy of arm and hand muscles
    • Infiltration of the brachial plexus causes pain (plexus neuralgia), as well as motor and sensory deficits in the arm.
  • Pain in the neck or face