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