Horner syndrome

Horner syndrome (HS) is a neurological disorder characterized by a symptom triad of miosis (an abnormally small pupil), partial ptosis (drooping of the upper eyelid), and facial anhidrosis (absence of sweating). This condition results from lesions that interrupt the ipsilateral sympathetic nervous supply to the head, eye, and neck. Most cases of HS are idiopathic, but conditions such as brainstem stroke, carotid dissection, and neoplasm are occasionally identified as the cause of HS. Because of the wide array of possible causes, diagnosis of the underlying disorder frequently poses a challenge and requires a systematic approach. Once the lesion has been identified, treatment should be tailored to the specific cause.

• Triad of Horner syndrome
  • Miosis (constriction of the pupil)
    • Occurs because the sympathetically controlled iris dilator muscle fails to contract
    • Leads to anisocoria and a dilation lag on exam
  • 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
• (Apparent) enophthalmos
• Associated symptoms depending on the etiology:
  • Atrophy of arm and hand muscles
  • Pain in the neck or face

Remember the symptoms of Horner syndrome by the great HORNs of the PAMpas deer: Ptosis, Anhidrosis, and Miosis.