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Haw's Syndrome - Issue Description

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Issue Name

Bernard-Horner Syndrome

Other Names
Bernard-Horner Syndrome, Horner's Syndrome, HS, Oculosympathetic Palsy

Issue Description

Horner's Syndrome is a group of signs that occurs when specific muscles of the face lose their stimulation by certain nerves, specifically the sympathetic nerves. It is caused by some type of injury to, or lesion of, the nerves. The injury may occur at the level of the brain, upper spinal cord, or between the spinal cord and the face.


Horner's syndrome consists of five signs:

  • Constricted Pupil
  • Elevation of the Third Eyelid
  • Retraction of the eyeball into the head
  • Slight drooping of the Eyelid
  • Increased pink color and warmth of the ear and nose on the affected side (very hard to detect in small animals)

  • All these signs are caused by damage to sympathetic nervous system as it supplies the eye on the affected side of the head.


    Localizing which area of the sympathetic nerve system is affected goes a long way in determining the nature of the damage as different areas of the system are prone to different types of injury. Special eye drops can be used to stimulate different areas of the nervous system and determine if the lesion is in the first nerve segment or in the second nerve segment. Most are in the second nerve segment.

    With second nerve segment involvement:
    If ear infection is not obvious and disease of the eye beyond the Horner's syndrome itself is not obvious, then it is probably prudent to allow the syndrome to resolve on its own. This usually occurs within 6-8 weeks. Further diagnostics may be undertaken if new developments occur or if the syndrome persists beyond this time.

    With first nerve segment involvement:
    Involvement of the first nerve segment indicates a problem in the chest or spinal cord and is more significant. Chest radiographs should be taken to rule out cancer spread to the chest (the only sign of this may be the Horner's syndrome). The front leg should be carefully checked for evidence of function loss as a tumor or protruding intervertebral disc could be exerting pressure on the spinal cord. Trauma to the neck as with a strong jerk from a collar or straining against a leash can also produce Horner's syndrome from this section of the nerve. Generally more diagnostic work is needed for cases involving the first nerve segment as there is potential for more serious underlying causes. If the syndrome stemmed from pulling on the leash, it should resolve uneventfully depending on how badly damaged the nerve is.


    In dogs, the most common causes are:

  • Idiopathic (cause unknown)
  • Car accidents with trauma to the head, neck, or chest
  • Bite wounds
  • Intervertebral (IV) disc disease in the neck area
  • Infections of the middle ear
  • Disease of the orbit (area behind the eye)
  • Cancer involving the brain or chest
  • As a result of a treatment (e.g.; ear cleaning) or medication
  • Treatment

    It is not necessary to treat Horner's syndrome. The syndrome is not painful and does not interfere with vision. The significance of the syndrome is that it indicates nerve damage which must be recognized. If one wishes to treat the syndrome for cosmetic reasons, phenylephrine eye drops can be prescribed to relieve clinical signs.

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