Horner's syndrome Flashcards
(12 cards)
What is Horner’s syndrome
Horner’s syndrome describes the specific ophtalmic changes associated with loss of the sympathetic supply to the orbit
- when the sympathetic nerves controlling one of the eyes are damaged, only the parasympathetic nerves work and Horner’s syndrome is created
What are the clinical signs associated with Horner’s syndrome
Horner’s syndrome consists of five signs:
- constricted pupil (= miosis)
- elevated third eyelid
- retraction of the eyeball into the head (=enophtalmos)
- slight ptosis (drooping) of the upper eyelid and decreased tone of the lower eyelid
- increased pink color and warmth of the ear and nose on the affected side (very hard to detect in small animals)
These signs appear on the side of the face (and eye) with damaged sympathetic nerves
- depending on the lesion type not all features may be present
What are the respective role of the parasympathic and sympathetic nervous system
The parasympathetic system maintains a status quo, a normal business-as-usual state
The sympathetic system prepares the body for a fight or flight situation
What is the role of the sympathetic nerve fibers in the eye
In the eye, the sympathetic nerve fibers:
- dilate the pupil
- widen the eyelids
- drop the third eyelid
- keep the eye in a forward position in the socket
What is the action of the parasympathetic nerve fibers in the eye
The parasympathetic nerves:
- constrict the pupil
- raise the third eyelid
- retract the eye for protection
How is the sympathetic pathway of the eye organised
The sympathetic innervation of the head and eye consists of first, second and third order neurons
First order neurons originate in the hypothalamus and rostral midbrain and continue down the spinal coord, down the length of the neck, and just into the chest
The synapse between the first and second order neurons occurs in the lateral horn of the spinal cord grey matter at the level of first to third thoracic spinal cord segments
- the second order axons exit the spinal cord with the first to third thoracic nerve roots and make a U-Turn and travel back towards the eyes
- the nerves form right and left bundles that are called “pre-ganglionic segments” and they extend from the top of the chest back to the area of the middle ear
The synapse between the second and third order neurons occurs in the cranial cervical ganglion adjacent to the tympanic bulla
- from here, the third order sympathetic axons pass through the middle ear and enter the cranial cavity with the glossopharyngeal nerve and travel to the eye
- third order neurons are called post-ganglionic segment
How can you confirm Horner’s syndrome
In any animal presenting with anisocoria suggestive of Horner’s syndrome, the first step is to confirm that the clinical findings are in fact Horner’s syndrome
This can be perform by answering those questions:
- Is the animal blind?
- Horner’s syndrome will not interfere with vision
- Does the smaller pupil dilate in the dark?
- the miotic pupil will not dilate substantially in the dark while the normal larger pupil will dilate
- Horner’s syndrome is the only neurological cause of anisocoria that becomes more pronounced in the dark
- Does the larger pupil constrict in light?
- the larger pupil is the normal pupil and should constrict when a bright light is shone into it
- if no constriction is observed then there is a lesion of the parasympathetic portion of the oculomotor nerve CN III
- Are there other signs of CN III deficits?
- if the innervation to the extraocular muscles is also affected there will be a lateral strabismus
Explain pharmacological testing to predict the site of the lesion in Horner’s syndrome
In cases where Horner’s syndrome has been present for some time (usually at least 7 to 14 days), denervation hypersensitivity resulting from the sympathetic denervation allows pharmacological testing to be performed to predict the site of the lesion based on increased sensitivity to topical phenylephrine
The time to pupillary dilation, following administration of 1% phenylephrine topically in both eye, is determined
- the shorter the time to pupillary dilation, the closer the lesion is to the iris:
- less than 20 minutes suggests third order Horner’s syndrome
- 20 to 45 min suggests second order
- 60 to 90 min suggests firstt order Horner’s syndrome or no sympathetic denervation of the eye
What are the main clinical syndromes that may mimic Horner’s syndrome
Uveitis
- there would be painful eye, aqueous flare and swelling of the iris
Pourfour du Petit syndrome (excessive sympathetic tone to the eye)
- mild pathological insult to the sympathetic supply to the head (most likely adjacent to the middle ear) may lead to irritation of the sympathetic fibres resulting in sympathetic hyperactivity rather than sympathetic denervation
Dysautonomia
- should be suspected with bilateral pupillary dilation that is not responsive to light, protrusion of the third eyelids, decreased tear production and dry mouth and nose, in the presence of normal vision
- most cases will also have systemic signs, most commonly affecting the GI tract and urinary system
What are the main causes for first order lesions
Neoplasia of the brain
Vascular accidents
Fibrocartilaginous embolism/disk extrusion
What are the main causes for second order lesions
Brachial plexus disease
A mass in the chest (e.g., tumor or fungal granuloma)
Neck trauma
What are the main causes for third order lesions
Ear diseases
- bacterial otitis media
- neoplasia
