| HORNER'S SYNDROME  SIGNS AND SYMPTOMS
Horner's syndrome is characterized by an interruption of the
oculosympathetic nerve pathway somewhere between its origin in the hypothalamus and the
eye. The classic clinical findings associated with Horner's syndrome are ptosis, pupillary
miosis and facial anhidrosis. Other findings may include apparent enophthalmos, increased
amplitude of accommodation, heterochromia of the irides (if it occurs before age two),
paradoxical contralateral eyelid retraction, transient decrease in intraocular pressure
and changes in tear viscosity.
Horner's syndrome has no predilection for age, race, gender or
geographic location. Horner's syndrome of congenital origin is typically around the age of
two years with heterochromia and absence of a horizontal eyelid fold or crease in the
ptotic eye. Iris pigmentation (which is under sympathetic control during development) is
completed by the age of two, making heterochromia an uncommon finding in Horner's
syndromes acquired later in life. Old photographs can aid the clinician in distinguishing
congenital Horner's by documenting heterochromia present at, or near, birth.
PATHOPHYSIOLOGY
Sympathetic innervation to the eye consists of a three neuron arc. The first neuron
originates in the hypothalamus. It descends and travels between the levels of the eighth
cervical and forth thoracic vertebrae (C8-T4) of the spinal cord. There, it synapses with
second order neurons whose preganglionic cell bodies give rise to axons. These axons pass
over the apex of the lung and enter the sympathetic chain in the neck, synapsing in the
superior cervical ganglion. Here, cell bodies of third order neurons give rise to
postganglionic axons that course to the eye via the cavernous sinus. These sympathetic
nerve fibers course anteriorly through the uveal tract and join the fibers of long
posterior ciliary nerves to innervate the dilator of the iris. Postganglionic sympathetic
fibers also innervate the muscle of Mueller within the eyelid, which is responsible for
the initiation of eyelid retraction during eyelid opening. Postganglionic sympathetic
fibers, responsible for facial sweating, follow the external carotid artery to the sweat
glands of the face. Interruption at any location along this pathway (preganglionic or
postganglionic) will induce an ipsilateral Horner's syndrome.
The common etiologies of acquired preganglionic Horner's syndrome
include, but are not limited to, trauma, aortic dissection, carotid dissection,
tuberculosis and Pancoast tumor. Common causes of post-ganglionic Horner's syndrome
include trauma, cluster migraine headache and neck or thyroid surgery.
The diagnosis and the localization of a Horner's syndrome is
accomplished with pharmacological testing. Ten percent liquid cocaine (topically applied),
works as an indirect acting sympathomimetic agent by inhibiting the re-uptake of
norepinephrine at the nerve ending. A Horner's pupil will dilate poorly because of the
absence of endogenous norepinephrine at the nerve ending. The test should be evaluated
thirty minutes after the instillation of the drops to ensure accuracy. The cocaine test is
used to confirm or deny the presence of a Horner's syndrome. However, a positive cocaine
test does not localize the lesion.
To localize the lesion as either preganglionic or postganglionic,
Paradrine 1% (hydroxyamphetamine) or Pholedrine 5% (n-methyl derivative of
hydroxyamphetamine) can be instilled 48 hours later. Pholedrine and Paradrine act
similarly by producing the forced release of endogenous norepinephrine from the
presynaptic vesicles. If the third neuron is damaged, there will be no endogenous
norepinephrine and the pupil will not dilate, thus indicating a postganglionic lesion.
Dilation indicates first or second order neuron lesion. There is currently no method of
topical testing to differentiate a first order preganglionic lesion from a second order
preganglionic lesion.
MANAGEMENT
In general, the treatment for Horner's syndrome depends upon the cause. In many cases
there is no treatment that improves or reverses the condition. Treatment in acquired cases
is directed toward eradicating the disease that is producing the syndrome. Recognizing the
signs and symptoms is tantamount to early diagnosis and expedient referrals to
specialists.
CLINICAL PEARLS
The time frame for testing is important because cocaine
has the ability to inhibit the uptake of Pholedrine and Paradrine into the presynaptic
vesicle, reducing accuracy. There must be at least 48 hours between the tests.
Some of the older literature suggests employing
Phenylephrine 1% solution for localization. This technique is rarely employed because
patients with either preganglionic or postganglionic lesions become hypersensitive to the
drug making results inaccurate.
There is a "dilation lag" in Horner's syndrome
where the involved pupil will dilate slowly in dim illumination. That is, the degree of
anisocoria diminishes as the patient sits in a dark room.
Post-ganglionic Horner's syndromes tend to occur from
more benign causes and are typically vascular in origin.
If hemianalgesia and/or hemiparesis appear with Horner's
syndrome, then the lesion is within the spinal cord or brain.
Isolated Horner's syndrome typically is vascular in
nature.
Other reports in this section
|
