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.
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.
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.
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.