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Cocaine testing often unnecessary to confirm Horner’s syndrome
Drug is not always readily available, and it is sometimes difficult to determine its potency. Testing can help determine what areas should be scanned to detect lesions.
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OTTAWA — Pharmacological testing for Horner’s syndrome is not always necessary to confirm a diagnosis, according to a professor who spoke at the Sally Letson Symposium, whose theme this year was neuro-ophthalmology.
Anthony C. Arnold |
Speaking in a debate over the merits of pharmacological testing for Horner’s syndrome, Anthony C. Arnold, MD, professor of ophthalmology at the Jules Stein Eye Institute of the University of California, Los Angeles, said there are challenges in doing cocaine testing, such as the availability of the drug and its potency.
“It is a controlled substance,” Dr. Arnold told an audience of ophthalmologists. “It is not always readily available. If you are practicing in the community, how will you get it? Even if testing can wait, you do not know how potent it is after it has been sitting in a vial for 31 days.”
In Horner’s syndrome, which is characterized by normal light reaction and greater anisocoria in the dark, pharmacological testing involves the use of cocaine to confirm the diagnosis or detect asymmetry and the use of hydroxyamphetamine to localize the lesion as post-ganglionic (third-order) or pre-ganglionic (first- or second-order), if the cocaine test is positive.
Liquid cocaine is applied topically to determine how pupils dilate. Whereas a normal pupil will dilate, a Horner’s pupil will dilate poorly because of the lack of endogenous norepinephrine at the nerve ending.
“Confirming that you have a Horner’s syndrome [with pharmacological testing] is often unnecessary,” Dr. Arnold said. “It is usually a clinical diagnosis.”
A positive endpoint is regarded as residual anisocoria greater than 0.8 mm after administration of cocaine or can also be regarded as positive if there is an increase in the anisocoria by 1 mm, he said. He characterized the endpoint as unclear and stressed that the test lacks sensitivity and specificity.
“The problem is, how do you interpret the result?” Dr. Arnold said. “The endpoint is unclear. We also do not know how accurate the test is.”
Dr. Arnold challenged the notion of how lesions are classified as benign or not depending on their location on the sympathetic pathway three-neuron arc. Pre-ganglionic lesions are conventionally thought of as not benign, while post-ganglionic lesions are thought of as benign.
If the pupil does not dilate with the administration of hydroxyamphetamine, the Horner’s syndrome is deemed post-ganglionic. If it does, it is deemed pre-ganglionic.
“We have been taught that central [first-order] or [second-order] pre-ganglionic Horner’s are bad, and post-ganglionic Horner’s are good,” he said. “Just because you localize the lesion as post-ganglionic does not mean that it is good. Most carotid dissections are post-ganglionic lesions.”
Julie Falardeau, MD, an assistant professor of neuro-ophthalmology at the Casey Eye Institute at Oregon Health & Science University in Portland, Ore., said pharmacological testing assists in the diagnosis of Horner’s syndrome and in determining what areas should be scanned to detect lesions.
“Structural lesions can be missed by even the most experienced radiologists,” Dr. Falardeau said, noting that distinguishing between a pre-ganglionic lesion and a post-ganglionic lesion is significant for patient prognosis.
She noted that in children with Horner’s syndrome, however, hydroxyamphetamine is not a reliable agent to use.
For more information:
- Anthony C. Arnold, MD, can be reached at the Jules Stein Eye Institute, 100 Stein Plaza, Los Angeles, CA 90095-7005; 310-825-4344; e-mail: arnolda@ulca.edu.
- Julie Falardeau, MD, can be reached at the Casey Eye Institute, Oregon Health & Science University, 3375 SW Terwilliger Blvd., Portland, OR, 97239; 503-494-3687; fax: 503-494-4286; e-mail: falardea@ohsu.edu.
- Louise Gagnon is an OSN Correspondent based in Whitby, Ontario, Canada.