Will a pre-ganglionic or post-ganglionic Horner's syndrome dilate with Hydroxyamphetamine?

Will a pre-ganglionic or post-ganglionic Horner's syndrome dilate with Hydroxyamphetamine?

• A. Pre-ganglionic
• B. Post-ganglionic
• C. Both
• D. Neither

Answer: (A)

Hydroxyamphetamine works by prompting release of norepinephrine from the postganglionic nerve endings. In Horner syndrome, a preganglionic lesion (before the superior cervical ganglion) leaves the postganglionic neuron intact. When hydroxyamphetamine is given, the intact postganglionic terminals can release NE, restoring sympathetic stimulation to the iris dilator and causing pupil dilation on the affected side. If the lesion is postganglionic, the postganglionic neuron or its terminals are damaged, so there’s no NE to release and no dilation occurs. Thus, dilation with hydroxyamphetamine points to a preganglionic lesion.

Hydroxyamphetamine works by prompting release of norepinephrine from the postganglionic nerve endings. In Horner syndrome, a preganglionic lesion (before the superior cervical ganglion) leaves the postganglionic neuron intact. When hydroxyamphetamine is given, the intact postganglionic terminals can release NE, restoring sympathetic stimulation to the iris dilator and causing pupil dilation on the affected side. If the lesion is postganglionic, the postganglionic neuron or its terminals are damaged, so there’s no NE to release and no dilation occurs. Thus, dilation with hydroxyamphetamine points to a preganglionic lesion.