Localization of Horner's syndrome. Use and limitations of the hydroxyamphetamine test

The pupillary response to hydroxyamphetamine eye-drops has been advocated as a test for sub-dividing patients with Horner's syndrome into those with lesions of the 1st or 2nd sympathetic neurone (normal dilatation) and those with lesions of the 3rd neurone (no or minimal dilatation). We compared the response of the right and the left eye in 40 control subjects and also in 25 consecutive patients with Horner's syndrome from a known lesion. In the controls, 1 eye might dilate up to 1.0 mm less than the other. In the patients, abnormally weak dilatation (difference with the other eye more than 1.0 mm) occurred only with lesions of the 3rd neurone, but in only 4 of 10 such cases. Of the other 6 patients with a lesion of the 3rd neurone, 2 had a minimal response of the normal eye, and 4 showed subsequent recovery of oculosympathetic function (which suggests that denervation had not occurred). In conclusion, an abnormal hydroxyamphetamine test reliably indicates a lesion of the 3rd neurone, but a normal test provides little diagnostic aid.