False-negative hydroxyamphetamine (Paredrine) test in acute Horner's syndrome.

PURPOSE: To describe a false-negative hydroxyamphetamine test.

METHOD: Two patients with acute unilateral Horner's syndrome whose pupils initially dilated equally to hydroxyamphetamine had pharmacologic localization to the postganglionic nerve in the second week following the onset of symptoms.

RESULTS

Neuroimaging confirmed the postganglionic location in both cases.

CONCLUSION

Falsely negative localization with hydroxyamphetamine can occur during the first week after injury, during which time the function of the boutons at the presynaptic terminal is lost.