Apraclonidine for the pharmacologic confirmation of acute Horner syndrome.

Apraclonidine is the most widely used pharmacologic agent to confirm Horner syndrome. It is a strong α-2 and a weak α-1 adrenergic agonist and reversal of anisocoria is considered a positive test. The utility of apraclonidine in acute Horner syndrome remains controversial as the exact timing for denervation sensitivity to develop remains unknown. The goal of this study was to describe the use of apraclonidine in the diagnosis of acute Horner syndrome in patients with an unequivocal onset within 7 days. We identified 3 patients who were referred to ophthalmology/neuro-ophthalmology service and had reversal of anisocoria within 7 days. Two cases of second-order Horner syndrome after cardiac surgery and a case of a third-order Horner syndrome from a carotid cavernous sinus fistula resulted in reversal of anisocoria 72 h, 48 h, and 5 days after onset. Photographic documentation was provided for all cases. Our results suggest that apraclonidine has utility in the acute period and positive results can be seen as early as 48 h after onset. Apraclonidine should therefore still be considered to confirm the presence of acute Horner syndrome before extensive neuroimaging is performed.