Bilateral Horner's syndrome in cluster type headaches.

A patient with cluster type headaches demonstrated bilateral and alternating ocular sympathetic dysfunction during a spontaneous as well as a nitroglycerin-induced attack. Biochemical evaluation revealed postganglionic pupillary dysfunction on the symptomatic side and preganglionic pupillary dysfunction contralaterally. These findings defy a simple explanation regarding a central or peripheral origin of the oculocephalic sympathetic dysfunction.