Asymmetric mydriatic response to topical tyramine in cluster headache relatives.

A pupillometric study was performed to evaluate the mydriatic response to tyramine, a noradrenaline releaser. There were three groups of subjects: (a) 10 cluster headache patients, in an asymptomatic period; (b) 20 of their close relatives, exempt from this disease; (c) 10 healthy controls. The tyramine was instilled into both eyes of each subject. The controls displayed an isocoric tyramine-induced mydriasis but the cluster headache sufferers and their relatives showed an anisocoric mydriasis. This anisocoric mydriasis was caused by a deficient mydriatic response on one side, which in the cluster patients corresponded to the symptomatic side. The sympathetic abnormality of the iris may be the expression of a functional asymmetry in the hypothalamus. Central sympathetic asymmetry could thus represent a dysgenetic family predisposition to lateralized headache attacks.