Cluster headache and periodic affective illness: common chronobiological features.

Many of the seasonal changes occurring in animals appear to be associated with photoperiodic modifications, and particularly with the duration of the phases of exposure to light and dark. The integration of these processes is made possible by the normal functioning of biological oscillators or synchronizers, presumably located at the hypothalamic level. Cluster headache (CH), seasonal affective disorder (SAD) and bipolar mood disorders are conditions bearing numerous analogies, particularly as regards the temporal pattern of disturbances, the nature of predisposing or precipitating factors, the peculiar relationship with sleep, the neuroendocrine findings, and the clinical response to current treatments. The secretion of melatonin, which is influenced by the light/dark cycle, displays a bimodal pattern, which is likely to be dictated by the activity of distinct synchronizers for light and dark. Changes in the secretory pattern of this neurohormone have also been documented in both CH and SAD. The possibility of normalizing the secretory rhythm of melatonin by means of phototherapy in SAD, and the therapeutic use of the hormone to prevent the recurrence of active phases in CH, represent further interesting similarities between these two disorders. Melatonin, acting as a unique neuroendocrine transductor of photic inputs, may therefore be viewed as a marker of dyschronic disease to be used in patients suffering from CH and affective illness, for both diagnostic purposes and to assess the response to pharmacological and non pharmacological treatments.