J N Blau and H O Engel (Sept 18, p 1001)1 describe a new clusterheadache precipitant—increased body heat, from the environment, a hot bath, or central heating in 52 (26%) of 200 patients, and from exercise in 23 (12%) patients (three by sexual intercourse).

The causes of cluster headache are still unknown; the temporal pattern of the cluster periods suggest the involvement of central structures in particular the hypothalamus, which regulates circadian rhythms. The pineal gland through melatonin secretion plays a central part in the circadian organisation of biological rhythms. Evidence obtained in animals suggests that the pineal gland and melatonin may be related to the regulation of core body temperature. Dependent on the species considered, melatonin has a part in the generation of seasonal rhythms of daily torpor and hibernation, in heat stress tolerance, and in setting the core body temperature set point. In human beings, the circadian rhythm of melatonin is closely associated with that of core body temperature, the nocturnal decline of this temperature being inversely related to the rise of melatonin.2 Chazot and colleagues3 reported lower melatonin concentrations in cluster-headache patients than in controls. Waldenlind and colleagues4 also show lower concentrations in the cluster period than remission.

Increased body heat might precipitate cluster-headache attacks by alteration of melatonin concentrations, leading to hypothalamic dysregulation and chronobiological dysfunction. These findings also support a therapeutic option of melatonin in the prophylaxis of cluster headache 5.