Background.—Alteration of circadian rhythmicity involving several endocrinologic and autonomic parameters has been observed in cluster headache.
Objectives.—To explore whether circadian failure of the pain control system may exist in cluster headache.
Methods.—The nociceptive flexion reflex threshold was studied in 25 patients with episodic cluster headache (14 active, 11 in remission) and 6 patients with chronic cluster headache, along with 10 normal volunteers throughout a 24-hour period. The reflex response was evoked at the level of the biceps femoris by stimulating the sural nerve at the ankle. Single and population mean cosinor methods were used to detect the circadian rhythmicity.
Results.—In the patients with episodic cluster headache, a significant reduction in the nociceptive flexion reflex threshold was observed in both the active subgroup and the subgroup in remission (P<.05). In these patients, persistence of a significant 24-hour rhythm during both the active period and remission was observed, but a shift of the phase was observed during clinical activity when compared with the remission period. A lack of circadian nociceptive flexion reflex threshold rhythmicity was found in the patients with chronic cluster headache.
Conclusions.—Our findings suggest that in cluster headache there may be impairment of the pain control system that is associated with periodic failure of the mechanisms involved in the organization of biological rhythms.