The chronic variant can be found in 10-20% of all cluster headache patients. While circadian and circannual rhythmicity are characteristic of the episodic variant, little is known on chronobiology in chronic cluster headache. We report a patient with chronic cluster evolved from episodic who recorded a total of 5447 attacks over 10 years. After spectral analysis, cosinor models were calculated within the frequency ranges of 23-25 h (circadian) and 11-13 months (circannual), respectively. Significant results (P <0.01) were found for 24-h periods, but not for circannual intervals (12 months). However, with regard to circannual periodicity, a semi-circannual rhythm (5-7 months) was suitable for curve fit and yielded significant results in the cosinor analysis at 6 months (P <0.05). This remarkable long observation period of 10 years shows that, at least for secondary chronic cluster headache which evolved from the episodic form, a typical circadian and circannual rhythmicity comparable to that of episodic cluster headache exists.
