The International Headache Society (IHS) defines cluster headache (CH) as a severe, strictly unilateral headache lasting 15 min to 3 h and occurring at a frequency ranging from once every other day to eight times daily. The attacks are associated with at least one cranial autonomic feature or restlessness. CHs appear to be linked to the circadian clock, and many sufferers have circadian periodicity-in particular, a propensity for nocturnal attacks. The attacks occur in periodic bouts in the majority of patients.OBJECTIVE
To investigate whether the present IHS criteria for the diagnosis of CH should be applied with more flexibility in clinical practice.DESIGN AND INTERVENTION
The investigators conducted a nationwide survey in The Netherlands of patients with IHS-defined CH and those with a clinical picture resembling CH. A total of 1,452 individuals-recruited between May 1998 and March 2001-filled in two questionnaires that contained items concerning the IHS criteria for CH and additional features, such as circadian attack patterns. The clinical characteristics of patients who satisfied all the diagnostic criteria of the IHS (n = 1,163; IHS-CH group) were compared with those of patients who met all but one of the criteria (n = 289; IHS-CH-1 group). Patients in the two groups had a similar mean age at headache onset, but the male-to-female ratio was lower in the IHS-CH-1 group (P <0.001).OUTCOME MEASURES
The main outcome measures were the clinical features of survey participants.RESULTS
Most patients in the IHS-CH-1 group (n = 185, 64%) failed the IHS definition for CH because their attacks exceeded 3 h (median duration 5 h, range 190 min to 5 days). In total, 42% of the patients who tended to have longer attacks reported that some of their attacks were shorter than 3 h, thereby fulfilling the IHS criteria for CH. Other symptoms that typically accompany CH were less frequent among patients who reported attacks exceeding 3 h than in patients who met all the IHS criteria (P <0.005): circadian rhythm 49% versus 64%, nocturnal attacks 67% versus 78%, episodic pattern 65% versus 78%, and restlessness during attacks 64% versus 76%. Migraine-like symptoms, however, were more common among patients with longer attack duration than in patients who had IHS-defined CH (P <0.005): nausea 38% versus 27%, and photophobia or phonophobia 67% versus 54%. The second most common reason for failing the IHS definition was an attack frequency of less than once every other day (n = 46, 16%; mean two attacks per week); the individual attacks in these patients, however, satisfied the IHS criteria for CH.CONCLUSION
Patients with headaches lasting longer than 3 h who meet other IHS criteria for the diagnosis of CH, such as restlessness or episodic pattern, could benefit from CH-specific treatment. Attack frequency might not be a useful criterion for the diagnosis of CH.