Cluster headache without autonomic symptoms: why is it different?

BACKGROUND Some patients with otherwise typical cluster headache (CH) have persistent attacks free of cranial autonomic symptoms (CAS). The factors responsible for this atypical presentation are not known. OBJECTIVES To identify factors associated to the absence of CAS in patients with CH. METHODS A prospective series of 157 patients with the diagnosis of CH was analyzed, comparing 148 typical CH patients with 9 CH patients without CAS. RESULTS Patients without CAS reported significantly less intense attacks (P = .003) when compared to those with CAS. There was also a tendency (not reaching statistical significance) for a higher frequency of females and chronic CH among those without CAS. Otherwise, there were no differences between the two groups (in age, duration of illness, follow-up time, attack duration or frequency, nor side or site of pain). A logistic regression analysis showed that only pain intensity could explain the difference between the two groups, since the other explanatory variables were also associated with different intensity of attacks. CONCLUSIONS These results support the hypothesis that CH without cranial autonomic symptoms represents a milder form of CH.