Lack of seasonal variation in menstrually-related migraine.

The aim of the study was to study seasonal variation in migraine headache in a group of women with menstrually-related migraine (MRM) compared with non-menstrual migraine. Via newspaper advertisement, women with migraine living in North Norway were invited. The patients were included by questionnaire and telephone interview. We prospectively recorded migraine attacks from a 12-month headache diary performed by a group of 62 women with a mean age of 36.0 years (range 16-46 years), who fulfilled the criteria of migraine without aura. Of these, 29 had MRM and 33 non-menstrual migraine. Mean ratio between number of attacks in the light arctic season (May-June-July) divided with total number of migraine attacks during 12 months was 0.24 (9.4/38.4) in the group of MRM compared with 0.25 (5.6/22.1) in others (confidence interval -4.2, 6.3, P = 0.84). Nor were there more migraine attacks in the dark season in an arctic area (November-December-January) in any group. We found a higher migraine attack rate in those with MRM, but no indication of more or less frequency of attacks during the bright arctic season. These findings support the assumption that MRM and seasonal variation of migraine are due to different mechanisms.