Trigger factors and premonitory features of migraine attacks: summary of studies.

OBJECTIVE: In this second of a 2-part series, we review the available literature on trigger factors and premonitory features in migraine. BACKGROUND: In the absence of biological markers of preceding attacks of migraine, trigger factors and premonitory symptoms are valuable though methodologically challenging phenomena to study. DESIGN/METHODS: We focus on selected studies of retrospective surveys, diary studies, and clinical trials. We review the heterogeneity of selected studies and their conclusions performed to date and highlight that prospective electronic diary studies provide most reliable information that can be used for future development of preemptive therapy. CONCLUSION: We conclude that trigger factors and premonitory symptoms are very common, but that the frequency estimates vary widely based on the study approach and population. We recommend that multimodal approaches are necessary for the comprehensive study of predictive biophenotypes as determined by triggers and premonitory symptoms, including retrospective and prospective cohort studies and case-crossover studies.