Background The prevalence and clinical features associated with bipolar disorders (BDs)–migraine comorbidity have been reported inconsistently across different studies, therefore warranting a systematic review on the matter. Methods A systematic review was conducted in accordance with the PRISMA statement searching major electronic databases for documents indexed between January, 2000 and July, 2014. Eligible studies were those including quantitative data on prevalence rates and clinical features associated to BD–migraine comorbidity; case reports excluded. Three authors independently conducted searches, quality assessment of the studies and data extraction. Results Several cross-sectional studies, and a handful of retrospective follow-up studies or non-systematic reviews assessed the prevalence and/or the clinical correlates of migraine–BD comorbidity. High prevalence rates and a significant burden of BD–migraine comorbidity were common findings, particularly in case of BD-II women (point-prevalence rates up to 77%), migraine with aura (up to 53%) and/or cyclothymic temperament (up to 45% of the cases). Limitations Some of the biases encountered in a few studies accounted by the present review may nonetheless have hampered the generalizability of the overall conclusions drawn herein. Conclusions BD–migraine comorbidity may comprise of a sub-phenotype of BDs requiring patient-tailored therapeutic interventions to achieve an optimal outcome. Specifically, additional studies including longitudinal follow-up studies are aimed in order to shed further light on the actual prevalence rates and clinical features associated to BD–migraine comorbidity, with a special emphasis towards the clinically suggestive potential connection between mixed features, bipolar depression, migraine, and increased risk for suicidality. PROSPERO registration number: CRD42014009335.
