Investigating susceptibility to bipolar disorder, migraine and epilepsy

Epidemiological and clinical studies demonstrate a high degree of comorbidity between bipolar disorder (BD) and migraine. A relationship between BD and epilepsy is also suggested, with both disorders displaying phenotypically similar symptom profiles. The overall aim of this thesis was to further explore the relationship between BD and the neurological conditions of migraine, and epilepsy, within a large, well-characterised sample of individuals with BD. Data were utilised from the Bipolar Disorder Research Network (BDRN); a large (n>6000) UK sample of individuals with a diagnosis of BD. Lifetime history of migraine and epilepsy were assessed within BDRN using questionnaire and telephone interview methods. Migraine was highly prevalent within the bipolar sample and was found to disproportionately affect those with bipolar II disorder. Bipolar subjects with comorbid migraine experienced a relatively distinct illness profile, with a multivariate model revealing migraine comorbidity to be characterised by an increased risk of suicide attempt and anxiety disorder. Further analysis of the migraine phenotype revealed that observed differences in the clinical presentation of BD associated with migraine were largely associated with the migraine with aura subtype. A high rate of self-reported epilepsy was identified within the bipolar sample and group differences were revealed in the clinical course of the bipolar illness according to the presence of self-reported epilepsy. Multivariate analysis revealed an independent association of a history of suicide attempt with self-reported epilepsy within BD. Findings from this thesis highlight the importance of identifying migraine and epilepsy within BD, and that their recognition and treatment may have a beneficial impact on the course of illness and outcome in BD. This thesis also suggests that these comorbidities may represent a clinically useful subgroup characterised by specific clinical features, and may provide an opportunity for subcategorising for future aetiological studies, potentially facilitating the identification of shared pathophysiological mechanisms