Epilepsy and migraine as comorbid disorders: Epidemiologic perspectives

Comorbidity is defined as the co-occurrence of 2 medical conditions more frequently than would be expected by chance alone. Migraine and epilepsy are highly comorbid and share clinical features that suggest overlapping pathophysiology. The Epilepsy Family Study of Columbia University demonstrates the comorbidity of migraine and epilepsy; this relationship cannot be explained by a unidirectional causality (ie, that one disorder causes the other), shared genetic risk factors, or shared environmental risk factors. Analysis of epidemiologic and biological data suggests that brain hyperexcitability due either to environmental or genetic risk factors may account for the co-occurrence of migraine and epilepsy. However, our current understanding of hyperexcitability is not yet clear. Comorbidity is critical because it affects diagnosis as well as treatment. When conditions are comorbid, it is a mistake to make a single diagnosis. When epilepsy is diagnosed, it is more likely, not less likely, that the patient also has migraine. The presence of comorbid disorders presents both therapeutic opportunities and limitations. In some cases, a single medication can be used to treat both disorders; in other cases, medication to treat one disorder may be contraindicated for the other disorder.