The somatic comorbidity of epilepsy: a weighty but often unrecognized burden

A range of medical and neurologic disorders occurs more frequently in people with epilepsy than in the general population and constitutes its somatic comorbidity. Common examples include cardiac, gastrointestinal, and respiratory disorders; stroke; dementia; and migraine. Alzheimer's disease and migraine are not only more common in epilepsy but are also risk factors for the development of seizures, suggesting a bidirectional association and shared disease mechanisms. Less well-appreciated associations with epilepsy include Parkinson's disease and obstructive sleep apnea. The association between epilepsy and other conditions can be due to a variety of interacting genetic, biologic, and environmental factors. We propose an etiologic classification of comorbidity into uncertain (coincidence or unknown), causal (cause), shared risk factors (common disease mechanisms or shared predisposing risk factors), and resultant (consequence). Co-occurrence of other conditions in a person with epilepsy can complicate diagnosis or have adverse prognostic implications. Management of these conditions may facilitate the treatment of epilepsy, as in the case of obstructive sleep apnea. The presence of somatic disorders in epilepsy is associated with increased health care needs, poorer health-related quality of life, and premature mortality. Prevention, identification, and adequate treatment of comorbid disorders in epilepsy should be an important part of epilepsy management at all levels of care.