Risk factors for depression in community treated epilepsy

© 2013 Dr. Cameron J. LaceyRisk factors for depression in people with epilepsy remain elusive despite longstanding research into this prevalent, serious comorbidity. In part, this stems from the dominance of samples from tertiary care settings, subjects unrepresentative of the general population of people with epilepsy. This has changed recently with the advent of community-based studies, of which the present study is an example. This thesis investigated the association between depression and epilepsy, applying findings from general depression research to the aetiology of depression in people with epilepsy. The research question was addressed in several ways. A systematic review of risk factors for depression in community epilepsy studies found that the most consistent factors were socio-demographic, despite most studies focusing on epilepsy-related factors. Psychological factors implicated in depression were rarely studied although, in the few studies that did, associations with depression were consistently observed. Second, using data from an existing sample of community-treated people with epilepsy (the Tasmania Epilepsy Register, TER), a first study investigated the prevalence of and risk factors for ‘psychological distress’ (principally anxiety and depression) and its associations with health service use. Psychological distress was common but available variables explained little variance, reflecting that TER was not designed specifically to investigate psychiatric comorbidity. However, ‘psychological distress’ was associated with greater use of primary health care, a useful reminder for clinicians that more frequent attendance for medical care by people with epilepsy may indicate psychiatric comorbidity more than seizure activity. Third, a second study, designed to more comprehensively investigate risk factors for depression, utilised the best-established psychosocial and neurological factors from the literature, as well as a specific, important polymorphism affecting the serotonin transporter gene (SLC6A4). The TER Mood Study recruited subjects from the Register, employing a mailed questionnaire, and saliva collection for genetic study. A large sample (n=554) was recruited and was representative of community treated epilepsy subjects. Depression was associated with increased seizure frequency, stressful life events, a past history of depression, neuroticism, lower social support and use of gabapentin. The model explained 64% of the variance of depression, the best available model to date. While most risk factors for depression identified in this sample of people with epilepsy were similar to those seen in other samples, negative findings for gender and socioeconomic status suggest that there may be several pathways to depression in patients with epilepsy. This is the first study to test in epilepsy subjects the hypothesis of an interaction of life stress and the SLC6A4 polymorphism as a moderator of depression risk. The data did not support the hypothesis. However, strong associations were observed between depression and stressful life events and a lack of associations with indices of disease severity. This has implications for chronic disease depression research generally, not only epilepsy, as many studies have not measured general life stress, only stress narrowly attributable to chronic disease itself. This work has epidemiological, clinical and health services implications and gives guidance to future research into risk factors for depression in epilepsy and other chronic illnesses