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Abstract
The relation between depression and neurological disorders is generally construed as unidirectional and expressed as an increased risk of depression in the presence of a neurological disorder. In the past 15 years, however, data from several studies have suggested the existence of a bidirectional relation between depression and various neurological disorders, including dementia, epilepsy, stroke, and Parkinson's disease. This relation is expressed by an increased risk of occurrence or a worse prognosis of these disorders in individuals with a history of depression. For example, many studies have shown an increased prevalence of depression in patients with dementia. However, using data from a case-register study of almost 23 000 patients with an affective disorder, L Kessing and P Andersen suggested that the relation expressed as the number of major depressive episodes leading to an inpatient admission increased the risk of developing dementia.1 Thus patients with three admissions had close to a three-times increased rate of dementia (95% Cl 0.64-13.2), compared with patients with only one admission. In a separate study of 1003 elderly patients (all with a Mini Mental State score >26), the presence of significant depressive symptoms at baseline predicted a higher risk of cognitive decline 4 years later.2 Structural and functional neuroanatomical changes in primary major depressive disorders might help to explain these data.