[Dementia and bipolar disorder on the borderline of old age]

Dementia and bipolar disorder have been traditionally considered two separate clinical entities. However, recent preclinical and clinical data in elderly people suggest that they are in fact related. Several theories have been put forward to interpret their relationship which could be summed up as follows: (1) Dementia could increase the risk for the emergence of bipolar symptoms, or (2) conversely, bipolar disorder might be associated with heightened risk for developing pseudodementia or dementia. (3) Alternatively, dementia, other brain diseases or drugs affecting brain function could lead to the combination of symptoms of dementia and bipolar disorder in elderly individuals. The two disorders demonstrate similarities with respect to their clinical expression (agitation, psychotic, mood and cognitive symptoms) and structural brain neuroimaging (enlarged lateral ventricles and white matter hyperintensities using magnetic resonance imaging-MRI). Despite the above similarities, the two disorders also have important differences. As expected, cognitive symptoms prevail in dementia and mood symptoms in bipolar disorder. In dementia but not in bipolar disorder there is evidence that brain structural abnormalities are diffuse and hippocampal volumes are smaller. Dementia and bipolar disorder present different abnormalities in functional brain neuroimaging. The pattern of "ventral" hyperactivity and "dorsal" hypoactivity in brain emotional circuits at rest is revealed in bipolar disorder but not dementia. With respect to their treatment, acetylcholinesterase inhibitors and memantine are indicated against cognitive symptoms in dementia and also improve behavioural and psychological symptoms appearing during the course of dementia. Lithium, anticonvulsants, antipsychotics and antidepressants are effective in the management of the acute episodes of bipolar disorder of younger adults, but there are not yet evidence-based data in elderly bipolar patients. It is likely that the efficacy of anticonvulsants and antipsychotics is superior during acute bipolar episodes in elderly individuals, although both drug categories have been associated with important adverse effects. Current data suggest that the best option during the maintenance phase of the elderly bipolar disorder is the continuation of agents which have been shown effective in the management of acute episodes. The appropriate treatment of cognitive symptoms in elderly bipolar patients has not been thoroughly investigated. In addition, the therapeutic value of psychotropics except cholinesterase inhibitors and memantine in dementia is still controversial, due to their association with side effects. Recent studies which have focused on the role of lithium in dementia could help clarify the relationship of dementia and elderly bipolar disorder. Although there are promising findings with respect to the value of lithium treatment in the prevention of dementia, the existing clinical studies do not support any beneficial effect of lithium administration on enhancing cognitive functioning of people with dementia. The specific role of lithium in dementia and the preventive value of interventions against vascular risk factors in both disorders remain to be evaluated in future prospective studies.