Objective: To investigate the temporal relationships between a range of neurological diseases and affective disorders.
Method: Data derived from linkage of the Danish Psychiatric Central Register and the Danish National Hospital Register. Seven cohorts with neurological index diagnoses and two control group diagnoses were followed for up to 21 years. The incidences of affective disorders in the different groups were compared with the control groups, using competing risks to consider the risk of affective disorder and the risk of death in the same analysis.
Results: We found an increased incidence of affective disorders in dementia, Parkinson's disease, epilepsy, stroke and intracerebral haemorrhage compared with control groups. The association was found to be the strongest for dementia and Parkinson's disease. In hospitalized patients, with incident multiple sclerosis, the incidence of affective disorder was lower than the incidence in the control groups.
Conclusion: In neurological diseases there seems to be an increased incidence of affective disorders. The elevated incidence was found to be particularly high for dementia and Parkinson's disease (neurodegenerative diseases).