Affect in Parkinson's disease: validation of the two-factor approach

Depression in Idiopathic Parkinson's disease (IPD) is frequent, difficult to recognize, under managed and has a profound impact on quality of life. Current categorization of diagnosis in psychiatry poorly applies to the protean manifestations of mood disorders presented by parkinsonian patients. In this study we have chosen to dissect the state of depressive mood as assessed with the Beck Depression Inventory (BDI) at different points in time of pharmacological interventions using a dimensional approach. The 21 items of the BDI were classified in two new categories or factors: hyperkinetic and hypokinetic. The hyperkinetic factor included all items related to unbalanced intrusions of negative feelings and ideas, as well as to behavioral hyperactivity. The hypokinetic factor included all items related to loss of drive for appetitive behaviors and loss of mental and physical energy. The objectives were to (1) compare different pharmacological treatments on the two-factor approach in PD depression, (2) determine the influence of levodopa therapy on the two-factor approach, and (3) explore the two-factor approach in placebo conditions. Three sets of analyses using the hypo/hyperkinetic dichotomy favour a neurobiological dissociation of these factors in response to pharmacological intervention: symptoms of the hyperkinetic factor are responsive to serotonergic drugs while those of the hypokinetic one are not and may even show deterioration under SSRIs. In contrast, the hypokinetic factor is responsive to dopaminergic drugs and may show deterioration under serotonergic drugs. Furthermore, the two factors seem to transiently dissociate on placebo intervention aiming at correcting either mood or motor status. The dimensional approach to depression symptomatology may thus be of heuristic value in probing aminergic modulation of mood in IPD and establishing new correlations between affective and motor symptoms.