The effect of serotonin reuptake and serotonin-noradrenaline reuptake inhibitors on motor symptoms in Parkinson's disease: A PPMI-based matched-subject study

<b>Background:</b> Depression often co-occurs with Parkinson's disease (PD) and is effectively treated with selective serotonin reuptake inhibitors (SSRI) and serotonin and noradrenaline reuptake inhibitors (SNRI), but their effect on motor symptoms has not yet been conclusively demonstrated. <b>Objective:</b> To assess the impact of the SSRI/SNRI on the motor symptoms of PD. <b>Methods:</b> We used data from the Parkinson's Progression Markers Initiative database, in a matched subject design with a target group (N = 47) which had been taking SSRI/SNRI medication and a control group (N = 90) which had not. Matching criteria included Movement Disorders Society Unified Parkinson's Disease Rating Scale part III (MDS-UPDRS-III) total score and its subscales' scores, and levodopa equivalent daily dose (LEDD) at the time of the first examination (initial LEDD). For the target group, we compared the MDS-UPDRS-III score before and after taking the SSRI/SNRI medication, while for the control group we compared two equally spaced examinations. <b>Results:</b> In the target group, we found a greater worsening of motor scores, which was associated with lower values of initial LEDD. In addition, apathy was an independent predictor of motor worsening. <b>Conclusions:</b> SSRI/SNRI-use seems to be characterized by a steeper worsening of motor symptoms, which can be predicted by a lower initial LEDD. Further research should continue to investigate the effect of SSRI/SNRI-use on motor symptoms in PD.