Table 1. DBS effects on non-motor symptoms as a whole and non-motor fluctuations in PD patients.

Author	Year	Outcome measure	Type of study	No. of patients	Main outcome after bilateral STN DBS
Dafsari et al.33	2016	Primary: NMS as a whole NMSS: 9 domains NMSQuest PDQ-8	Multicenter, open, 6-month prospective study	60	Overall NMSS improved, showing significant improvement in 4 domains: sleep/fatigue, perceptual problems/hallucinations, urinary and miscellaneous.
Wolz et al.24	2012	Primary: NMS as a whole Semi-structured questionnaire VAS	Cross-sectional study	34	No major immediate effects on frequencies, but improves severity of most NMS, particularly psychiatric symptoms (depression, anxiety, and fatigue).
Reich et al.21	2011	Primary: NMS as a whole NMSS	3–6 months prospective study	10	Shows holistic and selective beneficial effect on aspects of NMS. Especially on 5 particular domains: sleep, mood/cognition, urinary, sexual, and miscellaneous. Other domains show no change.
Nazzaro et al.22	2011	Primary: NMS as a whole NMSQuest, PDQ-39	1-year prospective study	24	NMS decreased significantly when assessed with a NMSQuest and significant improvement in QoL.
Zibetti et al.71	2007	Primary: NMS as a whole Clinical Interview	12–24 months prospective study	36	Ameliorates sleep and constipation.
Ortega-Cubero et al.27	2013	Primary: NMF Questionnaire	2-year prospective study	20	NMF severity and frequency related to the off-state were reduced.
Witjas et al. 26	2007	Primary: NMF Questionnaire	1-year prospective study	40	Alleviation of NMF seen, with significant positive effects on sensory, dysautonomic, and cognitive fluctuations. Less consistent in psychic response.

Abbreviations: DBS, deep brain stimulation; NMS, non-motor symptoms; NMF, non-motor fluctuations; NMSS, Non-Motor Symptoms Scale; NMSQuest, non-motor symptoms questionnaire; QoL, quality of life; PD, Parkinson’s disease; VAS, Visual Analog Scale; PDQ, Parkinson’s disease questionnaire.