The Effect of Short Pulse Width Settings on the Therapeutic Window in Subthalamic Nucleus Deep Brain Stimulation for Parkinson's disease

Background: Subthalamic nucleus deep brain stimulation (STN-DBS) is an established treatment for selected Parkinson's disease (PD) patients, but therapy is often limited by side effects. Previous studies indicate an inverse relationship of the therapeutic window (TW) to pulse width (PW) settings down to 60 mu s, but there is limited data available on the effect of shorter PWs. Objective: To define the TW of STN-DBS in PD at PW of 30 mu s (PW30) relative to standard PW settings at 60 mu s (PW60), and to compare speed of gait and speech intelligibility on the two PW conditions. Methods: Monopolar review data of 15 consecutive PD patients who had screening of contacts performed at PW60 and PW30 was used to calculate the TW at each contact. We compared the TWs of the most efficacious contact per STN, and a secondary analysis was performed comparing all contacts. Speed of gait with a timed 10 metre walk test, speech intelligibility, and perceptual characteristics of speech were also compared at the efficacy thresholds for PW60 and PW30. Results: The TW was significantly greater at PW30 [3.8 +/- 1.6mA] than at PW60 [1.7 +/- 1.1mA]. In the secondary analysis, 110 TWs could be calculated and these remained significantly higher at PW30. The timed 10 metre walk at PW30 was faster than at PW60, and perceptual rating scores of speech were significantly improved at PW30. Conclusions: STN-DBS in PD patients using a PW of 30 mu s significantly increases the TW compared to standard PW settings, and this effect is consistent across all contacts of an electrode. Speed of gait and perceptual speech scores are also improved at 30 mu s settings.