Effects of different electrical parameter settings on the intelligibility of speech in patients with Parkinson's disease treated with subthalamic deep brain stimulation.

We evaluated the effects of different electrical parameter settings on the intelligibility of speech in patients with Parkinson's disease (PD) bilaterally treated with deep brain stimulation (DBS) in the subthalamic nucleus (STN). Ten patients treated with DBS for 15 +/- 5 months (mean, SD) with significant (P < 0.01) symptom reduction (Unified Parkinson's Disease Rating Scale III) were included. In the medication off condition, video laryngostroboscopy was performed and then, in random order, 1 1 DBS parameter settings were tested. Amplitude was increased and decreased by 25%, frequency was varied in the range 70 to 185 pps, and each of the contacts was tested separately as a cathode. The patients read a standard running text and five nonsense sentences per setting. A listener panel transcribed the nonsense sentences as perceived and valued the quality of speech on a visual analogue scale. With the patients' normally used settings, there was no significant (P = 0.058) group difference between DBS OFF and ON, but in four patients the intelligibility deteriorated with DBS ON. The higher frequencies or increased amplitude caused significant (P < 0.02) impairments of intelligibility, whereas changing the polarity between the separate contacts did not. The settings of amplitude and frequency have a major influence on the intelligibility of speech, emphasizing the importance of meticulous parameter adjustments when programming DBS to minimize side effects related to speech.