Is lowering stimulation frequency a feasible option for subthalamic deep brain stimulation in Parkinson's disease patients with dysarthria?

Abstract Background The long-term effect of subthalamic nucleus deep brain stimulation (STN-DBS) on dysarthria can be detrimental. A transient beneficial effect of low-frequency stimulation (LFS) has been reported. Objective: to investigate if the magnitude of dysarthria could predict the effect of LFS on speech in STN-DBS PD patients and to verify whether the benefit is maintained over time. Methods a cohort study, comparing 10 PD patients with severe speech impairment (MDS-UPDRS item 3.1 ≥ 3) with 10 PD patients with mild speech impairment (MDS-UPDRS item 3.1 ≤ 2), all submitted to STN-DBS. Patients were tested in: MED OFF/STIM OFF, MED OFF/STIM ON (130 Hz, high frequency stimulation [HFS]), MED OFF/STIM ON (60 Hz - LFS) and MED ON with both HFS and LFS. The following was assessed in all conditions: voice (fundamental frequency and jitter), speech (articulatory diadochokinesis [DDK], pitch variability, rate and intelligibility) and motor performance (MDS-UPDRS-III). Results LFS compared to no stimulation and HFS, in the absence of l -dopa effect, significantly improved DDK and speech intelligibility for sentence, among patients with severe speech impairment. During the l -dopa effect, comparing LFS vs. HFS, there was a significant improvement of speech intelligibility in both groups. Five patients with severe speech impairment opted to maintain LFS. After six months, speech benefit was maintained but treatment adjustments were required. Conclusions LFS may offer both an immediate and long-lasting improvement of speech in a subgroup of STN-DBS patients with severe speech impairment during HFS. Nevertheless, its effect on motor symptoms may not be preserved over time.