Impact of subthalamic nucleus deep brain stimulation on voice and speech in Parkinson’s disease

Subthalamic nucleus deep brain stimulation (STN-DBS) effectively alleviates motor symptoms in Parkinson’s disease (PD), yet its impact on speech and voice remains inconsistent. This study examined acoustic parameters, perceptual features, and speech intelligibility using a large, methodologically standardized cohort. A total of 105 PD patients (55 females, 50 males; mean age ≈ 57 years) undergoing STN-DBS were evaluated. All received posterolateral electrode placement, bilateral stimulation, and a postoperative 30–35% reduction in levodopa. Acoustic measures fundamental frequency (F0), jitter, shimmer, harmonic-to-noise ratio (HNR), and maximum phonation time (MPT) were obtained one day preoperatively and at three months postoperatively. Perceptual ratings (GRBAS), Voice Handicap Index-10 (VHI-10), and speech intelligibility (percentage of correctly produced words) were assessed concurrently. Motor symptoms improved in the medication-on state (19.4 → 13.6). Acoustic analysis showed no significant postoperative change in F0, shimmer, HNR, or MPT; however, jitter improved significantly in both sexes. On the GRBAS scale, all parameters improved in females, whereas grade, roughness, and asthenia improved in males. VHI-10 scores improved overall (22.7 → 21.8; p = 0.031), driven primarily by females (27.5 → 25.9; p = 0.004). Speech intelligibility increased in the full cohort (70.1% → 71.7%; p = 0.01) and reached significance in females but not males. Higher age and greater motor severity correlated with reduced intelligibility, while sex, PD subtype, and stimulation parameters showed no associations. STN-DBS yields short-term motor improvement and produces parameter-specific speech effects. Utilizing a highly standardized “pure” cohort enhances interpretability and suggests that, under controlled conditions, STN-DBS can exert a beneficial influence on speech performance despite its multifactorial impact.