Effects of subthalamic stimulation on speech of consecutive patients with Parkinson disease

Abstract

Objective: Subthalamic nucleus deep brain stimulation (STN-DBS) is an effective treatment for advanced Parkinson disease (PD). Following STN-DBS, speech intelligibility can deteriorate, limiting its beneficial effect. Here we prospectively examined the short- and long-term speech response to STN-DBS in a consecutive series of patients to identify clinical and surgical factors associated with speech change.

Methods: Thirty-two consecutive patients were assessed before surgery, then 1 month, 6 months, and 1 year after STN-DBS in 4 conditions on- and off-medication with on- and off-stimulation using established and validated speech and movement scales. Fifteen of these patients were followed up for 3 years. A control group of 12 patients with PD were followed up for 1 year.

Results: Within the surgical group, speech intelligibility significantly deteriorated by an average of 14.2%±20.15% off-medication and 16.9%±21.8% on-medication 1 year after STN-DBS. The medical group deteriorated by 3.6%±5.5% and 4.5%±8.8%, respectively. Seven patients showed speech amelioration after surgery. Loudness increased significantly in all tasks with stimulation. A less severe preoperative on-medication motor score was associated with a more favorable speech response to STN-DBS after 1 year. Medially located electrodes on the left STN were associated with a significantly higher risk of speech deterioration than electrodes within the nucleus. There was a strong relationship between high voltage in the left electrode and poor speech outcome at 1 year.

Conclusion: The effect of STN-DBS on speech is variable and multifactorial, with most patients exhibiting decline of speech intelligibility. Both medical and surgical issues contribute to deterioration of speech in STN-DBS patients.

Classification of evidence: This study provides Class III evidence that STN-DBS for PD results in deterioration in speech intelligibility in all combinations of medication and stimulation states at 1 month, 6 months, and 1 year compared to baseline and to control subjects treated with best medical therapy.

Figure 1. Location of the active contacts at 1 year post bilateral subthalamic nucleus deep brain stimulation (STN-DBS)

Location of the active contacts in 31 patients at 1 year post bilateral STN-DBS as transposed onto the Schaltenbrand atlas adopting the radiologic imaging convention (right STN on the left side of the image). Top: coronal view adapted from plate 27, f.p. 3.0. Contacts related to the superior (A) and inferior (E) segment of the STN are shown. The middle section of the STN in coronal view is further subdivided into 3 segments in the axial plane shown below. Therefore, the coronal and axial views show different contacts. Bottom: axial view adapted from plate 55, H.v. 4.5. Contact location is shown in relation to the anteromedial (B), central (C), and posterolateral (D) segments of the STN. Selected abbreviations: Ru = red nucleus; Sth = subthalamic nucleus; Z.i. = zona incerta. (Scaltenbrand G, Wahren W. Atlas for Stereotaxy of the Human Brain, 2nd ed. New York: Thieme; 1977. Plates 27;55. Reprinted by permission.)

Figure 2. Speech intelligibility at 3 years

Speech intelligibility (% of words understood) for the surgical group (n = 15) at baseline, 1 month, 6 months, 1 year, and 3 years post bilateral subthalamic nucleus deep brain stimulation (on-stimulation) (mean ± SEM).