We previously reported that Parkinson's disease (PD) patients treated with subthalamic nucleus deep brain stimulation (STN-DBS) had distinct phenotypes of speech and voice disorders: hypokinetic dysarthria, stuttering, breathy voice, strained voice, and spastic dysarthria. However, changes over time remain unclear. In the present study, 32 consecutive PD patients were assessed before and up to 1 year after surgery (PD-DBS). Eleven medically treated PD patients were also assessed (PD-Med). Speech, voice, motor, and cognitive functions were evaluated. At baseline, the incidence of hypokinetic dysarthria (63% of PD-DBS vs. 82% of PD-Med), stuttering (50% vs. 45%), breathy voice (66% vs. 73%), and strained voice (3% vs. 9%) was similar between groups. At 1 year, a slight but significant deterioration in speech intelligibility (p < 0.001) and grade of dysphonia (p = 0.001) were observed only in PD-DBS group compared with baseline. During the follow-up, stuttering (9% vs. 18%) and breathy voice (13% vs. 9%) emerged in PD-DBS and PD-Med, but strained voice (28%) and spastic dysarthria (44%) emerged only in PD-DBS. After the stimulation was stopped, strained voice and spastic dysarthria improved in most patients, while stuttering and breathy voice improved in a minority of patients. These findings indicate that the most common DBS-induced speech and voice disorders are strained voice and spastic dysarthria and that STN-DBS potentially aggravates stuttering and breathy voice. An improved understanding of these types of disorders may help detect speech and voice deteriorations during the early phase and lead to appropriate treatments.
Keywords: Deep brain stimulation; Parkinson’s disease; Speech disorders; Subthalamic nucleus; Voice disorders.