Investigation of DBS Effects (Washout and Washin) on Parkinsonian Speech
Deep brain stimulation (DBS) is a neurosurgical intervention that reduces some parkinsonian motor symptom severity, but its effect on parkinsonian speech is not as consistent nor reliable. Both STN/GPi DBS can impair certain modalities of parkinsonian speech reducing activities of daily living dependent on intelligible and dynamic speech. The added speech impairments under STN/GPi DBS can result in further social isolation and a worsening of one’s mental health as the capability to verbally communicate is lost over time. As demonstrated with other axial symptoms of PD, speech is slow to respond to DBS intervention. Investigating how stimulation alters PD speech dynamics over time may be beneficial in limiting negative DBS effects. A group of 16 patients diagnosed with idiopathic Parkinson’s disease completed an oral diadochokinetic assessment (DDK) as the DBS effect was lost (Washout) or gained (Washin) over time. The speech assessment yielded mixed results with DBS Washout and DBS Washin modulating certain aspects of PD speech differently. No real DBS effect was captured by the phonation metrics (Pitch and Intensity); however, a real DBS effect was captured by the articulation metrics Repetition Count and Bout Duration. Repetition Count and Bout Duration show promise as reliable metrics that captured a true DBS effect altering parkinsonian speech. Both metrics may be useful in future speech assessments involving STN DBS or GPi DBS. Future investigations quantifying the rate at which a DBS effect alters specific components of PD speech are necessary to try and reduce potentially negative speech outcomes under DBS stimulation.