The effects of neurosurgical treatments on motor speech function in Parkinson's disease

In recent years, there has been a resurgence in the use of neurosurgicalntreatments to alleviate motor disturbances in Parkinson's Disease (PD). Despite thenincreased use of neurosurgical treatments, minimal research into the effects of thesenprocedures on motor speech function in PD has been reported. Previously, it wasnassumed that motor speech function may improve following post-operativenimprovements in limb motor symptoms. The primary aim of the current thesis was tonexamine the effects of pallidotomy, thalamotomy, and deep brain stimulation (DBS) onnperceptual, acoustic, and physiological speech parameters in a group of individuals withnPD.nnnnnn Twenty-two individuals with idiopathic PD who were treated with stereotacticnneurosurgical procedures (surgical PD participants) participated in the study. Thenspeech function of the 22 surgical PD (SPD) participants was assessed pre-surgery andnthree months post-surgery. In addition, the SPD participants' results were compared to angroup of 25 normal control participants (NC group) matched for age and sex. Thencurrent thesis also collected data from a comparison group of 16 'non-surgical PD'nparticipants (NSPD participants) who had not undergone surgical intervention. ThenNSPD group was included to control for the influence of disease progression on the pre-postnsurgical measures in the SPD participants.nnnnnn The speech function of the SPD, NSPD, and NC participants was assessed usingna perceptual speech analysis (FitzGerald, Murdoch, a Chenery, 1987), the FrenchaynDysarthria Assessment (Enderby, 1983), and the Assessment of Intelligibility of Dysarthric Speech (ASSIDS; Yorkston a Beukelman, 1984). Although the SPDngroup's general motor ratings revealed a significant post-operative improvement innoverall motor performance, perceptual speech findings indicated that neurosurgicalnintervention did not systematically change the SPD participants' speech production.nnnnnn To determine the effects of pallidotomy on motor speech function, thenrespiratory, laryngeal, velopharyngeal, and articulatory subsystems were subsequentlynevaluated in a series of three studies examining speech function pre- surgery and 3nmonths post-surgery. The assessment of respiratory function, utilising kinematic andnspirometric techniques revealed that the participants who underwent pallidotomyn(pallidotomy PD group) had essentially the same breath patterning for speech as thencontrol participants. Furthermore, there was no significant change observed in thenpallidotomy PD (PPD) group's speech breathing patterns and respiratory-phonatoryncontrol following pallidotomy.nnnnnn The results of the electroglottographic and aerodynamic assessment of laryngealnfunction failed to identify a significant change in the PPD group's phonatory functionnfollowing surgery. Similarly, acoustic parameters of sound pressure level and voicenquality did not reveal significant change following surgery. In addition, the PPD group'snvelopharyngeal function was assessed using the Nasometer (Kay Elemetrics) whilenarticulatory function was assessed using lip and tongue pressure transduction systems.nThe PPD group's nasalance and lip function parameters revealed that there were nonsignificant changes in these two aspects of speech production following pallidotomy.nFurthermore, the physiological tongue measures generally recorded no significantnchanges, although there was a post-operative improvement in tongue fine force controlnthat occurred within the normal range.nnnnnn The current thesis also examined the motor speech profile of 4 PD participantsnwho underwent left ventrolateral thalamotomy. The results demonstrated that leftnthalamotomy had a minimal impact on the thalamotomy PD (TPD) participants'nfunctional speech production, while one TPD participant recorded a post-operativendecline in lingual function. An investigation of another 4 PD participants who hadnundergone DBS comprised the final investigation of this thesis. Results suggested thatnDBS in these four cases failed to effect functional change in the DBS participants'nspeech production despite improvements in limb motor symptoms.nnnnnn The current research revealed that neurosurgical treatments resulted inndifferential effects on limb and speech motor impairments in a cohort of PD participantsnwith relatively mild pre-operative dysarthria. The findings were discussed with respectnto the heterogeneous nature of PD and differences between speech and limb motornfunction. Future directions for research include the examination of larger cohorts ofnmoderate to severely dysarthric individuals with PD and further exploration of thensomatotopic organization of the basal ganglia circuitry with respect to speech functionnn