Exploring the effects of deep brain stimulation and vision on tremor in Parkinson’s disease - benefits from objective methods

Abstract

Background: Tremor is a cardinal symptom of Parkinson's disease (PD) that may cause severe disability. As such, objective methods to determine the exact characteristics of the tremor may improve the evaluation of therapy. This methodology study aims to validate the utility of two objective technical methods of recording Parkinsonian tremor and evaluate their ability to determine the effects of Deep Brain Stimulation (DBS) of the subthalamic nucleus and of vision. Methods: We studied 10 patients with idiopathic PD, who were responsive to L-Dopa and had more than 1 year use of bilateral subthalamic nucleus stimulation. The patients did not have to display visible tremor to be included in the study. Tremor was recorded with two objective methods, a force platform and a 3 dimensional (3D) motion capture system that tracked movements in four key proximal sections of the body (knee, hip, shoulder and head). They were assessed after an overnight withdrawal of anti-PD medications with DBS ON and OFF and with eyes open and closed during unperturbed and perturbed stance with randomized calf vibration, using a randomized test order design. Results: Tremor was detected with the Unified Parkinson's Disease Rating Scale (UPDRS) in 6 of 10 patients but only distally (hands and feet) with DBS OFF. With the force platform and the 3D motion capture system, tremor was detected in 6 of 10 and 7 of 10 patients respectively, mostly in DBS OFF but also with DBS ON in some patients. The 3D motion capture system revealed that more than one body section was usually affected by tremor and that the tremor amplitude was non-uniform, but the frequency almost identical, across sites. DBS reduced tremor amplitude non-uniformly across the body. Visual input mostly reduced tremor amplitude with DBS ON. Conclusions: Technical recording methods offer objective and sensitive detection of tremor that provide detailed characteristics such as peak amplitude, frequency and distribution pattern, and thus, provide information that can guide the optimization of treatments. Both methods detected the effects of DBS and visual input but the 3D motion system was more versatile in that it could detail the presence and properties of tremor at individual body sections.

Spectral analysis of body movement during deep brain stimulation in Parkinson’s disease

“…A significantly altered spectral power distribution across body segments and a reduction of spectral power in the lateral direction at the head and shoulders indicated an altered postural strategy with DBS ON. A decrease in tremor is a well-known effect of DBS STN and is consistent with the findings of reduced spectral power >4Hz [2,[17][18][19][20]. In a review, Gross and Lozano [21] noted a 45-97% decrease in tremor amplitude from DBS, levels also confirmed by a more recent study [2].…”

“…Tremor is approximately sinusoidal and has a relatively fixed frequency across the body [1], though its amplitude and shape can vary [2,3]. For example, spectral analysis of movement in patients with Parkinson's resting tremor has shown it to have a frequency of between 4 to 7Hz that varies in amplitude between individuals [4].…”

“…Thus, any tremor-generating signal and its treatment are likely to affect different parts of a complex subcortical network. Little consideration has been given to frequency and amplitude variations in Parkinsonian resting tremor during stance [2] where a suitable measure is the total power content across a broad spectrum [5,6].…”

Deep brain stimulation in the subthalamic nuclei alters postural alignment and adaptation in Parkinson’s disease

“…The final PD group had 10 adults (9 men and 1 woman) aged between 59 and 69 years (mean age 64.3 years, SEM 1.3 years; mean height 1.77m, SEM 0.02m; and mean weight 79.6 kg, SEM 2.7kg). The clinical details, such as settings of the DBS devices, medication, UPDRS scores and description of the neurosurgical procedures can be found in Table 1 and in previous articles [17,[24][25][26].…”

Strategic alterations of posture are delayed in Parkinson’s disease patients during deep brain stimulation

“…However, a worsening tremor is associated with poor quality of life and disability 2 . Although PD is associated with a severe depletion of dopaminergic neurons in the nigrostriatal pathway of the basal ganglia, deep brain stimulation (DBS) of the subthalamic nucleus (STN) produces significant reductions of tremor amplitude, although the exact mechanism is not known 3 , 4 . Several possible routes of action have been considered including the excitation and inhibition of neural circuits in and around the basal ganglia, extending to larger circuits with time 5 .…”