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

Abstract

Parkinson’s disease (PD) can produce postural abnormalities of the standing body position such as kyphosis. We investigated the effects of PD, deep brain stimulation (DBS) in the subthalamic nucleus (STN), vision and adaptation on body position in a well-defined group of patients with PD in quiet standing and during balance perturbations. Ten patients with PD and 25 young and 17 old control participants were recruited. Body position was measured with 3D motion tracking of the ankle, knee, hip, shoulder and head. By taking the ankle as reference, we mapped the position of the joints during quiet standing and balance perturbations through repeated calf muscle vibration. We did this to explore the effect of PD, DBS in the STN, and vision on the motor learning process of adaptation in response to the repeated stimulus. We found that patients with PD adopt a different body position with DBS ON vs. DBS OFF, to young and old controls, and with eyes open vs. eyes closed. There was an altered body position in PD with greater flexion of the head, shoulder and knee (p≤0.042) and a posterior position of the hip with DBS OFF (p≤0.014). With DBS ON, body position was brought more in line with the position taken by control participants but there was still evidence of greater flexion at the head, shoulder and knee. The amplitude of movement during the vibration period decreased in controls at all measured sites with eyes open and closed (except at the head in old controls with eyes open) showing adaptation which contrasted the weaker adaptive responses in patients with PD. Our findings suggest that alterations of posture and greater forward leaning with repeated calf vibration, are independent from reduced movement amplitude changes. DBS in the STN can significantly improve body position in PD although the effects are not completely reversed. Patients with PD maintain adaptive capabilities by leaning further forward and reducing movement amplitude despite their kyphotic posture.

Anticipatory Postural Adjustments and Compensatory Postural Responses to Multidirectional Perturbations—Effects of Medication and Subthalamic Nucleus Deep Brain Stimulation in Parkinson’s Disease

“…Switching DBS on increased coupling between segments, including the ankles, which may have simplified the corrective postural responses and consequently have caused the earlier and more pronounced activation of lower leg muscles [ 75 ]. This is supported by several other studies that found that STN-DBS alters postural alignment and consequently can effect postural reflex responses [ 71 , 76 , 105 ]. Studies investigating the latency of electrically induced so-called Hofmann (H) reflex, which is an analogue of the mechanically induced stretch reflex, also provide evidence that STN-DBS may change reflex timing [ 156 , 157 , 158 ].…”

“…Those results might be explained in part by the interference of other early parkinsonian motor symptoms, like rigidity and bradykinesia, which are associated with hypertonic muscle contraction and increased background muscle activity [ 63 , 65 , 102 , 103 , 104 ]. Although there were no obvious signs of significant posture deformities in our patient cohorts, stooped parkinsonian posture with slightly flexed knees and a flexed trunk may have increased background muscle activity as well [ 76 , 91 , 105 , 106 ]. Increased background muscle activity, in turn, increases the co-contraction of agonistic and antagonistic ankle muscles and therefore leads to joint stiffness [ 65 , 66 , 67 ].…”

“…Nevertheless, study results regarding the effect of STN-DBS on CPR are controversial. Studies that found beneficial effects of the former comparing DBS in the “off state” with DBS in the “on” state reported enhanced postural strategies, improved body position, and increased agonist muscle burst durations during balance perturbations [ 75 , 76 , 78 ]. Using rather subjective clinical balance tests, Li et al reported positive effects on postural instability after DBS surgery, which were still noticeable after 12 months [ 81 ].…”

“…Studies investigating postural instability, comparing it between when DBS was on vs. off and pre vs. post DBS surgery, presented inconsistent results. Turning DBS on revealed immediate improvements in postural flexibility, including enhanced coupling between segmental movements of the body and normalized agonistic contractions during computerized balance perturbations [ 75 , 76 , 77 , 78 ]. In addition, comparing postural performance before vs. several months after DBS surgery showed better postural performance and reduced the number of falls [ 35 , 78 ].…”

Reduced Range of Gait Speed: A Parkinson’s Disease-Specific Symptom?

“…Changes of such adaptabilities due to, e.g., aging have already been shown for many pro-49 cesses [14], including immune response [15], stem cell development [16], and the locomotor system performance in general [17,18]. As persons with Parkinson's disease (PwPD) show reduced adaptability at different levels (e.g., weaker adaptive responses to balance perturbations during quiet standing [19] or freezing of gait when gait needs to be adapted to external requirements [20]), we hypothesized that PD may specifically lead to reduced RGS.…”