Hypometric anticipatory postural adjustments in dystonia are not affected by deep brain stimulation of globus pallidus internus.

BACKGROUND: Dystonia is a movement disorder with patterned, directional, and often sustained muscle contractions that produce abnormal postures or repetitive movements. Deep brain stimulation (DBS) of the globus pallidus internus (GPi) is an effective and safe treatment for medically refractory dystonia. However, recent studies reported gait problems, gait freezing and falls in patients treated with DBS. Because these symptoms may point to deficient gait initiation processes, we systematically assessed the anticipatory postural adjustments (APAs) prior to stepping in dystonia patients with GPi-DBS. METHODS: Thirteen patients with focal/segmental dystonia under GPi-DBS and twelve healthy control subjects were included in the study. Data were collected using pressure sensitive sensors and APAs were studied by centre of pressure measures. We compared APAs of both groups and analysed the influence of GPi-DBS on APAs in patients. RESULTS: Medio-lateral and antero-posterior COP displacements, total COP path, maximal APA velocity and 1st step length were all smaller in patients for both ON (p=0.006, p=0.018, p=0.002, p=0.016, p=0.04) and OFF (p=0.001, p=0.01, p=0.001, p=0.03, p=0.024) condition compared to healthy subjects. GPi-DBS did not change APA parameters in patients. CONCLUSIONS: Observations that APAs are impaired in dystonia and are at the same time not affected by the stimulation current are compatible with the assumption that APAs and dystonic symptoms may rely on distinct networks, possibly within the same cortical and basal ganglia structures. With no effect of stimulation on APAs it is unlikely that this would be a mechanism of impaired balance in the patients after the surgery.

Postural stability under globus pallidus internus stimulation for dystonia.

OBJECTIVE: Deep brain stimulation of the globus pallidus internus (GPi-DBS) is an efficient and safe treatment for medically refractory dystonia. However, recent studies reported gait problems, falls and bradykinesia in patients after the DBS procedure. The aim of this study was to quantify the effect of GPi-DBS on postural performance in patients with cranio-cervical dystonia. METHODS: Thirteen patients with focal/segmental dystonia and GPi-DBS participated in the study. We performed two postural tests (pull test and push and release test) in on- and off-stimulation conditions and recorded the movements of the patients with inertial sensors. RESULTS: Under stimulation patients exhibited a higher number of steps (p=0.015), reduced first step length (p=0.011) and lower stepping velocity (p=0.001), compared to off stimulation. We observed a higher number of steps in the push and release test compared to the pull test (p=0.038). The interaction between stimulation condition and test type was significant (p=0.027). CONCLUSIONS: The velocity and amplitude of postural reactions are compromised by GPi-DBS in patients with cranio-cervical dystonia. SIGNIFICANCE: This information corresponds to patient's reports of falls and postural instability after GPi-DBS. Pre-operatively, patients should be informed about the possibility of the occurrence of such phenomena.