Added value of the instrumented Timed-Up and Go test (iTUG) in the long-term assessment of PD patients with bilateral subthalamic nucleus deep brain stimulation (STN-DBS)

Abstract

STN-DBS is an effective long-term treatment in PD, improving a broad spectrum of symptoms, including tremor, rigidity, and bradykinesia (Fig. 1a) together with dopaminergic treatment. Among axial symptoms, gait disorders are common in PD. This study examines the long-term effects of different combinations of these two treatments in a cohort of advanced PD patients by means of the iTUG. Observational study on consecutive PD patients previously treated with bilateral STN-DBS. Disease severity was assessed using the UPDRS part III. Accelerometric data were acquired using an inertial sensor (G-WALK, BTS Bioengineering). Three iTUG trials were recorded in each of four stimulation and drug conditions: on-stimulation/off-medication, off-stimulation/off-medication, on-stimulation/on- medication and while preforming a cognitive task (counting backward, DUAL TASK) with both stimulation and medication on. Data were segmented into six phases (e.g., rising from chair, walking) as in [1]. A set of indices was computed including durations, RMS amplitudes, peak accelerations, peak angular velocities, indices of symmetry (improved Harmonic Ratio) and smoothness (Spectral Arc) [1]. A one-way non-parametric ANOVA was carried out, with the condition as a factor, followed by paired comparisons when appropriated. Statistical significance was set at 5% for all analyses. Twenty-five patients were re-evaluated 3 to 7 years after STN-DBS surgery, with a mean five-year postoperative follow-up. Clinical characteristics were age 64(5) y, 8/17 F/M, PD duration 16(5) y, distance from STN-DBS intervention 5(1) y, median (IQR) UPDRS-III 12(12), WHS 5(1), FAC 5(2). Most patients were able to perform the test in all conditions. Both STN-DBS alone and the combination of STN-DBS and medications led to an improvement of clinical motor scores and most iTUG parameters (p<0.001). In particular: 1) the elevation/sitting gestures and the turn phases differently improved in the different conditions; 2) on average, the effect of the DUAL TASK condition led to indices similar to those in the off-off condition 3) data from the DUAL TASK condition suggest the existence of two subgroups of patients, whose performance is either affected or not affected by the cognitive task ( Fig. 1 ). The protocol resulted feasible. Our results indicate that both STN-DBS and levodopa can improve walking ability even in the long-term after surgery. Results during DUAL TASK suggest the use of attentional strategies in the rehabilitation of selected patients, as indicated in the EU physiotherapy guidelines for PD [2]. A rehabilitative intervention should be strongly recommended in those patients whose performance in DUAL TASK becomes so impaired as in the STIM-OFF/MED-OFF, as measured by the iTUG. In conclusion, the iTUG test could be used in PD patients with STN-DBS to support the selection of tailored rehabilitative interventions and to identify patients whose performance is highly affected during cognitive tasks.