Quantitative evaluation of the effects of subthalamic stimulation on gait in Parkinson's disease patients using principal component analysis

A M S Muniz, H Liu, K E Lyons, R Pahwa, W Liu, J Nadal
International Journal of Neuroscience 2010, 120 (9): 609-16

BACKGROUND: Principal component analysis (PCA) was applied to the ground reaction force (GRF) for evaluating the deep brain stimulation of the subthalamic nucleus (DBS-STN) effects in Parkinson's disease (PD) subjects with and without medication.

METHODS: Ten subjects who underwent DBS-STN were evaluated under the following four conditions: without treatment (mof-sof), with stimulation (mof-son), with medication (mon-sof), and with both treatments (mon-son). A control group of 30 subjects was also evaluated. PCA was applied separately on each GRF component. Broken stick criterion selected eight principal components (PC) from vertical GRF and one from each horizontal GRF. A standard distance was calculated using these 10 PCs and the gait speed to measure how far the PD group's gait was from the normal pattern.

RESULTS: The standard distance allowed classifying normal and PD subjects in the mof-sof condition with 100% accuracy, sensitivity, and specificity. The same distance was calculated for mon-sof, mof-son, and mon-son conditions. The smallest mean standard distance was found in the mon-son condition, which was significantly different from mof-sof (Friedman test with Dunn post-hoc, p < .05).

CONCLUSION: PCA allowed the quantitative evaluation of treatment effects, indicating that DBS-STN improves the GRF pattern in PD subjects, primarily in the medication on state.

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