Objective: Stability evaluation is of much value for staging the disease according to the Hoehn and Yahr (HY) scale. We propose to correlate a dynamic postural stability evaluation with pull test item of UPDRS evaluation in order to evidence the limitations of a subjective scale to rate stability and disease progression.

Background: Postural instability is a characteristic of PD as the disease progresses and is associated with an increased risk of falls. UPDRS is used to assess the severity of the disease and is related with the HY stages of the disease according to the presence of symptoms in one or both sides or alteration in posture, stability or gait. A critic point for stability evaluation is the pull test, it depends largely in the examiners technique for the pull test (PT) and expertise for interpretation. The PT assesses the response of a standing patient to a forceful and rapid pull backward but it has been shown to fail to predict future falls in PD. Falls are intimate associated with the limit of stability (LOS) area, that is reduced in PD compared to healthy people, its evaluation does not include external perturbations, so it can reflect a more ecologic and real situation in daily life.

Methods: 30 PD patients (24 male; age 63±9 and 6 female; age 65,5±12) , HY stage I to III (“ON”UPDRS III 16±7) were evaluated same day for UPDRS part III and LOS test consisting on standing on the platform and leaning in eight directions to make a cursor displayed on the system’s screen hit a target. Higher scores indicate better performance. 24 age and sex matched healthy controls LOS evaluation was used to define the normal distribution of scores. (≥ 41.75) equivalent to 0, lower scores were divided in 4 quartile and asigned values from 1 to 4 correlative to UPDRS PT item. UPDRS part III was recalculated using these values and HY severity was reassessed.

Results: Kappa index between Pull test and LOS was 0,175(-0,090,0,440). With scores derived from LOS evaluation, 56,67% of PD subjects increased their total UPDRS III (range 1 to 3 pt) and just one case decreased 1 point. When severity was reassessed 53% increased their HY scale. 15 out of 30 patients passed to stage 3 because of evidence of postural instability.

Conclusions: Pull test underestimates postural instability in PD patients thus is also underscoring HY disease progression. This can lead to a lower awareness of the risk of falls in PD patients.

References: Kim, Samuel D., Natalie E. Allen, Colleen G. Canning, and Victor S. C. Fung 2013 Postural Instability in Patients with Parkinson’s Disease. Epidemiology, Pathophysiology and Management. CNS Drugs 27(2): 97-112. Nonnekes, Jorik, Rianne Goselink, Vivian Weerdesteyn, and Bastiaan R. Bloem 2015 The Retropulsion Test: A Good Evaluation of Postural Instability in Parkinson’s Disease? Journal of Parkinson’s Disease 5(1): 43-47.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/impact-of-postural-stability-estimation-in-hy-scale-pull-test-vs-limits-of-stability-assessment/