Utilizing Kinematic Analysis of Postural Instability as an Objective Measure to Aid in the Diagnosis of Normal Pressure Hydrocephalus

Thursday, September 21, 2023

3:40 PM – 3:50 PM CT

Location: Los Angeles - Miami - Scottsdale, 5th Floor

Member Speaker(s)

JH

Jacob T. Hanson, BA

Medical Student
Rocky Vista University College of Osteopathic Medicine
Rocky Vista University College of Osteopathic Medicine

Disclosure(s): No financial relationships to disclose

Slides

Disclosure(s):

Jacob T. Hanson, BA: No financial relationships to disclose

Learning Objectives:

Upon completion, participant will be able to identify the significance of clinical research with movement disorder patients.
Upon completion, participant will be able to define quantitative kinematics and apply it to movement disorder research.
Upon completion, participant will be able to describe the differences in postural instability among Parkinson's disease and normal pressure hydrocephalus patients at baseline kinematic testing.

Introduction/Purpose: Patients with normal pressure hydrocephalus (NPH), often characterized as a type of parkinsonism, are underdiagnosed and undertreated, and typically present with a classical triad of gait, cognitive, and urinary symptoms, making differentiating between NPH and Parkinson’s disease (PD) difficult at baseline evaluation. Postural instability (PI), or the inability to maintain an upright posture given a perturbation or change in environment, is a clinical feature present in both PD and NPH and can significantly decrease quality of life and increase mortality within these patient groups. Traditionally, gait and PI are measured with ordinal rating scales, such as the Unified Parkinson’s disease rating scale pull test (UPDRSPT) and Mini- Balance Evaluation Systems Test (Mini-BEST). However, these evaluations produce highly variable and subjective results depending on the provider, making it difficult to ascertain surgical candidacy and the potential benefit of surgical intervention for these patients. Alternatively, our previous work has identified a quantitative kinematic system of evaluation as both efficient and more objective in measuring gait and postural instability. With this method, patients are equipped with inertial measurement units (IMUs) and are examined with purposely varied pull intensities (i.e., a spectrum from very easy pulls to very hard pulls). This kinematic approach to evaluating PI theoretically reduces inter-provider variability by quantifying the inherent variability in the exam maneuver and provides more objective insight into a patient’s disease process. We sought to investigate the use of kinematic assessment of PI using IMUs and the UPDRSPT scale as a mechanism of differentiation between the two disease processes at baseline evaluation.

Methods or Case Description: 20 patients with NPH, 55 patients with PD, and 56 age-matched, healthy controls underwent quantitative pull test examinations while wearing IMUs at baseline. Center of mass and foot position data were used to compare velocity and acceleration profiles, pull test step length, and reaction times between groups and as a function of UPDRSPT score. NPH patients participated in 20 baseline sessions with a mean of 15.1 pull test trials per session, for a total of 306 trials across patients. PD patients participated in 55 baseline sessions with a mean of 13.47 pull test trials per session, for a total of 740 trials across patients. The healthy age-matched control participants participated in 56 evaluation sessions with a mean of 14.79 pull test trials per session, for a total of 827 trials across subjects.

Outcomes: Overall, the reactive postural response of NPH patients was characterized by slower reaction times and smaller steps compared to both PD patients and healthy controls. However, when patients were grouped by UPDRSPT scores, no reliable objective difference between patient groups was detected in terms of mean reaction time or step length. At their initial evaluation, very few NPH patients demonstrate “normal” or “mild” PI as they appear to be older upon presentation compared to PD patients. As a result, kinematic assessment utilizing IMUs may not be helpful for differentiating between NPH and PD as a function of UPDRSPT score, but rather as a more fine-tuned method to define disease progression.

Conclusion: To our knowledge, there are no previous studies that examine differences in postural instability with quantitative kinematic assessment as an objective tool to distinguish between patients with NPH and PD. Using quantitative kinematic analysis, significant decreases exist in overall VCOM, scaled reaction time, and scaled step length for NPH patients as opposed to their PD counterparts. This is mainly due to the severity of presentation as NPH patients as a group were more likely to present with worse balance. When we examined these differences grouped by the current gold standard evaluation for postural instability, namely the UPDRSPT score, there were no reliable objective difference between NPH and PD patients. This may actually be an advantage for future studies aimed at examining the underlying mechanisms of postural instability since NPH patients improve with treatment whereas PD patients do not. Given the insights into the initial presentation, management and monitoring treatment response of postural instability in movement disorder patients, we would advocate for further incorporating objective kinematic data collection into their clinical visits.