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Developing Outcome Measures for Assessing Freezing of Gait: A Multi-Center Study

Study Rationale: Standardized and accurate assessment of freezing of gait (FOG), a debilitating symptom of Parkinson’s disease (PD), is needed to develop and rigorously test novel therapies. However, measurement of FOG severity is challenged by imprecise definitions and the absence of well-validated clinical outcome measures. The urgency of this problem prompted an International Consortium of FOG (IC-FOG) that included 50 experts to achieve consensus for a new definition of FOG and to develop a Clinician-Reported Outcome (ClinRO), a Patient Reported Outcome (PRO), and a standardized approach for using wearable sensors for “smart-scoring” of the ClinRO. The goals of this multi-center study are to validate the new ClinRO for FOG and to further develop a new PRO to enable meaningful advances in treatment strategies for people living with FOG.

Hypothesis: Our new ClinRO and PRO for FOG, based on new, precise definitions of FOG, will be valid and reliable methods for assessing the severity of FOG in people with PD, addressing many of the gaps in current options and meeting the needs for both clinical trials and clinical practice.

Study Design: 105 participants with PD who experience FOG will complete a 6-minute assessment of FOG (e.g., walking, turning, dual-tasking and negotiating a doorway) in their Off-medication state and then repeat this in their On-medication state across 7 international sites. This will be carried out twice, on separate days, to evaluate the test’s reliability and validity. Participants will wear inertial sensors and a video recording will capture the FOG episodes that were provoked during the assessment. FOG severity will be scored in real-time by trained raters, and video recordings will be annotated by experts to determine the agreement between gold standard measures based on the video annotations and the real-time ClinRO score. Detailed interviews will be used to evaluate and further refine the PRO and a plan for seeking regulatory approval will be generated.

Impact on Diagnosis/Treatment of Parkinson’s disease: The project will lead to a standard, validated toolkit and training materials that can enable clinicians, researchers, and industry stakeholders to reliably evaluate FOG severity. The anticipated new, valid and reliable clinician-reported outcome measure of FOG and developments in the PRO are essential for evaluating the efficacy of new treatments for FOG.

Next Steps for Development: The next steps will include further evaluation of different aspects of validity (e.g., predictive abilities, response to interventions like DBS), developing training materials, translation and validation of the material to other languages, developing a technology-based solution for automated, smart-scoring of the ClinRO and of FOG severity during daily life, and work toward regulatory approval.


  • Jeffrey M. Hausdorff, PhD

    Tel Aviv Israel

  • Jorik Nonnekes, MD, PhD

    Nijmegen Netherlands

  • Kaylena Ehgoetz Martens, PhD

    Waterloo ON Canada

  • J. Lucas McKay PhD, MSCR

    Atlanta, GA United States

  • Jamie L. Adams, MD

    Rochester, NY United States

  • Martina Mancini, PhD

    Portland, OR United States

  • Moran Gilat, PhD

    Leuven Belgium

  • Simon John Geoffrey Lewis, MBBCh BSc MRCP FRACP MD

    Sydney NSW Australia

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