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International Parkinson and Movement Disorder Society

        VOLUME 30, ISSUE 2 • June 2026.  Full issue »

The next step in evaluating freezing of gait: New consensus definitions

Freezing of gait (FOG) impacts many people living with Parkinson’s disease (PD), with many losing their independence due to FOG as the disease progresses1. Current therapies for FOG are often ineffective, and progress in developing new treatments has been limited by a lack of standardization across definition and measurement1. Existing patient-reported outcomes are limited by high test-retest variability2, while wearable sensor-based objective outcomes are still pending further validation prior to real-world implementation3. Video annotation of FOG events during a variety of gait tasks has served as our gold standard for evaluating the severity of FOG4,5, however, such expert-based scores have lacked a precise definition to determine the start and end of each episode, leading to unwanted variability across studies6. To address these limitations, the International Consortium for Freezing of Gait (ICFOG) convened a working group to establish an updated consensus-based definition of FOG to unify the methodology on how to obtain the ground-truth measure of its severity.

Following extensive and spirited discussions, the ICFOG working group recently published both an updated clinical definition (for academic communication and use ‘at the bedside’) and a new technical definition that aimed to unify the scoring of FOG episodes and their various phenotypes from video recordings7. The 2026 clinical definition of FOG now reads: “Paroxysmal episodes wherein there is an inability to step effectively, despite attempting to do so”7. This definition extends an earlier definition by resolving its ambiguities8 and emphasizes that FOG events occur suddenly and unexpectedly and last for a particular duration. Whether the observed attempt to step is effective or not should be judged relative to the typical stepping performance observed in the same patient performing a similar task under similar conditions7.

The technical definition further explains how to determine the precise onset and termination of FOG episodes from video recordings in different scenarios. It also provides clear instructions on how to score and label the various leg movements that can be observed during FOG, when it is clinically or scientifically relevant to do so. Periods of complete cessation in foot progression are annotated separately as ‘core’ periods of the freeze events, independent of the leg movements observed. In addition, three main manifestations of leg movements can be differentiated, namely “Kinetic-trembling,” visible as fast oscillatory movements in the lower limbs; “Kinetic-no-trembling,” visible as any other ineffective movement in the lower limbs; and “Akinetic,” visible as an absence of observable movement in the lower limbs7. The akinetic manifestation thereby corresponds to core periods, but not vice versa, as core periods can also crop up during the other manifestations of FOG.

Ongoing work is now validating these definitions and evaluating whether a training program for raters can further improve consistency (NCT06519279). Unifying the definition of FOG and its phenotypes will allow for the evaluation of future objective clinical and patient-reported measures. The ICFOG believes that detailing the definition of FOG will help to advance research in the field and facilitate the development and evaluation of future interventions for FOG that will, hopefully, translate into better therapies for our patients.

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References:

  1. Lewis, S. et al. Stepping up to meet the challenge of freezing of gait in Parkinson’s disease. Translational Neurodegeneration 11, doi:10.1186/s40035-022-00298-x (2022).
  2. Hulzinga, F. et al. The New Freezing of Gait Questionnaire: Unsuitable as an Outcome in Clinical Trials? Mov Disord Clin Pract 7, 199–205, doi:10.1002/mdc3.12893 (2020).
  3. Mancini, M. et al. Technology for measuring freezing of gait: Current state of the art and recommendations. J Parkinsons Dis, 1877718X241301065, doi:10.1177/1877718X241301065 (2025).
  4. Gilat, M. How to Annotate Freezing of Gait from Video: A Standardized Method Using Open-Source Software. Journal of Parkinson's Disease 9, 821–824, doi:10.3233/jpd-191700 (2019).
  5. Zoetewei, D. et al. Which Gait Tasks Produce Reliable Outcome Measures of Freezing of Gait in Parkinson's Disease? J Parkinsons Dis 14, 1163–1174, doi:10.3233/JPD-240134 (2024).
  6. Cockx, H., Klaver, E., Tjepkema‐Cloostermans, M., Van Wezel, R. & Nonnekes, J. The Gray Area of Freezing of Gait Annotation: A Guideline and Open‐Source Practical Tool. Movement Disorders Clinical Practice 9, 1099–1104, doi:10.1002/mdc3.13556 (2022).
  7. Gilat, M. et al. An updated definition of freezing of gait. Nat Rev Neurol 22, 172–181, doi:10.1038/s41582-025-01179-3 (2026).
  8. Nutt, J. G. et al. Freezing of gait: moving forward on a mysterious clinical phenomenon. The Lancet Neurology 10, 734–744, doi:10.1016/s1474-4422(11)70143-0 (2011).

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