An updated definition of freezing of gait
Commentary by Dr. Nicholas D’Cruz
The recently published updated definition of freezing of gait (FOG) represents a much‑needed step toward standardizing both the terminology and the conceptual scope of this complex phenomenon. It is the culmination of nearly three years of discussions, iterative revisions, and “intensive debates.”
The well-known heterogeneity of FOG presentations makes the task of creating a one-line all-encompassing definition no easy feat. Yet, the new clinical definition manages to accomplish this by clarifying aspects of the original Nutt et al. definition while retaining the need for clinicians to apply their expert judgment. For research purposes, the technical definition also simplifies the spectrum of FOG into just three manifestations—kinetic trembling, kinetic non‑trembling (including episodic shuffling and freezing‑festination), and akinetic FOG. Although it is yet unclear whether these manifestations have distinct pathophysiology, this structure will likely enhance consistency in clinical trial outcomes and algorithm development.
Equally useful is the proposed FOG classification system distinguishing possible, probable, and definite freezers and non‑freezers. This approach acknowledges clinical uncertainty and reduces ambiguity in cohort selection, thereby strengthening investigations into the mechanisms and modifiers of FOG.
Although the working group comprised both clinical experts and experienced FOG raters, a possible limitation is the absence of the perspective of people living with FOG. The ongoing efforts to develop a patient-reported outcome of FOG, validated against the gold-standard video ratings will be an important step towards bridging the gap between phenomenology and lived experience. Moreover, as algorithms learn from standardized FOG annotations, we can expect sensor-based methods to replace the need for time-consuming video ratings. Ultimately, this consensus statement sets the stage for more impactful work to alleviate the burden of people living with FOG.
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