In this presentation Prof Simon Lewis explains why freezing of gait (FOG) is such a significant and challenging symptom in Parkinson’s disease, and why an updated definition matters for both clinical care and research. It is well known that FOG can appear in different situations such as when medication wears off, during turning (including tight turns like in bathrooms), when dual-tasking (walking while thinking or talking), and when approaching narrow spaces such as doorways. These episodes are dangerous because people may continue to push forward despite their feet “sticking”, increasing the risk of falls. Around 80% of patients will develop FOG over the course of their condition and it is a major driver of reduced quality of life. While physiotherapy, medication adjustment, deep brain stimulation, other stimulation methods, and neuropsychiatric approaches (including addressing anxiety) can help, no current treatment is reliably effective for everyone. This makes high-quality research and clinical trials essential. Professor Simon Lewis outlines how the international field has worked collaboratively to standardise our understanding of FOG. In 2026, an International Consortium for FOG (IC-FOG) released an updated clinical definition of FOG and a complementary technical definition to support the precise video-based measurement of FOG, enabling millisecond-level timing and consistent scoring. The IC-FOG is also developing certification for raters, clinician-rated outcome measures using standardised tasks, and patient-reported outcomes to ensure assessments reflect what patients experience and what regulators require for future treatment approvals.
