Objective: To determine the minimal clinically relevant change (MCRC) of the FOG score.

Background: Despite recent advances in the field of FOG research, the assessment of this elusive gait phenomenon in the clinical setting is a challenge. We developed an evaluation instrument that was suggested for further use by the MDS committee (1,2). Main critique points were the lack of responsiveness data, and scarce information concerning its validity. Here, we present data on the MCRC and correlations to free-living observations.

Methods: FOG scores were evaluated before and 30 minutes after taking a regular levodopa dose. Between the FOG assessments the patient took a 20 minutes hospital walk simulating a free living situation. The tour and the scoring tasks were recorded on video and rated offline using ANVIL 6 (Augsburg, Germany)(3). Both patient and expert rater assessed the change in FOG on a 7-step Likert-typed scale [-3;+3]. The MCRC was calculated using the ROC approach with the expert’s or the patient’s evaluation as event value (rating of >0). Total duration (s) of FOG episodes and Festination episodes during free living were cumulated to the Time Spent Frozen (TSF). Total duration (s) of walking episodes, excluding Festination and climbing stairs were cumulated to the Time Spent Walking (TSW). The FOG Ratio was calculated as TSF divided by TSW.

Results: 40 patients (29 male/11female) were recruited, 36 completed both FOG-Score ratings, 28 completed all tasks. Mean HY stage (OFF) was 3. Patients scored an average of 11 points on the FOG-Score. Mean Change in FOG-Score was 4.5. The MCRC was calculated as a change of 2 points for both the rater’s and the patient’s evaluation. Mean Time spent walking during free living was 795 s, mean TSF was 147 s. The FOG ratio and the mean FOG score were moderately correlated with a Rho of 0.72 (p<0.0001).

Conclusions: This is the first report of the MCRC of the FOG score, a clinical evaluation instrument for FOG. The MCRC of 2 demonstrates that the FOG-score is able to detect subtle changes that were considered relevant by the bystanding expert as well as the patient. The ample correlation between FOG score and free-living experience support the validity of the FOG score. This data support the further use of the FOG score in clinical research.

References: 1. K. Ziegler, F. Schroeteler, A.O. Ceballos-Baumann, U.M. Fietzek, A New Rating Instrument to Assess Festination and Freezing Gait in Parkinsonian Patients. 2010, Mov Disord, 25(8) pp1012-8. 2. B. Bloem, J. Marinus, Q. Almeida et al. Measurement Instruments to Assess Posture, Gait, and Balance in Parkinson’s Disease: Critique and Recommendations. 2016, Mov Disord, 31(9) pp1342–55. 3. M. Kipp. Anvil – A Generic Annotation Tool for Multimodal Dialogue. 2001. Proc of the 7th Eur Conf on Speech Comm and Technol (Eurospeech), pp. 1367-1370.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/the-fog-score-detects-relevant-changes-of-gait-freezing-for-patients-and-experts/