Foot Function Index: a promising questionnaire for patients with Charcot-Marie-Tooth disease type 1A

Abstract Objective To evaluate in a preliminary methodological study, the Foot Function Index (FFI), a 3-subscale (pain, disability and activity restriction) foot disability assessment questionnaire, in patients with Charcot-Marie-Tooth disease type 1A (CMT1A). Design Monocentric exploratory cross-sectional study with 2 identical evaluations by the same Physical Medicine and Rehabilitation physician at 14-day intervals (test–retest) according to international guidelines for validating health-related patient-reported outcomes (COSMIN criteria). Setting Physical Medicine and Rehabilitation and Neurology departments in a French academic hospital. Participants Twenty-six patients with CMT1A confirmed by molecular biology. Intervention The FFI and a health-related quality of life questionnaire (Medical Outcomes Study Short Form 36 [SF-36] with mental and physical composite scores) combined with quantitative walk analysis by GAITRite® and evaluation of isokinetic quadriceps and hamstrings peak torque by CybexHumanNorm®. Main Outcome Measures FFI score and its dimensions. Results Acceptability was satisfactory, with less than 5% missing data and good distribution of results. Internal consistency was very satisfactory, with Cronbach alpha 0.95. Reproducibility was very satisfactory, with Lin concordance coefficient 0.82. External consistency was satisfactory, with expected correlation coefficients: the FFI was significantly correlated with the SF-36 physical composite score and gait parameters (cadence) (r=-0.58 and r=-0.52, p Conlusion This study confirms the very good metrological properties of the FFI in patients with CMT1A. The FFI could be a promising questionnaire to assess foot-related disability in a neurologic disease. Complementary studies are still needed to confirm these promising preliminary results.