Foot Function Index: A Promising Questionnaire for Individuals With Charcot-Marie-Tooth Disease Type 1A

Abstract

Objective: To evaluate in a preliminary methodologic 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, the Consensus-based Standards for the Selection of Health Measurement Instruments Criteria.

Setting: Physical medicine and rehabilitation and neurology departments in a French academic hospital.

Participants: Patients with CMT1A confirmed by molecular biology (N=26).

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 instrumental gait analysis and evaluation of isokinetic quadriceps and hamstrings peak torque by isokinetic dynamometer.

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 α of 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<.005) but not with peak torque or SF-36 mental composite score.

Conclusions: This study confirms the very good metrologic 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.

Trial registration: ClinicalTrials.gov NCT01750710.

Keywords: Charcot-Marie-Tooth disease; Rehabilitation.