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

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).

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.

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

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

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.

FFI score and its dimensions.

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.

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.