The Charcot-Marie-Tooth functional outcome measure (CMT-FOM)

Abstract

Objective The purpose of this study was to examine the feasibility, reliability, and convergent validity of the Charcot-Marie-Tooth Functional Outcome Measure (CMT-FOM), a new performance-based measure assessing functional ability in adults with CMT disease. Methods Adults with CMT type 1A (CMT1A) were recruited at the Universities of Rochester and Iowa. Participants were assessed using the CMT-FOM, CMT Exam Score (CMTES), and a symptom report. Test-retest reliability was examined using intraclass correlation coefficients, internal consistency using Cronbach α, and convergent and known-groups validity using Spearman rank analysis and the Mann-Whitney test. Results Forty-three individuals (70% women; mean age 41, SD 14.9 years) participated. The CMT-FOM (mean 25.3 ± 8.7, range 12–44/52) was moderately correlated with the CMTES (ρ = 0.62; p < 0.0001) and exhibited acceptable reliability (intraclass correlation coefficient = 0.92) and internal consistency (Cronbach α = 0.81). The CMT-FOM discriminated between participants with clinically mild vs moderate-severe CMT1A. Participants with the mildest CMT1A who demonstrated a floor effect on the CMTES showed functional limitations on the CMT-FOM. Conclusions The CMT-FOM is well tolerated and showed no floor/ceiling effects in an adult CMT1A cohort matching those likely to enter upcoming clinical trials. It appears to be reliable, and our data support convergent and known-groups validity in adults with CMT1A. Longitudinal studies further examining the psychometric properties of the CMT-FOM and its responsiveness to change before its application in therapeutic trials are necessary.