Reliability and validity of the CMT neuropathy score as a measure of disability

Objective: To determine the validity and reliability of the Charcot-Marie-Tooth disease (CMT) neuropathy score (CMTNS) in patients with inherited neuropathy. Background: Natural history studies and potential treatment trials for patients with various forms of CMT are limited by the lack of quantitative methodologies to monitor disease progression. Most cases of CMT can be considered length-dependent axonal neuropathies because disability for even the demyelinating forms correlates with length-dependent axonal degeneration. The total neuropathy score (TNS) is a validated composite measure of disability in length-dependent axonal neuropathies but is weighted toward predominantly sensory neuropathies. Thus, the authors have devised a CMTNS, modified from the TNS, to provide a single measure to quantify CMT disability. Methods: The authors measured inter- and intrainvestigator reliability of the CMTNS and performed a validation of the score with the Neuropathy Impairment Score (NIS), patient self-assessment scores, an ambulation index, and other measures of disability. Results: Inter- and intrainvestigator reliability was more than 95% in the 60 patients evaluated. Patients could be divided into mild (CMTNS, <= 10), moderate (CMTNS, 11 to 20), and severe (CMTNS, >= 21) categories and demonstrated excellent correlations among all measures of disability. Conclusion: The Charcot-Marie-Tooth disease (CMT) neuropathy score is a validated measure of length-dependent axonal and demyelinating CMT disability and can be investigated as an end point for longitudinal studies and clinical trials of CMT.