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Research paper
Defining disability: development and validation of a mobility-Disability Severity Index (mDSI) in Charcot-Marie-tooth disease
  1. Sindhu Ramchandren1,
  2. Michael Shy2,
  3. Eva Feldman1,
  4. Ruth Carlos3,
  5. Carly Siskind4
  1. 1Department of Neurology, University of Michigan, Ann Arbor, Michigan, USA
  2. 2Department of Neurology, University of Iowa, Iowa City, Iowa, USA
  3. 3Department of Radiology, University of Michigan, Ann Arbor, Michigan, USA
  4. 4Department of Neurology, Stanford Hospital and Clinics, Stanford, California, USA
  1. Corrrespondence to Dr Sindhu Ramchandren, Department of Neurology, University of Michigan, 2301 Commonwealth Blvd #1023, Ann Arbor, MI 48105, USA; sindhur{at}med.umich.edu

Abstract

Objective To develop and validate a reliable patient-reported scale that grades the severity of disability in Charcot-Marie-tooth disease (CMT), from an in-depth analysis of patient and healthcare provider perspectives on what mobility changes constitutes mild, moderate and severe disability.

Design In this prospective, cross-sectional study, a 19-item Disability Questionnaire was developed following literature and expert review. Between 2011 and 2012, the Disability Questionnaire was provided to healthcare providers experienced in CMT attending national scientific meetings, and to patients self-registered with the Inherited Neuropathy Consortium—Rare Diseases Clinical Research Consortium on-line contact registry. Provider and patient responses were compared utilising a two-sided unpaired t test with Bonferroni correction. The questionnaire was then assessed for validity, reliability and unidimensionality.

Results We analysed 259 Disability Questionnaires (167 patients, 92 providers); these showed perfect agreement between patient and provider responses on qualitative descriptions of disability, but significant differences in quantitative responses on items corresponding to minimal or severe disability (p<0.001). Validity and test–retest reliability of the questionnaire was excellent (Cronbach's α=0.96; intraclass correlation coefficients (ICC)=0.977 (0.951 to 0.993). Exploratory factor analysis and the Mokken Scaling Procedure supported the unidimensionality of the mobility-Disability Severity Index.

Conclusions The mobility-Disability Severity Index is a unique instrument, categorising disability from the patient's perspective, and will undergo further cross-validation studies in CMT.

  • Hmsn (Charcot-Marie-Tooth)
  • Neuromuscular
  • Neuropathy

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