Measurement properties of the Boston Carpal Tunnel Questionnaire in subjects with neurophysiological confirmation of carpal tunnel syndrome: a Rasch analysis perspective.

Purpose: To perform a comprehensive psychometric analysis of the Boston Carpal Tunnel Syndrome Questionnaire (BCTQ) by means of factor and Rasch analyses in subjects with neurophysiologic confirmation of carpal tunnel syndrome (CTS). Relationship between clinical severity assessed with the log-linear version of the BCTQ and neurophysiologic severity assessed with nerve conduction studies was further examined.

Methods: Five hundred and twenty-eight individuals completed the questionnaire. Confirmatory and exploratory factor analyses were used to determine the latent structure of the BCTQ. Through Rasch methodology, a log-linear version was proposed given the latent structure of the questionnaire. Linear relationship between the proposed questionnaire and neurophysiologic findings was established.

Results: The BCTQ underlying structure comprises, at least, three factors that may be represented by Functionality, Paresthesia and Pain domains. Two log-linear subscales may be proposed: subscale 1 comprised of the Functionality factor and subscale 2 which incorporates the Paresthesia and Pain factors under a bifactor solution. Neurophysiologic and clinical severity classification system displays a very weak linear correlation.

Conclusion: A log-linear version of the BCTQ, useful as an outcome tool in clinical and trial settings, is proposed. Neurophysiological data lack the ability to resemble changes in clinical status of individuals with CTS.