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Development and Validation of the Orthostatic Tremor Severity and Disability Scale (OT-10)
Aristide Merola1, Diego R Torres-Russotto2, Glenn T Stebbins3
1Department of Neurology, The Ohio State University Wexner Medical Center, Columbus, Ohio, USA.
Background:
Limited tools are available for the assessment of orthostatic tremor severity and disability.
Objectives:
To develop and validate a self-administered orthostatic tremor scale.
Methods:
After expert consensus and literature review generating a list of 42 items, the scale was developed and modified for validation after a patient focus group, multiple rounds of Delphi panels, and cognitive interviews. Clinimetric evaluations included assessing content validity, internal consistency, measurement error and reliability, construct validity, and concurrent validity anchored on the examiner's Clinical Global Impression score.
Results:
Eleven items ranked on a Likert scale from 0 (no disability/severity) to 5 (maximal disability/severity) were evaluated in 54 orthostatic tremor patients (16 men and 38 women; mean age: 69.17 ± 9.64 years; disease duration: 13.83 ± 11.24 years) to probe severity and disability over the preceding 1-week period. The 11-item scale showed good internal consistency (Cronbach's alpha = 0.863) and acceptable (>0.40) item-to-total correlation. However, one item was removed at the final Delphi panel because of significant floor effect, poor item-to-total correlation, and poor factor-loading, leaving the scale with 10 items (10-item Orthostatic Tremor Severity and Disability Scale). Test-retest reliability at 2 weeks was excellent (two-way random intraclass correlation coefficient > 0.90), and the individual item test-retest reliability showed good agreement, with a threshold weighted kappa >0.60 for all items. Exploratory factor analyses revealed a parsimonious two-factor construct accounting for 57.7% of the scale's variance. The 10-item Orthostatic Tremor Severity and Disability Scale scores correlated with the CGI.
Conclusions:
The self-administered 10-item Orthostatic Tremor Severity and Disability Scale scale is valid and reliable for capturing orthostatic tremor-related severity and disability. © 2020 International Parkinson and Movement Disorder Society.
