BACKGROUND: Although an increasing number of trials are reported on the 
treatment of generalized or segmental isolated dystonia, the minimal clinically 
important difference thresholds for the most frequently reported outcome 
measures are still undetermined.
OBJECTIVES: To estimate the minimal clinically important difference for the 
Burke-Fahn-Marsden Dystonia Rating Scale and the 36-Item Short-Form Health 
Survey in generalized or segmental dystonia.
METHODS: A total of 898 paired examinations of 198 consecutive patients, aged 
>18 years, with idiopathic and inherited (torsin family 1 member A positive) 
segmental and generalized isolated dystonia were analyzed. To calculate the 
minimal clinically important difference thresholds, both anchor- and 
distribution-based methods were used simultaneously.
RESULTS: Any improvement >16.6% or worsening larger than 21.5% on the 
Burke-Fahn-Marsden Dystonia Rating Scale indicates a minimal, yet clinically 
relevant, change. Threshold values for the Burke-Fahn-Marsden Dystonia 
Disability Scale were 0.5 points for both decline and improvement. Cut-off 
scores for the Physical Component Summary, the Mental Component Summary, and the 
Global (Total or Overall) Score of the 36-Item Short-Form Health Survey were 5.5 
and 5.5, 6.5 and 7.5, and 7.5 and 8.5 points for clinically meaningful 
improvement and deterioration, respectively.
CONCLUSIONS: The minimal clinically important difference represents the smallest 
change in an outcome measure that is meaningful to patients. Our estimates for 
the Burke-Fahn-Marsden Dystonia Rating Scale and the 36-Item Short-Form Health 
Survey may allow more reliable judgment of the clinical relevance of different 
treatments for segmental and generalized isolated dystonia. © 2020 The Authors. 
Movement Disorders published by Wiley Periodicals, Inc. on behalf of 
International Parkinson and Movement Disorder Society.