There is little agreement on which outcome measures to use to express the efficacy of treatments for cervical dystonia. We analyzed change scores on various scales of 64 new patients with cervical dystonia before and after repeated injections with botulinum toxin.
Method: The association between change in impairment (Tsui), and change in pain (TWSTRS-Pain) and functional health (TWSTRS-D, MOS-20) was expressed in percentages of variance explained. Effect sizes of the outcome measures from patients who continued botulinum treatment and dropouts were compared. Performance of outcome measures to distinguish patients who continued treatment and dropouts was analyzed with ROC curves and areas under the curve (AUC).
Results: Impairments explained < or =7% of the score variance in functional health. There were no differences between the effect sizes of impairment and pain of patients who continued treatment and dropouts (p > 0.60). This suggests a poor reflection of the treatment efficacy by these outcome measures. Conversely, there were significant differences between the effect sizes of the functional status scales of the patients who continued treatment and the dropouts (p < or = 0.01). ROC curve analysis showed that the disability, handicap, and global disease burden scale accurately distinguished between the two groups (AUCs > 0.80). Impairments showed no discriminative accuracy (AUC = 0.46).
Conclusion: Neurologic impairments have a small impact on the functional health of cervical dystonia patients. Disability, handicap, and a global measure of disease burden were the most suitable outcome parameters to express the clinical efficacy of botulinum therapy.