Predisposing factors to pattern change in cervical dystonia.

Background: Cervical dystonia (CD) patterns may change with Botulinum toxin (BoNT) treatment.

Objective: To evaluate the time within those changes usually occur, the most predisposed phenotypes and predisposing factors.

Methods: We divided idiopathic CD patients into two groups- change YES and NO, collecting general clinical and demographic variables. We also evaluated duration of BoNT treatment, Tsui total scores and subscores - assessed at T0 - before BoNT start - and at T1- time to chenge in the YES group or last visit in the NO group. The risk of pattern change was assessed by Kaplan Meyer curves and Cox regression analysis. Finally, Multivariate linear regressions were employed to assess if Tsui severity correlated with the change.

Results: Among 100 patients (60 women), 37 experienced a phenotype switch, mostly in the first five years of BoNT treatment, YES and NO groups were comparable. Multivariate Cox Regression revealed the presence of laterocollis or rotatocollis at T0 as predictors of switch (respectively P = 0.01, HR = 3.5; P = 0.03, HR = 1.5). Multivariate linear regressions revealed that high Tsui subscores for the tilt and low Tsui total scores were risk factors for the change of pattern (respectively P = 0.002, OR = 6; P = 0.03, OR = 0.8).

Conclusions: Latero and Rotatocollis are the CD phenotypes most predisposed to change. CD characterized by neck tilt are more likely to change phenotype following treatment. Dystonias with a low degree of severity are more predisposed to switch. Both, the different degree of muscle activation and BoNT mechanism of action, may impact on that phenomenon.