Fig. 2.

Evaluation of treatment efficacy in TS in light of natural waxing and waning. At date 1 a therapeutic intervention could be followed by tic reduction despite of its potential to increase tics or without an effect on tics. This has to be ascribed not to causal mechanisms of the intervention but to the natural waxing and waning of the tics. Correspondingly, a therapeutic intervention at date 2 could be followed by an increase of TS symptomatology despite its potential to reduce tics. The therapeutic intervention might attenuate the natural waxing of the tics. Conclusion: Meaningful appraisal of treatment efficacy in TS can only be given in most cases after longer time