A 2-year longitudinal follow-up of quantitative assessment neck tics in Tourette’s syndrome

Background
Neck motor tics in Tourette’s syndrome can cause severe neck complications. Although addressed in a few longitudinal studies, the clinical course of Tourette’s syndrome has not been quantitatively assessed. We had previously developed a method for quantifying the angular movements of neck tics using a compact gyroscope. Here, we present a follow-up study aimed at elucidating the clinical course of neck tics at both the group and individual levels.

Methods
Eleven patients with Tourette’s syndrome from our previous study participated in the present study, and their neck tics were recorded during a 5-min observation period. The severity of neck symptoms was assessed using the Yale Global Tic Severity Scale. The peak angular velocities and accelerations, tic counts, and severity scores in our previous study (baseline) and the present study (2-year follow-up) were compared at the group and individual levels. The individual level consistency between baseline and follow-up were calculated using intra-class correlation coefficients (ICCs, one-way random, single measure).

Results
At the group level, no significant change was observed between baseline and follow-up. At the individual level, angular velocity (ICC 0.73) and YGTSS scores (ICC 0.75) had substantial consistency over the two time points, and angular acceleration (ICC 0.59) and tic counts (ICC 0.69) had moderate consistency.

Conclusions
The intensity and frequency of neck tics did not change over time. Therefore, quantification of angular neck motor tics will aid in identifying patients with neck tics at high risk for severe neck complications.