An Observational Longitudinal Study on Seasonal Variations in Tourette Syndrome: Evidence for a Role of Ambient Temperature in Tic Exacerbation

Tourette syndrome (TS) is a high-incidence neurobehavioral disorder that generally begins in childhood. Several factors play a role in its etiology, including genetic influence and auto-immune activation by streptococcal infections. In general, symptoms subside after the end of adolescence, but, in a significant number of patients, they remain in adulthood. In this study, we evaluated temporal variations in the two core clinical features of TS including tics and obsessive–compulsive disorder (OCD) symptoms. An observational longitudinal study lasting 15 months (2017–2019) was conducted on a cohort of 24 people recruited in Milan (Italy) who were diagnosed with a subtype of TS known as obsessive–compulsive tic disorder. Inclusion criteria included a global score of the Yale global tic severity scale (Y-GTSS) > 50, a Yale–Brown obsessive–compulsive scale (Y-BOCS) global score > 15, and TS onset at least one year prior. Y-GTSS and Y-BOCS data were acquired at six time points, together with local environmental data. Tics, but not OCD symptoms, were found to be more severe in spring and summer compared with winter and autumn (p < 0.001). Changes in tics displayed an appreciable oscillation pattern in the same subject and also a clear synchrony among different subjects, indicating an external orchestrating factor. Ambient temperature showed a significant correlation with Y-GTSS measurements (p < 0.001). We argue that the increase in tics observed during hot seasons can be related to increasing ambient temperature. We believe that our results can shed light on the seasonal dynamics of TS symptomatology and provide clues for preventing their worsening over the year.