Resting state Functional Connectivity differences in Pediatric Patients with Tourette syndrome and Obsessive-compulsive disorder

Objective: To assess functional connectivity (FC) abnormalities contributing to the pathophysiology of Tourette syndrome (TS) and obsessive-compulsive disorder (OCD) in pediatric patients. Background: TS is a neurodevelopmental disorder that is frequently associated with psychiatric comorbidities, including OCD. Several clinical features seem to distinguish the “pure” form of OCD from the “tic-related” one. Although FC has been investigated in both disorders separately, no study has compared functional abnormalities in pediatric patients with either TS or OCD. Method: 30 TS, 10 OCD, and 11 Healthy controls (HC), aged 8-14 years, underwent 3T resting-state fMRI. Yale Global Tic Severity Scale (YTGSS) and Children Yale-Brown Obsessive-Compulsive Scale (CYBOCS) assessed tic severity and OCD symptoms, respectively. fMRI data were processed by using FSL. After image pre-processing, independent component analysis decomposed the data into 30 spatial components. Seven networks of interest were selected, i.e. Basal Ganglia (BG), Cerebellum (CB), Frontoparietal (FP), Default- Mode (DMN), Orbitofrontal (OBF), Salience (SN), Sensorimotor Network (SMN), to investigate betweengroup differences in FC and clinical correlations (p<0.05, FDR corrected). Customized children T1 template was used for analysis. Results: Patients with TS showed higher FC in the BG, CB, DMN, and SMN and lower FC in FP and SN than HS. Patients with OCD showed higher FC in the CB, FPN, SN, SMN than HS and higher FC in CB and FP than TS subjects. Differences between OCD and TS persisted even when splitting the TS group into pure-TS (scoring 0 in CYBOCS, n=16) and TS plus OCD (scoring more than 0 in CYBOCS, n=14). In TS patients, YTGSS scores positively correlated with FC in BG and SMN and negatively with CB and FP. In OCD patients, CYBOCS scores positively correlated with FC in FP and SMN, and negatively with CB. Conclusion: Our results con rm the role of sensorimotor networks in TS pathophysiology and their relationship with tic severity. An increased FC in CB and FP networks characterizes OCD and distinguishes it from TS; this finding persisted also when comparing OCD withTS plus OCD patients, suggesting different neural underpinnings in these two disorders.