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 ofTourette syndrome (TS) and obsessive-compulsive disorder (OCD) in pediatric patients.Background: TS is a neurodevelopmental disorder that is frequently associated with psychiatriccomorbidities, 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 comparedfunctional 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 imagepre-processing, independent component analysis decomposed the data into 30 spatial components. Sevennetworks 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 betweengroupdifferences in FC and clinical correlations (p<0.05, FDR corrected). Customized children T1 templatewas used for analysis.Results: Patients with TS showed higher FC in the BG, CB, DMN, and SMN and lower FC in FP and SN thanHS. Patients with OCD showed higher FC in the CB, FPN, SN, SMN than HS and higher FC in CB and FP thanTS 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, YTGSSscores 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 theirrelationship with tic severity. An increased FC in CB and FP networks characterizes OCD and distinguishes itfrom TS; this finding persisted also when comparing OCD withTS plus OCD patients, suggesting differentneural underpinnings in these two disorders.