White matter alterations in drug-naïve children with Tourette syndrome and obsessive-compulsive disorder

Tourette syndrome (TS) and early-onset obsessive-compulsive disorder (OCD)are frequently associated and conceptualized as distinct phenotypes of acommon disease spectrum. However, the nature of their relationship is stilllargely unknown on a pathophysiological level. In this study, early structuralwhite matter (WM) changes investigated through diffusion tensor imaging(DTI) were compared across four groups of drug-naïve children: TS-pure (n= 16), TS+OCD (n = 14), OCD (n = 10), and 11 age-matched controls. Weanalyzed five WM tracts of interest, i.e., cortico-spinal tract (CST), anteriorthalamic radiations (ATR), inferior longitudinal fasciculus (ILF), corpus callosum(CC), and cingulum and evaluated correlations of DTI changes to symptomseverity. Compared to controls, TS-pure and TS+OCD showed a comparablepattern of increased fractional anisotropy (FA) in CST, ATR, ILF and CC, withFA changes displaying negative correlation to tic severity. Conversely, inOCD, FA decreased in all WM tracts (except for the cingulum) compared tocontrols and negatively correlated to symptoms. We demonstrate differentearly WM microstructural alterations in children with TS-pure/TS+OCD asopposed to OCD. Our findings support the conceptualization of TS+OCD asa subtype of TS while suggesting that OCD is characterized by independentpathophysiological mechanisms affecting WM development.