Hippocampal Volume in Provisional Tic Disorder Predicts Tic Severity at 12-Month Follow-up.

Kevin Black,Emily Bihun,Jonathan Koller,Bridget O’Reilly,Soyoung Kim,Bradley Schlaggar,Carolina D’Andrea,Deanna Greene

doi:10.3390/jcm9061715

Abstract

Previous studies have investigated differences in the volumes of subcortical structures (e.g., caudate nucleus, putamen, thalamus, amygdala, and hippocampus) between individuals with and without Tourette syndrome (TS), as well as the relationships between these volumes and tic symptom severity. These volumes may also predict clinical outcome in Provisional Tic Disorder (PTD), but that hypothesis has never been tested. This study aimed to examine whether the volumes of subcortical structures measured shortly after tic onset can predict tic symptom severity at one-year post-tic onset, when TS can first be diagnosed. We obtained T1-weighted structural MRI scans from 41 children with PTD (25 with prospective motion correction (vNavs)) whose tics had begun less than 9 months (mean 4.04 months) prior to the first study visit (baseline). We re-examined them at the 12-month anniversary of their first tic (follow-up), assessing tic severity using the Yale Global Tic Severity Scale. We quantified the volumes of subcortical structures using volBrain software. Baseline hippocampal volume was correlated with tic severity at the 12-month follow-up, with a larger hippocampus at baseline predicting worse tic severity at follow-up. The volumes of other subcortical structures did not significantly predict tic severity at follow-up. Hippocampal volume may be an important marker in predicting prognosis in Provisional Tic Disorder.

Highlights

Tic disorders are neurodevelopmental disorders defined by the presence of tics: sudden, rapid, recurrent, non-rhythmic movements or vocalizations [1]
Among 64 image quality metrics of MRIQC, we found that the average signal-to-noise ratio (SNR) of gray matter, white matter, and cerebrospinal fluid (CSF) (hereafter “SNR”) calculated using the within-tissue variance was highly correlated with subjective rating by visual inspection following standardized criteria [25]
Cross-sectional analyses to examine the relationship between the volumes of subcortical structures and the total tic score within the baseline session revealed no significant association in any subcortical structure volumes (p ≥ 0.25; Figure 1, second row)

Summary

Introduction

Tic disorders are neurodevelopmental disorders defined by the presence of tics: sudden, rapid, recurrent, non-rhythmic movements or vocalizations [1]. Studies in search of tic biomarkers have primarily compared people with TS to a control sample, identifying significant differences in neurophysiological measures, such as brain anatomy or function. Findings from such studies cannot disentangle whether the differences are due to an underlying cause of tics or secondary, compensatory changes that occur with the prolonged presence of tics. The goal of the current study was to identify volumetric Magnetic Resonance Imaging (MRI) biomarkers that can predict one-year tic outcome in children with recent-onset tics (i.e., tic duration < 9 months).

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