What is the role of brain volume in the pathogenesis of Tourette syndrome (TS) and other tic disorders?

Updated: May 30, 2019
  • Author: William C Robertson, Jr, MD; Chief Editor: Stephen L Nelson, Jr, MD, PhD, FAACPDM, FAAN, FAAP  more...
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Answer

Standard neuroimaging studies in TS are unremarkable. However, volumetric MRI has suggested that the normal asymmetry of the basal ganglia is absent.

The largest study of regional brain volumes to date, which involved more than 150 individuals with TS and a similar number of comparison children and adults, showed that subjects with TS had large dorsal prefrontal and parieto-occipital regions and smaller inferior occipital volumes. [69, 70] Symptom severity was best correlated with volume in the orbitofrontal, midtemporal, and parieto-occipital cortex.

TS patients were found to have significantly reduced caudate volumes. [70, 71] The importance of this finding is highlighted by the fact that, on prospective follow-up of patients who had MRI volumetry, smaller caudate volume in childhood correlated significantly with severity of tics, obsessions, and compulsions an average of 7.5 years later. [72]

Another study showed that patients with TS had small right frontal lobes, large left frontal lobes, and more frontal lobe white matter compared with healthy control subjects. [73] Other investigators also found increased frontal white matter. [74]

Two prior studies had selectively examined basal ganglia volumes and had found slightly smaller left putamen volume and a diminution of the normal asymmetry of basal ganglia volume. [69] These findings were not replicated when more- and less-affected twins with TS were compared. [75]

One MRI study revealed abnormal T2 relaxation time in the putamen and caudate nuclei. [76] One case report described a child with a sudden onset of stereotyped behaviors after a streptococcal infection; this child had basal ganglia volumes larger than those of age-matched controls during the acute illness and smaller volumes months later. [77]

Some consistencies arise from these studies. These include decreased caudate volume and, possibly, increased prefrontal white matter and dorsolateral prefrontal gray matter volumes. In one volumetric study, abnormal basal ganglia volumes in a group of patients with TS were entirely attributable to comorbid attention deficit hyperactivity disorder (ADHD). [78]

Similar results were reported from a study of regional brain volumes in relation to streptococcal antibody titers in TS. [79] In other studies, however, the effects of OCD or ADHD were examined and did not explain all of the imaging findings.

The implication is that at a minimum, careful clinical assessment, including information about OCD or ADHD symptoms, is required when the results of any new neuroimaging study are interpreted in individuals with TS. Hopefully, structural imaging will eventually identify a specific anatomic shape that will assist in the identification of responsible genes.


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