Duration of illness and cortical thickness in trichotillomania: Preliminary evidence for illness change over time
Introduction
Trichotillomania is a psychiatric condition characterized by recurrent pulling out of one's own hair, leading to hair loss (APA, 2013). Brain imaging studies have suggested that the pathophysiology of trichotillomania is linked to abnormalities in both cortical regions (associated with top-down control and habit suppression) and sub-cortical neural regions (such as the dorsal striatum involved in habit generation) (Chamberlain et al., 2009, Chamberlain et al., 2010, Chamberlain et al., 2018; Grant et al., 2018; Isobe et al., 2018; Olduag et al., 2014; Slikboer et al., 2018; White et al., 2013). The findings from imaging studies in trichotillomania, however, have not always shown consistent findings (see Roos et al., 2013 no differences in trichotillomania compared to controls in white matter tracts of the fronto-striatal-thalamic pathway), and this raises the question as to whether trichotillomania is a heterogeneous disorder. Previous neuroimaging studies have examined brain abnormalities in individuals with current trichotillomania but have not examined the impact of symptom chronicity (duration of illness or clinical stage) on brain structure in patients – an issue that could be important in better understanding the heterogeneity of a disorder. Studies with other disorders have shown the importance of duration of illness/clinical staging in their presentation. In the case of substance use disorders, studies have suggested that longer duration of illness is correlated with more cognitive deficits (e.g., response inhibition and cognitive flexibility Laloyaux et al., 2012; Monterosso et al., 2005). Studies have further found that longer duration of illness may be associated with structural abnormalities such as gray and white matter volumes reductions, as well as decreased brain activation, in substance use disorders (Bjork et al., 2003; Ersche et al., 2011; Sjoerds et al., 2014), bipolar disorder (in the area of the hippocampus and amygdala; Gildengers et al., 2014), body dysmorphic disorder (right orbitofrontal cortex volumes; Buchanan et al., 2014), and obsessive-compulsive disorder (hippocampus and amygdala; Atmaca et al., 2008).
Although clinical stage seems to be an important issue in understanding psychiatric disorders, no study has specifically investigated how this variable might affect our understanding of neuroimaging results in trichotillomania. Therefore, our objective in this study was to investigate structural neuroimaging results associated with different durations of illness in a large pooled sample of adults with trichotillomania. Toward that end, the current study obtained available MRI scans (along with select demographic and clinical information) from research groups that have published peer-reviewed data papers of trichotillomania and examined cortical thickness and sub-cortical structure volumes. We hypothesized that longer duration of illness in trichotillomania would be associated with cortical thickness abnormalities in frontal cortical sectors coupled with excess volume of the dorsal striatum (putamen/caudate).
Section snippets
Participants
All structural MRI studies regarding trichotillomania were identified via PubMed in May 2019. We contacted the authors of these publications and invited them to contribute de-identified MRI scans from published studies. Written informed consent was obtained from all participants, and the original studies each received Institutional Review Board approvals. Conventional cortical data for many in the current sample were reported previously and the MRI dataset obtained here was largely overlapping
Results
The study sample comprised 50 adults with trichotillomania (92% female; mean [SD] age = 34.2 [12.3] years) who also had data regarding the duration of their illness. The mean total MGH-HPS severity score was 15.1 [4.4], consistent with, on average, mild-moderate illness; and the mean duration of illness was 21.5 [13.0] years. Of 44 people for whom education level data were available, 29 (58%) had graduate/higher degree level education, six (12%) had college/lower degree level education, and
Discussion
This study supports the hypothesis that longer duration of illness is associated with reduced cortical thickness in the left rostral middle frontal cortex and bilaterally in the superior frontal cortices, in trichotillomania. As such, this study is the first to show that the illness of trichotillomania is associated with potentially progressive biological changes over time. If this finding is supported by prospective studies, it could have important implications for treatment (i.e. would
Author Contribution
All authors contributed to the design of the study, carrying it the study, analyzing the data and writing the article.
Conflict of interest
Dr. Grant has received research grants from TLC Foundation, and Takeda Pharmaceuticals. Dr. Grant receives yearly compensation from Springer Publishing for acting as Editor-in-Chief of the Journal of Gambling Studies and has received royalties from Oxford University Press, American Psychiatric Publishing, Inc., Norton Press, and McGraw Hill. Dr. Chamberlain's time on this study was supported by a Wellcome Trust Clinical Fellowship (110049/Z/15/Z). Dr. Chamberlain consults for Cambridge
Acknowledgments
None.
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