Systematic Review of Published Primary Studies of Neuropsychology and Neuroimaging in Trichotillomania.

Objectives: Existing models of trichotillomania (TTM; hair pulling disorder) rely heavily on a biological predisposition or biological pathogenesis of the disorder, but fail to capture the specific neuropsychological mechanisms involved. The present systematic review aims to scope existing neuropsychological studies of TTM to explore gaps in current models.

Methods: A systematic literature search was conducted to detect all published primary studies using neuropsychological and neuroimaging measures in a cohort of individuals experiencing TTM. Studies addressing neuropsychological function were divided into domains. Findings from imaging studies were considered within brain regions and across methodology.

Results: Thirty studies with a combined 591 participants with TTM, 372 healthy controls and 225 participants in other types of control group were included. Sixteen studies investigated neuropsychological parameters, and 14 studies pursued neuroimaging technologies. Available studies that used neuropsychological assessments and reported a statistically significant difference between those with TTM and controls ranged in effect size from 0.25 to 1.58. All domains except verbal ability and visual ability reported a deficit. In neuroimaging studies, several structural and functional brain changes were reported that might be of significance to TTM. Only tentative conclusions can be made due to the use of multiple methodologies across studies, a major limitation to meaningful interpretations.

Conclusions: Positive neuropsychological and neuroimaging results require replication, preferably with multi-site studies using standardized methodology. Increased standardized testing and analyses across the literature, as a whole, would improve the utility and interpretability of knowledge in this field. (JINS, 2018, 24, 188-205).