Stein et al found no evidence for caudate volume abnormalities in 7 patients with trichotillomania compared with 12 controls using magnetic resonance imaging (MRI) (putamen volumes were not assessed). However, these results were described by the authors as preliminary owing to the relatively small sample size and lack of correction for multiple comparisons. O'Sullivan et al Reference O'Sullivan, Rauch, Breiter, Grachev, Baer, Kennedy, Keuthen, Savage, Manzo, Caviness and Jenike11 reported reduced left putamen volumes in a sample of 10 patients with trichotillomania v. Reference Menzies, Chamberlain, Laird, Thelen, Sahakian and Bullmore9, Reference Menzies, Achard, Chamberlain, Fineberg, Chen, del Campo, Sahakian, Robbins and Bullmore10 neurocognitive circuits, rather than lesions within a discrete region. This is particularly relevant when considering obsessive–compulsive-spectrum disorders, which are theoretically underpinned by abnormalities in large-scale brain systems, i.e. Therefore, critically implicated regions may have been overlooked. Extant trichotillomania neuroimaging studies have all used region-of-interest approaches, rather than exploring distributed abnormalities over the whole brain. Reference Welch, Lu, Rodriguiz, Trotta, Peca, Ding, Feliciano, Chen, Adams, Luo, Dudek, Weinberg, Calakos, Wetsel and Feng8Īlthough these translational models implicate developmental abnormalities of the striatum and cortex in pathological hair-pulling, and neurobiological overlap between trichotillomania and obsessive–compulsive disorder has been suggested, there have been no whole-brain studies of the disorder with which to validate these approaches.
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Mice with genetic deletion of a postsynaptic scaffolding protein expressed in the striatum (SAP90/PSD95-associated protein) exhibit compulsive grooming behaviour leading to hair-loss and skin lesions. Reference Greer and Capecchi7 The Hoxb8 gene is expressed in multiple brain regions, including the striatum and cingulate cortex. Mice with disruption of the HoxB8 gene, which is involved in neuronal development, exhibit pathological grooming behaviour. By contrast, hair-pulling is a relatively specific behaviour that occurs across species and several promising animal models exist. It is difficult to model intrusive obsessional thoughts or complex vocal tics in animals. The lack of established treatment guidelines for trichotillomania, and lack of public/clinician awareness, facilitates recruitment of patients who are not medicated to avoid this confound. Studies of obsessive–compulsive disorder and Tourette syndrome have often been confounded by current medications. In comparison with other related conditions where compulsivity is also a prominent component, trichotillomania offers advantages in terms of neuroscientific investigation.
Reference Chamberlain, Menzies, Sahakian and Fineberg5 Reference Chamberlain, Menzies, Sahakian and Fineberg5, Reference Singer and Minzer6 There have been no brain-wide structural studies of trichotillomania, which hampers our understanding of its neurobiological profile and overlap with other obsessive–compulsive disorders. Reference Stein, Simeon, Cohen and Hollander4 Neurobiological models of these other conditions posit dysregulation of neural circuitry involved in habit formation and top-down inhibitory control, based on tiers of evidence from neuroimaging and elsewhere.
Reference Christenson, Pyle and Mitchell3 Trichotillomania has phenomenological overlap with obsessive–compulsive disorder and Tourette syndrome, and consequently represents a candidate member of the obsessive–compulsive spectrum. Based on a survey conducted in 2500 college students, lifetime prevalence has been estimated to be 0.6–2.5%.
Reference Cohen, Stein, Simeon, Spadaccini, Rosen, Aronowitz and Hollander2 There have been no population-wide epidemiological studies of the condition. Reference Cohen, Stein, Simeon, Spadaccini, Rosen, Aronowitz and Hollander2 Peak age at onset is 12–13 years, and hair-pulling most commonly affects the scalp and eyelashes/eyebrows. 1 Unfortunately, the majority of sufferers have never been diagnosed and have never received treatment.
Trichotillomania is an impulse control disorder characterised by repetitive hair-pulling that leads to noticeable hair loss and functional impairment (DSM–IV).
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