The differential diagnosis will include evaluation for alopecia areata, iron deficiency, hypothyroidism, tinea capitis, traction alopecia, alopecia mucinosa, thallium poisoning, and loose anagen syndrome. In trichotillomania, a hair pull test is negative.A biopsy can be performed and may be helpful; it reveals traumatized hair follicles with perifollicular hemorrhage, fragmented hair in the dermis, empty follicles, and deformed hair shafts. Multiple catagen hairs are typically seen. An alternative technique to biopsy, particularly for children, is to shave a part of the involved area and observe for regrowth of normal hairs. Classification
Trichotillomania is defined as a self-induced and recurrent loss of hair. It includes the criterion of an increasing sense of tension before pulling the hair and gratification or relief when pulling the hair. However, some people with trichotillomania do not endorse the inclusion of "rising tension and subsequent pleasure, gratification, or relief" as part of the criteria because many individuals with trichotillomania may not realize they are pulling their hair, and patients presenting for diagnosis may deny the criteria for tension prior to hair pulling or a sense of gratification after hair is pulled.Trichotillomania may lie on the obsessive-compulsive spectrum, also encompassing obsessive-compulsive disorder (OCD), body dysmorphic disorder (BDD), nail biting (onychophagia) and skin picking (dermatillomania), tic disorders and eating disorders. These conditions may share clinical features, genetic contributions, and possibly treatment response; however, differences between trichotillomania and OCD are present in symptoms, neural function and cognitive profile.
Trichotillomania has a high overlap with post traumatic stress disorder, and some cases of trichotillomania may be triggered by stress. Another school of thought emphasizes hair pulling as addictive or negatively reinforcing, as it is associated with rising tension beforehand and relief afterward. A neurocognitive model — the notion that the basal ganglia play a role in habit formation and that the frontal lobes are critical for normally suppressing or inhibiting such habits — sees trichotillomania as a habit disorder.Abnormalities in the caudate nucleus are noted in OCD, but there is no evidence to support that these abnormalities can also be linked to trichotillomania. One study has shown that individuals with trichotillomania have decreased cerebellar volume. These findings suggest some differences between OCD and trichotillomania. There is a lack of structural MRI studies on trichotillomania. In several MRI studies that have been conducted, it has been found that people with trichotillomania have more gray matter in their brains than those who do not have the disorder.It is likely that multiple genes confer vulnerability to trichotillomania. One study identified mutations in the SLITRK1 gene. Diagnosis
Patients may be ashamed or actively attempt to disguise their symptoms. This can make diagnosis difficult as symptoms are not always immediately obvious, or have been deliberately hidden to avoid disclosure. If the patient admits to hair pulling, diagnosis is not difficult; if patients deny hair pulling, a differential diagnosis must be pursued.