The finding:
This multicenter study used mixture modelling, a statistical modality used to identify candidate subtypes of mental disorders, to identify possible subtypes of trichotillomania (TTM) and excoriation (skin picking) disorder (SPD). The study investigators found that TTM could be characterized into 3 different subtypes that were generally ordered by the intensity of the urge to pull and the frequency of these behaviors as well as their association with negative emotions. For SPD, the study authors described 2 subtypes that differentiated by the intensity of urges to pick, association with negative emotions, and degree of control over the behaviors. The authors speculated, in the case of SPD, whether these were true subtypes versus different degrees of severity of the same disorder.

Strength and weaknesses:
While this is the largest study to date examining potential subtypes of body-focused repetitive behavior (BFRB) disorders, the study sample was still somewhat small to estimate mixture models. Though the study was conducted at multiple sites, including one international site, there were no data regarding ethnicity, and this was not a variable of interest in the study.

Relevance:
Improved characterization of these disorders may inform more targeted treatments. The authors highlight that the phenomenology and pathophysiology of both trichotillomania (TTM) and excoriation (skin picking) disorder (SPD) are poorly understood due to the limitations of the studies of these disorders to date. Given the generally poor response to existing treatments and frequent recurrence in these disorders, characterization may aid in forming more targeted treatments.

Type of study (EBM guide):
Cohort study