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There is clinical overlap between skin picking disorder (SPD) and body dysmorphic disorder (BDD), but little research has examined clinical and cognitive correlates of the two disorders when they co-occur. Of 55 participants with SPD recruited for a neurocognitive study and two pharmacological studies, 16 (29.1%) had co-occurring BDD. SPD participants with and without BDD were compared to each other and to 40 healthy volunteers on measures of symptom severity, social functioning, and cognitive assessments using the Stop-signal task (assessing response impulsivity) and the Intra-dimensional/Extra-dimensional Set Shift task (assessing cognitive flexibility). Individuals with SPD and BDD exhibited significantly worse picking, significantly worse overall psychosocial functioning, and significantly greater dysfunction on aspects of cognitive flexibility. These results indicate that when SPD co-occurs with BDD unique clinical and cognitive aspects of SPD may be more pronounced. Future work should explore possible subgroups in SPD and whether these predict different treatment outcomes.

Skin picking disorder (SPD) is clinically defined in the DSM-5 as the repetitive or compulsive picking of skin to the point of causing tissue damage (American Psychiatric Association, 2013). Many individuals with SPD report that the behavior began with the onset of a dermatological condition such as acne (Wilhelm et al., 1999), but the picking continues even after the dermatological condition clears. Although the face is the most commonly reported site of picking, other areas, such as the hands, arms, and legs are also common targets. While most individuals with SPD pick at areas they can physically reach with their fingernails, they also report using a variety of utensils such as tweezers and pins to pick (Grant, Odlaug, & Kim, 2007). Individuals with SPD spend a significant amount of time picking their skin, with a mean of 2.8 hours each day spent resisting the urge to pick or picking (Flessner & Woods, 2006). The picking often leads to problems with self-esteem (Odlaug & Grant, 2010). Although SPD is now a recognized mental illness, skin picking may also be a symptom of other psychiatric disorders. One such disorder is body dysmorphic disorder (BDD), characterized by obsessions about and preoccupation with perceived defects in physical appearance (American Psychiatric Association, 2013). Individuals with BDD may pick their skin in attempts to improve the appearance of perceived skin flaws. In fact, some type of skin picking behavior occurs in between 26 and 45% of patients with BDD (Grant, Menard, & Phillips, 2006). Conversely, an early study found that 11 (32%) of 34 SPD participants also met diagnostic criteria for BDD (Arnold et al., 1998). Thus, disproportionate obsessions over perceived skin problems and compulsive picking can create a complex diagnostic picture (for example, whether the symptoms indicate one diagnosis or the other, or a comorbidity). Although there appears to be clinical overlap between SPD and BDD, individuals with BDD pick at their skin to try to improve their appearance, whereas most individuals with SPD do not pick their skin because of their appearance and therefore would not meet criteria for BDD. It is possible, however, that a person may have co-occurring SPD and BDD. For example, a person may pick at their face to improve appearance and yet also pick at their legs in an automatic fashion with no obsessive thinking about the appearance of their legs. Because the use of a clinical assessment to separate SPD from BDD often results in a confused diagnostic picture, neurocognitive assessments may allow for a more thorough examination of possible subtypes within SPD and shared pathophysiology between SPD and BDD. The repetitive physical symptoms of SPD suggest underlying dysfunction of motor inhibitory control processes. Similarly, the repetitive mirror checking and picking to improve appearance often seen in BDD may also suggest problems with motor inhibition. Motor impulsivity is classically assessed using tasks that require individuals to make simple motor responses on some computer trials but not others. Response inhibition as a cognitive function is dependent on neural circuitry that includes the right inferior frontal gyrus (Aron, Fletcher, Bullmore, Sahakian, & Robbins, 2003). Data are conflicting, however, in SPD with one study using a stop-signal task indicating impaired stop-signal inhibitory control in patients with SPD compared to healthy volunteers and intact cognitive flexibility (Odlaug, Chamberlain, & Grant, 2010) while a later study found no motor inhibitory deficits in SPD versus controls (Snorrason, Smári, & Ólafsson, 2011). Cognitive tasks studied in SPD have not been similarly performed in individuals with SPD and co-occurring BDD, and this comorbidity may explain some of the conflicting results seen in SPD studies. Scant research has focused on the neurocognition of BDD. One study found that participants with BDD exhibited deficits in cognitive flexibility (Jefferies, Laws, & Fineberg, 2010). Another small study using the Rey-Osterrieth Complex Figure Test (a task that evaluates visuospatial abilities, memory, attention, planning, and working memory), however, found that individuals with BDD alone (n = 17) exhibited deficits in organizational strategies compared to controls ( Deckersbach et al., 2000). Other research suggests that individuals with BDD may have abnormalities in visual processing ( Feusner et al., 2010 and Yaryura-Tobias et al., 2002). Cognitive testing of motor inhibitory deficits in BDD, however, is currently lacking. Although SPD and BDD have clinical overlap, the neurocognitive research of SPD and BDD has to date failed to provide clarity regarding the differences or similarities of these disorders. This may be because SPD comprises a heterogeneous illness, and the co-occurrence of SPD with BDD may be one important subtype of SPD. To help clarify the heterogeneity of SPD, we have chosen objective neurocognitive tasks hypothesized to reflect impairments in motor inhibition and cognitive flexibility which are dependent upon integrity of frontal–striatal circuitry. Thus, the aims of the current study were to examine the previously unstudied questions concerning clinical and cognitive differences between individuals with SPD and those with SPD co-occurring with BDD. In terms of clinical variables, we hypothesized that SPD co-occurring with BDD would result in more severe skin picking, greater psychosocial dysfunction and worse quality of life. In terms of cognitive variables, we hypothesized that the co-occurrence of SPD and BDD would result in greater motor impulsivity as indexed by the stop-signal paradigm, but intact set-shifting.