Comparing the Illness Anxiety Disorder With Obsessive-Compulsive Disorder and Generalized Anxiety Disorder Based on the Cognitive Transdiagnostic Constructs

Transdiagnostic models are among the most prominent approaches in psychopathology that emphasize basic and underlying processes in mental disorders. Perfectionism, intolerance of uncertainty, responsibility, and anxiety sensitivity are cognitive constructs that have been introduced as transdiagnostic factors seen in many psychological disorders. Illness anxiety disorder is one of the new disorders defined in the Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition (DSM–5) under the diagnostic category of "somatic symptoms and related disorders." Anxiety disorder is nosologically similar to obsessive–compulsive disorder and generalized anxiety disorder. This nosological overlap has led some theorists to classify illness anxiety disorder in the diagnostic category of "obsessive–compulsive and related disorders," while others have suggested that illness anxiety disorder belongs to the category of anxiety disorders. Because of these disagreements, the present study aimed to compare illness anxiety disorder with obsessive–compulsive disorder and generalized anxiety disorder based on the cognitive transdiagnostic constructs of anxiety sensitivity, perfectionism, responsibility, and intolerance of uncertainty.

The method of this research was casual comparative. The statistical population of this study consisted of all patients with anxiety disorder, obsessive–compulsive disorder, or generalized anxiety disorder who were referred to the clinics of Hafez and Ibn Sina hospitals in Shiraz City, Iran, in 2019. The sample consisted of 15 patients with illness anxiety disorder, 15 with obsessive–compulsive disorder, and 15 with generalized anxiety disorder. These patients were selected through a non–random and purposeful sampling method. The inclusion criteria were aged 18 – 60 years, literate, with a definitive diagnosis of the disorder by a psychiatrist and using screening tools. The exclusion criteria included a lifetime diagnosis of psychotic disorders, substance use disorders, organic brain diseases or mental disorders due to physical problems, and a physical illness that justifies the patient's physical complaints. Also, to reduce overlap between diagnostic groups, patients in each group who overlapped with other groups were excluded from the study. The study tools included the Perfectionism Inventory (Hill et al., 2004), Responsibility Attitude Scale (Salkovskis et al., 2002), Intolerance of Uncertainty Scale (Freeston et al., 1994), and Anxiety Sensitivity Index–Revised (Taylor & Cox, 1998). Data analysis was performed using descriptive statistics (mean and standard deviation) and inferential statistics (univariate analysis of variance, the Chi–square, multivariate analysis of variance, and LSD post hoc test) in SPSS software version 26. The significance level of all tests was considered 0.05.

The findings of multivariate analysis of variance (MANOVA) showed no significant differences between the three groups of illness anxiety disorder, obsessive–compulsive disorder, and generalized anxiety disorder regarding the constructs of intolerance of uncertainty (p=0.757), perfectionism (p=0.835), and responsibility (p=0.616). However, the difference in anxiety sensitivity construct between the three groups was significant (p<0.001). Besides, the results of post hoc tests demonstrated that the mean scores of anxiety sensitivity in the illness anxiety disorder group were significantly higher than that in the groups of obsessive–compulsive disorder (p<0.001) and generalized anxiety disorder (p<0.001).

According to the research findings, the constructs of perfectionism, responsibility, and intolerance of uncertainty are common cognitive constructs in illness anxiety disorder, obsessive–compulsive disorder, and generalized anxiety disorder. However, people with illness anxiety disorder suffer from significantly higher levels of anxiety sensitivity.