(PS2-25) Illness Anxiety Disorder and Somatic Symptom Disorder: Distinct Diagnoses or One and the Same?

Background: Severe health anxiety affects 500,000 Australians each year and is characterized by excessive worry about the existence or development of serious medical conditions (Fink et al., 2010; Sunderland et al., 2013). In the DSM-5, severe health anxiety is captured by two disorders, Illness anxiety disorder (IAD) and Somatic Symptoms Disorder (SSD). While previous research in treatment-seeking patients found limited distinctive characteristics between the disorders, variability in severity has been reported, with SSD being more severe (Axelsson et al., 2023; Bailer et al., 2016; Newby et al., 2017). However, more research is needed to compare IAD and SSD across different samples. To address this gap, we sought to examine differences between IAD and SSD in a community sample.

Methods: We recruited 118 participants from the community (M age = 41 years, 84% female, 70% Caucasian, 67% completed a university degree, 56% currently receiving treatment for mental illness). Participants were administered the ADIS-5 diagnostic interview to assess IAD, SSD and comorbid and differential diagnoses. Participants completed an online survey, including self-report assessment measures of health anxiety severity, onset and course, other mental health symptoms (e.g., generalized anxiety and depression), and health service use. Independent t-tests and chi square analyses were used to compare means between groups on demographic and clinical characteristics, and health service utilization.

Results: The average age of health anxiety onset was 24 years (range: 4-65 years). Over half (55%) experienced a chronic and episodic course, with most (84%) fearing multiple illnesses. Participants with SSD showed significantly greater health anxiety severity, depression severity, generalized anxiety, lower quality of life, more chronic health conditions, and used significantly more healthcare services than participants with IAD (all ps >.05). No significant differences between the groups were found in terms of demographic characteristics, illness onset and course, and mental health diagnostic comorbidities.

Conclusion: These findings provide further support that the distinction between IAD and SSD is primarily a matter of severity, raising questions about the clinical utility of having two separate diagnoses for health anxious individuals. For clinicians delivering cognitive-behavioral therapies, this finding suggests that when assessing individuals with health anxiety, those diagnosed with SSD are likely to exhibit more severe symptoms compared to those diagnosed with IAD but are unlikely to differ on other characteristics. There are several limitations associated with this study, including the cross-sectional nature of the data, and that the sample was mostly female, Caucasian, and well-educated. These characteristics limit the generalizability of these findings to other groups.