Background Though the phenotype of anxiety about medical illness has long been recognized, there continues to be debate as to whether it is a distinct psychiatric disorder and, if so, to which diagnostic category it belongs. Our objective was to investigate the pattern of psychiatric co-morbidity in hypochondriasis and to assess the relationship of health anxiety to anxiety, depressive, and somatoform disorders. Methods Data were collected as part of a clinical trial on treatment methods for hypochondriasis. 194 participants meeting criteria for DSM-IV hypochondriasis were assessed by sociodemographic variables, results of structured diagnostic interviews, and validated instruments for assessing various symptom dimensions of psychopathology. Results The majority of individuals with hypochondriasis had co-morbid psychiatric illness; the mean number of co-morbid diagnoses was 1.4, and 35.1% had hypochondriasis as their only diagnosis. Participants were more likely to have only co-morbid anxiety disorders than only co-morbid depressive or somatoform disorders. Multiple regression analysis of continuous measures of symptoms revealed the strongest correlation of health anxiety with anxiety symptoms, and a weaker correlation with somatoform symptoms; in multiple regression analysis, there was no correlation between health anxiety and depressive symptoms. Conclusion Our findings suggest that the entity of health anxiety (Hypochondriasis in DSM-IV, Illness Anxiety Disorder in DSM-5) is a clinical syndrome distinct from other psychiatric disorders. Analysis of co-morbidity patterns and continuous measures of symptoms suggest its appropriate classification is with anxiety rather than somatoform or mood disorders.

Illness anxiety disorder is a primary disorder of anxiety about having or developing a serious illness. The core feature is the cycle of worry and reassurance seeking regarding health, as opposed to a focus on relief of distress caused by somatic symptoms (as in Somatic Symptom Disorder). Clinically significant health anxiety is common, with estimates ranging up to 13% in the general adult population. There are evidence-based treatments, including psychopharmacology and cognitive behavioral therapy, that can significantly alleviate symptoms. An understanding of the core psychopathology and clinical features of illness anxiety disorder is essential to fostering a working alliance with patients with health anxiety, as is the maintenance of an empathic, curious, and nonjudgmental stance toward their anxiety. Collaboration between medical providers is essential to avoid the pitfalls of excess testing and medical treatment.