On the treshold of disorder. Definition and course of subthreshold depression and subthreshold anxiety

PhD ceremony: Ms. J. Karsten, 12.45 uur, Academiegebouw, Broerstraat 5, Groningen

Disseration: On the treshold of disorder. Definition and course of subthreshold depression and subthreshold anxiety

Promotor(s): prof. W.A. Nolen, prof. B.W.J.H Penninx

Faculty: Medical Sciences

Subthreshold depression and subthreshold anxiety are common and associated with increased impairment, subjective suffering, and economic costs. Furthermore, individuals with subthreshold depression or subthreshold anxiety are at elevated risk for developing full-syndromal psychiatric disorders. However, no empirically based operationalization for these subthreshold disorders is available, leading to different outcomes in the literature regarding symptom features, correlates, and course. In this study, we empirically operationalized subthreshold, yet clinically significant depression and anxiety leading to functional impairment, on the criterion that mental problems must be impairing to be regarded as clinically significant (the so called “clinical significance criterion of mental disorder”). We then assessed their course over two years in terms of (1) occurrence of full-syndromal depressive and anxiety disorder and (2) extent of functional impairment. We found that clinically significant subthreshold depression and subthreshold anxiety were better defined by cut-off scores on symptom severity scales, respectively the IDS-SR30 and the BAI, than a symptom cut-off in a diagnostic interview, the CIDI. Based on these cut-off scores, subthreshold depression and subthreshold anxiety were strong predictors of full-syndromal depressive and anxiety disorders within two years, in addition to a depressive or anxiety disorder in the past. Individuals with subthreshold depression or subthreshold anxiety were still more impaired than individuals below the subthreshold cut-off two years later. Worse functioning was associated with a history of anxiety disorder, high neuroticism, low conscientiousness, a high number of traumatic events in childhood, and a high number of somatic conditions. Considerations for treatment of subthreshold disorder and prevention of full-syndromal disorders are discussed.