Research report Onset of Depression Inventory (ODI)—Assessment of the speed of onset of depressive episodes Maria Strauss n , Christian Sander, Roland Mergl, Christina Merz, Peter Sch ¨ onknecht, Ulrich Hegerl Department of Psychiatry and Psychotherapy, University of Leipzig, Semmelweisstraße 10, 04103 Leipzig, Germany article info Article history: Received 18 January 2012 Received in revised form 1 May 2012 Accepted 1 May 2012 Available online 28 July 2012 Keywords: Onset of Depression Inventory Major depression Bipolar depression Speed of onset Depressive episode abstract Background: The development of a full blown depressive episode may be very rapid, taking less than one hour, or be very slow, taking up to months. In a previous study with outpatients it was found that the majority (58%) of depressive episodes within bipolar affective disorders (BD) develop within one week whereas this is rarely the case (7.4%) in unipolar depression (UD). Apart from a replication of these findings, the present study aimed to investigate the speed of onset in patients with BD compared to UD patients with either a depressive episode (DE) or recurrent depressive disorder (RD). Methods: Speed of onset of depression was assessed using the structured patient interview ‘‘Onset of Depression Inventory’’ (ODI). In total, 24 BD patients, 42 patients with a DE and 80 patients with a RD within unipolar affective disorders were included. Results: The speed of onset of depressive episodes differed significantly between the three patient groups (Kruskal–Wallis-test: Chi 2 ¼12.493, p ¼0.002): 50% of the BD patients developed a depressive episode within a week, compared with only 16.7% of DE patients and 25.0% of RD patients. Limitations: The ODI has not yet been validated. Conclusions: The earlier finding of a faster onset of depressive episodes in BD compared to UD patients is replicated. Clinicians should consider the possibility of a hidden bipolarity in patients who develop a depressive episode within a few days. & 2012 Elsevier B.V. All rights reserved. 1. Introduction Identifying subgroups with homogeneous pathophysiological changes in patients with depressive disorders is a basic prerequi- site for studying the underlying neurobiological pathological mechanisms. One important aspect in this process is to investi- gate the onset of depressive episodes. An understanding of the onset and development of depressive episodes is promoted significantly by studies (Iacoviello et al., 2010, Lam and Wong, 1997) dealing with prodromal symptoms of depressive disorders, both unipolar (UD) and bipolar (BD). However, early recognition of whether a depressive episode occurs as part of a unipolar or bipolar affective disorder is difficult unless hypomanic or manic episodes have occurred, or been documented in case histories (Angst et al., 2005). Although 45% of patients with a bipolar disorder initially experienced a depressive episode (Goldberg et al., 2001), there are no clear distinguishing features. Nonetheless, a number of features speak for one or another diagnose. Patients with BD appear to develop atypical symptoms such as hypersomnia or hyperphagia more frequently (Mitchell et al., 2008). Another characteristic of bipolar disorders is an early age at the beginning of the first depressive episode, a relatively large number of previous depressive episodes, shorter duration of such episodes and a positive family history of BD. In contrast, many patients with major depression (MD) initially experience insomnia, reduced appetite and weight loss (Abrams and Taylor, 1980). A potentially interesting distinction between BD and MD in this context is the speed of onset of depressive episodes. Clinical observations have shown that depressive episodes develop at different speeds. The development of a full blown depressive episode can be very rapid, taking less than one hour in some patients, or be very slow, taking up to months. Surprisingly, up to now little attention has been paid to this clinical characteristic. One study, which considered the time to admission of patients suffering from affective disorders into hospitals, reported a more sudden onset of depression in patients with BD compared with patients with MD (Winokur, 1976). Another retrospective study found that 44.8% of BD patients, but only 15.9% of MD patients developed their depressive episode within less than 3 months (Gassab et al., 2002). The ‘‘Onset of Depression Inventory’’ (ODI) was developed to systematically record the speed of onset of depressive episodes (Hegerl et al., 2008a, 2008b). An ODI-based study with 158 depressed patients (mainly outpatients) showed that 58% of BD patients, but only 7.4% of patients with UD, developed one depressive episode Contents lists available at SciVerse ScienceDirect journal homepage: www.elsevier.com/locate/jad Journal of Affective Disorders 0165-0327/$ - see front matter & 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.jad.2012.05.002 n Corresponding author. Tel.: þ49 341 97 24304; fax: þ49 341 97 24509. E-mail address: maria.strauss@medizin.uni-leipzig.de (M. Strauss). Journal of Affective Disorders 142 (2012) 156–160