Research reportSeasonal and nonseasonal depression: how do they differ?: Symptom profile, clinical and family history in a general population sample
Introduction
Seasonal affective disorder (SAD) has generated much research interest since being first described in 1984 (Rosenthal et al., 1984). In DSM-IV, (American Psychiatric Association, 1994), SAD is categorised as a ‘seasonal pattern’ that may be applied to bipolar disorder (type I or II) or major depressive disorder, recurrent. DSM-IV criteria for a seasonal pattern require: regular onset and remission of depressive symptoms during particular times of the year, two major depressive episodes in the last 2 years with no intervening nonseasonal episodes and seasonal episodes outnumbering nonseasonal episodes over the individual’s lifetime. ICD-10 criteria (World Health Organisation, 1994) require that at least three consecutive annual episodes of depression occur, with onset and remission being within a specific 90-day period. As such, seasonal depression is diagnostically distinguished from nonseasonal depression solely by the temporal pattern of depressive episodes, and not by any specific presenting symptoms.
SAD is, however, known to be characterised by a number of atypical depressive symptoms such as increased appetite, weight gain and hypersomnia (Rosenthal et al., 1984; Rosenthal et al., 1987b; Thompson and Isaacs, 1988). A small number of studies have now compared the symptom profiles and clinical and family history patterns of patients with seasonal and nonseasonal depression (Garvey et al., 1988; Allen et al., 1993; Thalen et al., 1995; Tam et al., 1997). Broadly, this research has indicated that seasonal depression may be distinguished from nonseasonal depression by the presence of these telling atypical symptoms. Furthermore, seasonal and nonseasonal depressives appear to possess contrasting clinical histories, with seasonal depressives tending to receive less psychiatric and pharmacological intervention than nonseasonal depressives.
Research to date comparing the characteristics of patients with seasonal and nonseasonal depression has been conducted in secondary or tertiary care settings. This study aimed to compare the symptom profiles, clinical history and family history of seasonal and nonseasonal depressives identified in an equivalent manner within a general population sample. Evidence that SAD possesses a discrete symptom profile compared to nonseasonal depression could help clinicians distinguish between seasonal and nonseasonal depression in primary care settings, and provide further evidence that SAD is a distinct subtype of depression.
Section snippets
Methods
Participants were recruited as part of the Outcomes of Depression International Network (ODIN) project. The ODIN project is an international study designed to assess the prevalence of depressive disorders and risk factors for depression in urban and rural areas within the European Community (Dowrick et al., 1998; Dowrick et al., 1999). Additional work examining the prevalence of SAD was conducted in conjunction with standard ODIN methodology at the project’s North Wales site in the United
Results
One thousand nine hundred and ninety nine people were sent screening questionnaires, with a 63% (n=1,250) response rate being obtained. Younger people were significantly less likely to respond to the screening questionnaire than older people (t=5.7, df=1,440, P<0.001), the mean age of non-responders being 40 and that of responders being 43. Men were significantly less likely to respond than women, with a response rate of 58.6% compared to 67.4% (χ2=16.5, P<0.001).
Sixty-six respondents (5.3%)
Discussion
The main findings of this study suggest that SAD is a relatively mild and distinct variant of depression in this general population sample. SAD appears to result in lower occupational and cognitive impairment and psychiatric intervention than its nonseasonal counterpart. The symptoms of hopelessness and weight loss may be helpful as predictive symptoms in distinguishing between episodes of seasonal and nonseasonal depression.
A small number of studies have previously compared the attributes of
Conclusions
The finding that SAD is a relatively mild form of depression in the general population fits with our clinical experience of the condition in primary care populations. This is not to say, however, that we should not continue to strive to improve the detection and treatment of SAD in primary care settings. SAD remains a common disorder, and potentially results in significant personal and societal impairment. Furthermore, an efficacious treatment for SAD has been identified in the form of light
Acknowledgements
With thanks to Victoria Higgin for secretarial support. We are indebted to the practice staff and participants at the surgeries involved in the ODIN project. The North Wales arm of the ODIN project received financial support from the European Commission Biomed 2 Programme (Contract BMH-4-CT96-1681) and the Wales Office of Research and Development (Contract RC092).
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