North Wales Section of the Department of General Practice, University of Wales College of Medicine
North Wales Section of the Department of General Practice, University of Wales College of Medicine
Department of Primary Care, University of Liverpool
Department of Psychiatry, University of Liverpool
Correspondence: Erin E. Michalak, North Wales Section of the Department of General Practice, Gwenfro Building, Wrexham Technology Park, Wrexham LL13 7YP
Declaration of interest Funded by 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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ABSTRACT |
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Aims To determine the prevalence, detection and current treatment of SAD within a general population sample.
Method The study was conducted in conjunction with the Outcomes of Depression International Network (ODIN) project, a large European study of depression. At the North Wales arm of the project, 1999 adults were randomly selected from a health authority database and screened by post for SAD with the Seasonal Patterns Assessment Questionnaire (SPAQ). Those scoring above cut-off were offered diagnostic interview, after which diagnosis of SAD according to DSM-IV criteria could be made.
Results The prevalence rate of SAD was calculated to be 2.4% (95% CII.4-1.3). The majority of identified cases had not previously received a diagnosis of SAD from their general practitioner, although over half had been diagnosed with other forms of depression and had been prescribed antidepressant medication.
Conclusions Although SAD was found to be common in this general population sample it appeared to be largely underdiagnosed and/or misdiagnosed.
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INTRODUCTION |
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METHOD |
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Sample frame
The sample was made up of adults aged between 18 and 64 years registered on
the North Wales Health Authority's general practice database residing within
the former Glyndwr council district in North Wales.
Case finding
A two-phase sampling method was adopted as a research strategy for the ODIN
project (Pickles & Dunn,
1995) using a self-rating postal survey to identify potential
cases of depressive disorder, followed by structured diagnostic interview and
more detailed questionnaires with those participants scoring above
threshold.
In North Wales, the initial screening package also included a sub-scale of the SPAQ from which a global seasonality score (GSS) for a given individual was derived. This score ranges from 0 to 24, and indicates the degree of change an individual experiences between the seasons in their sleep, mood, weight, appetite, energy and social activity, and requires that the individual describe whether these changes represent a mild, moderate, marked, severe or disabling problem for them. Beck Depression Inventory (BDI; Beck et al, 1961) scores, short measures of social support, recent life events and basic demographic questions were also incorporated into the screening package in the normal course of the ODIN project. The bulk of the package was available in both English and Welsh, and non-responders were contacted up to three times by letter and telephone to encourage participation.
The second diagnostic interview stage of assessment was conducted with all consenting participants who possessed: (a) a GSS of 11 or more with seasonal changes amounting to at least a moderate problem; and (b) a randomly selected 5% sample. For the GSS sample, interviews were conducted during the winter of 1997-1998 by a trained research worker (E.E.M.) according to the revised version of the Structured Interview Guide for the Hamilton Depression Rating Scale Seasonal Affective Disorder Version (SIGHSAD; Williams et al, 1992). Diagnostic criteria utilised were a minimum score of 15 on the Hamilton Rating Scale for Depression (HRSD; Hamilton, 1960), with a score of at least six on the supplementary atypical item scale. Diagnosed cases of SAD were those participants who fulfilled SPAQ, SIGHSAD and DSMIV (American Psychiatric Association, 1994) criteria. Additional questionnaires and data concerning participants' previous diagnoses of depression, SAD and treatment history were also obtained at the time of interview.
Weighted prevalence estimates, taking into account the two-phase sampling strategy, were obtained using the svyprop and logit commands of STATA as described in Dunn (2000).
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RESULTS |
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Sixty-six respondents (5.3%) screened positive for SAD according to SPAQ criteria. Fifty-five (83%) of this sample agreed to undergo diagnostic interview and 25 were diagnosed with SAD according to the outlined criteria. The statistical package STATA-5 (StataCorp, 1997) was used to calculate a prevalence rate of 2.4% (s.e.= 0.7, 95% CI 1.4-4.3) for SAD (see Fig. 1).
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Diagnosis and treatment history data showed that the majority of identified cases had not previously received a diagnosis of SAD or undergone light therapy, although they had frequently received diagnoses of other forms of depression and had taken antidepressant medication (see Table 1).
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DISCUSSION |
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Diagnostic implications
Although SAD does appear to occur fairly widely in the general population,
general practitioners are likely to underdiagnose the disorder for a number of
reasons. It is thought that general practitioners correctly identify
depression in around half of the cases they are presented with
(Freeling et al,
1985). Moves such as the Defeat Depression Campaign (Priest et
al, 1991) have concentrated upon further improving the identification and
treatment of depression in primary care. However, it may be particularly
difficult for general practitioners to recognise forms of depression
characterised by somatic symptoms such as weight gain, fatigue and
hypersomnia, all of which typify SAD
(Goldberg & Bridges,
1988). Of the 25 patients diagnosed with SAD in the present study,
only one had previously received a diagnosis of SAD from their general
practitioner, although over half had received diagnoses of other forms of
depression and had been prescribed antidepressants. SAD does appear to be
underdiagnosed and/or misdiagnosed in this sample. It remains to be seen,
however, whether the improved detection of SAD in primary care will in turn
result in improved patient outcome.
Treatment implications
Seasonal affective disorder is thought to be related to seasonal variations
in natural light levels, and light therapy daily exposure of the
patient to bouts of artificially produced high-intensity light has
been shown to produce amelioration of depressive symptoms
(Eastman et al, 1998;
Terman et al, 1998).
Early research has also indicated that antidepressants may be successful in
treating SAD (Lam et al,
1995). However, with lightboxes costing in the region of
£150 for an indefinite treatment period compared to £120 for a
winter's supply of fluoxetine, light therapy remains for some clinicians a
potentially less expensive and less invasive form of treatment. Furthermore,
given that current treatment guidelines suggest that antidepressants be
prescribed for non-seasonal depression for a minimum of 6 months, is it also
feasible that patients with unrecognised SAD are currently receiving
medication for longer than necessary. The cost implications of this potential
overprescribing are significant. In this regard, a more targeted approach
towards SAD by better-informed primary health care teams is likely to benefit
the NHS as well as the patient.
Methodological considerations
The prevalence rate obtained in the present study may have been inflated in
two ways. First, a higher response rate was received from women, and women are
more likely than men to suffer from SAD. Second, a stage one bias towards
response may have occurred in people who experience seasonal problems. Another
methodological consideration concerns the decision to offer diagnostic
interviews to only a 5% sample of participants. This may have led to
considerably higher standard errors (and hence wider confidence intervals)
than would have been the case if a larger proportion of participants had been
included in the second phase of the community survey.
Furthermore, response rates were particularly poor for this group, resulting in only a 1.2% (n=23) random sample actually being interviewed. It later became evident that the research team had placed less emphasis upon achieving a high response rate in this group than in the screen-positive sample.
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Clinical Implications and Limitations |
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LIMITATIONS
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ACKNOWLEDGMENTS |
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REFERENCES |
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Received for publication August 3, 2000. Revision received January 18, 2001. Accepted for publication January 24, 2001.
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