Seasonal patterns of illness have been recognized since ancient times, but the concept of seasonality in psychiatric disorders has only gained prominence in the past two decades. This article will briefly review the diagnosis, treatment and pathophysiology of winter seasonal affective disorder (SAD).Diagnostic and Clinical Features
The DSM-IV-TR diagnostic criteria classify SAD as a subtype or "course specifier" for recurrent major depressive episodes within major depressive disorder or bipolar disorder (BD). However, only a minority of patients are diagnosed as having BD (Lam, 1998b).
The stability of the SAD diagnosis is similar to other depressive subtypes. Longitudinal studies of one to 10 years of follow-up showed that about 30% of patients continued to have seasonal episodes, about 20% were in remission (some because of treatment) and the remaining 50% had complex patterns that were not strictly seasonal (Schwartz et al., 1996; Thompson et al., 1995). Like other forms of depression, SAD is associated with significant morbidity and health service utilization (Eagles et al., 2002).
Although not included in the diagnostic criteria, SAD is also associated with so-called atypical vegetative symptoms, including carbohydrate craving, increased appetite, weight gain and hypersomnia/morning fatigue (Lam, 1998b; Oren and Rosenthal, 1992; Winkler et al., 2002) (Table). While these symptoms are also found in atypical depression, the rejection sensitivity commonly seen in atypical depression is not prominent in SAD (Tam et al., 1997). Atypical symptoms appear to be predictive of good response to light therapy (Terman et al., 1996).
Studies using the Seasonal Pattern Assessment Questionnaire (SPAQ) estimated the prevalence of winter SAD in North America to be approximately twice that of Europe (Mersch et al., 1999). The differences between North American and European studies may be related to translation issues with the SPAQ, cultural response biases, genetic differences in seasonality, climatic variation or other factors. Regardless, studies using the SPAQ are likely to overestimate the prevalence of SAD because clinical diagnoses are not obtained.
Community studies using diagnostic interviews estimated the prevalence of SAD by DSM-III-R or DSM-IV criteria as 2.6% in Ontario, Canada (Levitt and Boyle, 2002), and 0.4% in the United States (Blazer et al., 1998). Seasonal affective disorder is more prevalent with higher (more northern) latitudes, but the correlation between latitude and prevalence is modest (Levitt and Boyle, 2002; Mersch et al., 1999).Treatment Options
Light therapy. An early meta-analysis of over two dozen studies using fluorescent light boxes found that bright light treatment was superior to control conditions (Terman et al., 1989). However, these findings were criticized for methodological limitations, including small sample sizes and use of dim light as placebo controls.