Recent systematic review s have shown that  light therapy  is an efficacious and well-tolerated treatment for SAD .
There is also evidence for efficacy of pharmacotherapy to treat and prevent SAD .
SAD is a common condition with significant psychosocial impairment .
BACKGROUND Seasonal affective disorder ( SAD ) consists of recurrent major depressive episodes in the fall/winter with remissions in spring/summer .
RESULTS A careful history is important to make the diagnosis and differentiate SAD from other similar conditions such as subsyndromal SAD and atypical depression .
Seasonal patterns with winter worsening are also recognized in " nonseasonal " depression as well as many other psychiatric conditions , and comorbidity with SAD is common .
The pathophysiology of SAD seems to be heterogeneous as research on circadian , neurotransmitter function and genetic hypotheses have shown discrepant results .
A dual vulnerability model with differential loading on separate seasonal and depression factors has been proposed to explain these findings .
Seasonal depression: the dual vulnerability hypothesis revisited.
OBJECTIVE In DSM-IV , winter seasonal affective disorder ( SAD ) is classified as a seasonal pattern of recurrent major depressive episodes in winter with full remission of symptoms in summer . However , other groups with " winter depression " have been identified , including patients with incomplete summer remission ( ISR ) and subsyndromal SAD ( sub-SAD , winter depressive symptoms that do not meet criteria for major depression ) . In this study , we compare the clinical characteristics of these three seasonal groups and their response to light therapy . METHOD 558 patients assessed at a specialized SAD Clinic were diagnosed using DSM-III-R or DSM-IV criteria . Clinical information was recorded using a checklist at index assessment . A subset of patients ( N=192 ) were treated with an open , 2 week trial of light therapy using a 10000 lux fluorescent light box for 30 min per day in the early morning . Patients were assessed before and after treatment with the 29 item modified Hamilton Depression Rating Scale and clinical response was defined as greater than 50 % improvement in scores . RESULTS The rates of some melancholic symptoms , anxiety , panic , suicidal ideation , and family history of mood disorder were lowest in the sub-SAD group . The clinical response rates to light therapy  were highest in the sub-SAD group ( N=32 , 78 % ) , intermediate in the SAD group ( N=113 , 66 % ) , and lowest in the ISR group ( N=47 , 51 % ) . LIMITATIONS This was a retrospective study of patients seen in a specialty clinic , although information was obtained in a st and ardized format . The light therapy trial had an open design so that placebo response could not be determined . CONCLUSIONS There are differences in both the patterns of clinical symptoms and the response to light therapy  in these three groups with winter depression . These results are consistent with a dual vulnerability hypothesis that considers these groups to result from interaction of separate factors for seasonality and depression
Recent systematic review s have shown that  light therapy  is an efficacious and well-tolerated treatment for SAD .
There is also evidence for efficacy of pharmacotherapy to treat and prevent SAD .
SAD is a common condition with significant psychosocial impairment .
BACKGROUND Seasonal affective disorder ( SAD ) consists of recurrent major depressive episodes in the fall/winter with remissions in spring/summer .
RESULTS A careful history is important to make the diagnosis and differentiate SAD from other similar conditions such as subsyndromal SAD and atypical depression .
Seasonal patterns with winter worsening are also recognized in " nonseasonal " depression as well as many other psychiatric conditions , and comorbidity with SAD is common .
The pathophysiology of SAD seems to be heterogeneous as research on circadian , neurotransmitter function and genetic hypotheses have shown discrepant results .
A dual vulnerability model with differential loading on separate seasonal and depression factors has been proposed to explain these findings .