All patients must meet the diagnostic criteria for recurrent major depression or bipolar mood disorder. Seasonal affective disorder (SAD) is then a sub-type specifier used to describe temporal variations of these disorders. As such, SAD is not considered a stand-alone diagnosis or comorbid condition to recurrent major depression or bipolar disorder. Common presentations include the initiation or worsening of depressive symptoms during the autumn or winter months, and full remission during the spring or summer months, or hypo-manic or manic symptoms presenting during spring or summer months.
Circadian and neurotransmitter factors are likely to contribute to the pathophysiology of SAD, although the exact mechanism of action remains ill-understood. The suprachiasmatic nucleus (SCN) of the hypothalamus is being increasingly recognised as the 'master regulator' of several systems implicated in seasonal mood regulation. Diminished light during the autumn and winter may cause a phase shift in various circadian rhythms, including sleep-wake cycle, body temperature, hormone levels, and melatonin secretion.
The reported frequency of adjustment disorder varies widely, depending on the population studied and the assessment methods used. A number of studies have reported rates around 12% across a variety of populations. In clinical patient populations, rates as high as 23% have been recorded.Depressed mood was the most common subtype assigned (11.6%), followed by anxious mood, mixed anxiety and depressed mood, and disturbance of conduct.In a survey of mental health−related hospitalizations in the US Armed Forces between 2000 and 2012, 49,790 of 192,317 hospitalizations of active duty personnel (38%) were related to adjustment disorder.According to DSM-5, a principal diagnosis of adjustment disorder is made in approximately 5-20% of individuals undergoing outpatient mental health treatment. In the setting of a hospital psychiatric consultation service, adjustment disorder is often the most common diagnosis, with frequencies as high as 50%.