A three-year follow-up of major depression, dysthymia, minor depression and subsyndromal depression: results from a population-based study.

This study examined the 3-year outcome of major depression (MD)/dysthymic disorder (DD), minor depression (MinD), and subsyndromal symptomatic depression (SSD) in a population-based sample. The aims were to study the fluctuating nature of the symptoms of depression and to analyze the risk of fulfilling the criteria for MD/DD at the follow-up. An extensive questionnaire was sent out to persons ages 20-64 years registered in Stockholm County. Depression was assessed with the Major Depression Inventory. After 3 years the procedure was repeated, and 8,622 persons participated in both waves. Diagnoses of MD/DD, MinD, or SSD were made. Highest 3-year stability in fulfilling the criteria for a specific depressive category was found in MD/DD, and of those affected, only 35.9% had one or fewer symptoms of depression at the 3-year follow-up. The frequency of those with one or fewer symptom of depression was equal in MinD (58.9%) and in SSD (56.5%). The relative risk (RR) of fulfilling the criteria for MD/DD at Wave 2 was highest for those affected by MD/DD (RR=22.4) at Wave 1, whereas those fulfilling the criteria for MinD or SSD had similar rates (RR=4.8 and 5.0, respectively). This study supports the view that depression is a dimensional illness, with the affected persons moving in and out of diagnostic subtypes. The 3-year prognosis was severe in half of the affected persons in all three diagnostic depression categories.