[Severe depression : which concept ? which criteria].

Depression is a common disorder considered to be a serious public health problem although clinicians encounter very different levels of severity and the treatment strategies are tailored according to this variability. There are however no consensus criteria to define severe depression. This review presents and discusses the different possible qualitative and quantitative options. In the international classifications there are three levels of severity of episodes of major depression (mild, moderate, severe), which are defined above all on the number of diagnostic criteria found. There are other more qualitative severity factors : the presence of psychotic symptoms, melancholia and the presence of endogenous signs. Pronounced psychomotor retardation and risk of suicide are amongst the main clinical severity markers. Quantitative assessment scales for the severity of depression can also define severity thresholds for use for example in clinical studies. These thresholds are still poorly defined and vary between studies. Specific severity scales for melancholic depression or depression with psychomotor retardation can also be used in clinical studies for these factors, which are central to the concept of severe depression. Overall, the inclusion criteria for most studies combine severe depression with qualitative (clinicians' judgement) and quantitative (minimum score on a scale) aspects.