A brief overview of the changes from DSM IV to DSM-5 about "mood disorders" could be: "1. Change of diagnostic category", "2. Addition of new specifiers", and "3. Suggestion of severity assessment tools". The main impact of 1. Change of diagnostic category could be that the "mood disorder" category has disappeared and it has been divided into bipolar disorder and major depressive disorder (MDD), This change was based on the evidence that MDD is distinct from bipolar disorder in the light of genetic and brain structures compared to schizophrenia. Some risk-associated genes have been detected related to bipolar disorder and schizophrenia but not to MDD. This could be due to low inter-rater reliability regarding MDD. Furthermore, the specificity of MDD diagnostic criteria is low and various other depression-like disorders that are pathophysiologically different from MDD could be included in the criteria as a phenocopy. Diagnosis from a dimensional point of view with new specifiers and severity assessment tools, described above as points "2" and "3", added to DSM-5 could characterize MDD in more detail and solve this problem related to low inter-rater reliability. A dimensional approach could not only identify specific phenotypes in further research but also clinically provide valuable information to put evidence to practical use. In this review, I would like to focus on the significance of the changes in DSM-5 and provide some suggestions on how we should use DSM-5 in clinical and research settings.
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