Diagnosis and prognosis of major depressive disorder: from clinical to biological applications

Current diagnosis of Major Depressive Disorder is primarily based on clinical
assessment by a certified psychiatrist or clinical psychologist. It is clear however that this procedure has several limitations. Firstly, MDD is a syndrome with a complex and varying symptom profile including several subtypes, pointing at a heterogeneous clinical and pathophysiological background. Secondly, many clinical symptoms of MDD have also been associated with other psychiatric disorders. This heterogeneity not only complicates diagnosis of MDD but also the prognosis of treatment outcome. Recent advances in deciphering the biological substrate of MDD and other psychiatric disorders may clear the path for a more biologically oriented approach. Within this chapter we will review the limitations of current diagnostical tools for MDD and how recent advances in understanding the biological background of MDD could improve current diagnosis and treatment of MDD. We will also discuss problems inherent to the biological approach and how we might overcome these difficulties.