Revisiting depression: Nosological challenges in the third millennium

Depression is one of the most prevalent psychiatric disorders. The concept, etiology, phenomenology, biological and cultural perspectives, and psychosocial management of depression have come a long way and evolved over around 75 years.[1,2] In the 1960s, depression was divided into endogenous and exogenous depression. This theory of depression distinguished depression not only symptomatically but also etiologically. Overruling these concepts, in the 1980s–1990s, DSM-III, DSM-IV, and ICD-10 relied on stringent symptomatic criteria. In these classifications, depression was considered a clinical syndrome, but etiological, psychological, and biological factors, which may have a direct and indirect causative role in depression, were not considered. Further, these stringent bars led to underdiagnosing the disorder in many patients who could not fit the criteria.[3] Finally, in the third millennium, DSM-5 and ICD-11 focused on treatment as per the symptoms and neurobiological findings.[4] While moving from the categorical to dimensional approach of the ICD-11 classificatory system, depression is described in detail, considering the symptom qualifiers. This system underlies the concept of various theories, namely, the monoamine hypothesis, neurotrophic/neuroplasticity hypothesis, neuroendocrine hypothesis, permissive hypothesis, electrolyte membrane hypothesis, and more recently, immune-inflammatory theory, mitochondrial dysfunction theory, gut dysbiosis theory, social control theory, and cognitive theory.[5,6] The Research Domain Criteria (RDoC) initiative was being considered a comprehensive, alternative classification framework for understanding the neuropsychiatric ailments. Different aspects of each domain or constructs help understand the dysfunction in fundamental psychological/biological systems.[7] Biopsychosocial enlightening has paved the way for delving into psychopathology, the mechanism, and the newer perspectives for treating depression. The role of psychosocial interventions has been enhanced in the last 50 years in managing depression.[2,6] Also, the current world's psychosocial issues, eating habits, and lifestyle have significantly affected the gut microbiome and, ultimately, the gut-brain axis. This thus triggers depressive symptoms by initiating central inflammation, oxidative stress, and neuronal death.[4-6] The effort of the current classificatory system was to make a more homogeneous group of symptoms for a particular mental disorder. However, because of a significant degree of psychosocial and genetic variations, it is challenging to conceptualize it in this manner. Future researchers should look at how individuals with similar psychosocial issues can be categorized in the same diagnostic category. The social psychopathology of depression has been intensified in the 21st century due to significant numbers of childhood adversities, social maladjustments, disastrous wars, refugees, asylum seekers, and homeless individuals. In conclusion, the psychopathology of depression usually differs in different individuals. In the journey of various concepts of depression, the intersection of psychosocial and genetic makeup holds immense promise for understanding depression. Depression still faces challenges in terms of clear diagnostic criteria. As we travel into the 21st century, further exploration of novel methods and precise diagnostic tools for the benefit of patients is needed to refine our understanding of depression. Financial support and sponsorship Nil. Conflicts of interest There are no conflicts of interest.