Abstract
Major depressive disorder (MDD), also known as clinical depression or unipolar depression, is a common but serious mood disorder that negatively affects how an individual feels, thinks and behaves. According to the Diagnostic and Statistical Manual of Mental Disorders (5th ed.; DSM–5; American Psychiatric Association [APA], 2013), a person diagnosed with MDD must present with a depressed mood or loss of interest or pleasure in life activities for a minimum of two weeks along with at least four additional symptoms that reflect changes in cognitive, emotional, motivational, physical and psychological functioning. Left untreated, depression can reduce an individual’s ability to function at work or school, maintain basic self-care, and destroy important relationships. Fortunately, depression is highly treatable with psychotherapy, medication or both. This paper provides an overview of MDD including its diagnostic criteria and major causes and risk factors. Treatment options and prevention strategies to reduce the impact of depression on individuals and society are also discussed.
Major Depressive Disorder: Diagnostic Criteria and Prevalence
According to the DSM-5, a diagnosis of MDD requires at least five or more of the following symptoms be present during the same two-week period and represent a change from previous functioning: 1) Depressed mood most of the day, nearly every day, as indicated by either subjective report (e.g., feels sad, empty, hopeless) or observation made by others (e.g., appears tearful); 2) Markedly diminished interest or pleasure in all, or almost all, activities most of the day, nearly every day; 3) Significant weight loss when not dieting or weight gain (e.g., a change of more than 5% of body weight in a month), or decrease or increase in appetite nearly every day; 4) Insomnia or hypersomnia nearly every day; 5) Psychomotor agitation or retardation nearly every day (observable by others, not merely subjective feelings of restlessness or being slowed down); 6) Fatigue or loss of energy nearly every day; 7) Feelings of worthlessness or excessive or inappropriate guilt nearly every day (which may be delusional); 8) Diminished ability to think or concentrate, or indecisiveness, nearly every day (either by subjective account or as observed by others); and 9) Recurrent thoughts of death (not just fear of dying), recurrent suicidal ideation without a specific plan, or a suicide attempt or a specific plan for committing suicide (APA, 2013, pp. 160-161).
In addition to the aforementioned symptom criteria, the DSM-5 specifies that the symptoms cause clinically significant distress or impairment in social, occupational, or other important areas of functioning. Episodes of MDD can be characterized as mild (few, if any symptoms in excess of minimum criteria), moderate (symptoms or functional impairment between mild and severe), or severe (most symptoms and the symptoms resulting in severe impairment) (APA, 2013, p. 165). The lifetime prevalence of MDD in the United States is estimated to be 16.2% and the past-year prevalence is around 6.7% (National Institute of Mental Health, n.d.). Depression is one of the most common mental disorders and a major contributor to the global burden of disease (World Health Organization, 2017).
Major Causes and Risk Factors of Depression
While the exact causes of depression are unknown, it likely results from a complex interaction of genetic, biological, environmental, and psychological factors. From a biological perspective, abnormalities in certain brain structures and circuits involved in regulating mood and emotions have been implicated in depression. Brain imaging studies have found changes in the prefrontal cortex and limbic regions like the amygdala, hippocampus, and striatum in people with MDD (Delvecchio, Berlin, & Kaczmarek, 2019). Additionally, imbalances in neurotransmitter systems including serotonin, norepinephrine and dopamine have been linked to depression. Environmental and psychological stressors such as difficult life events, trauma, lack of social support networks, and childhood adversity increase the risk of developing depression by disrupting neurobiological processes underlying normal mood regulation (Tesarz & Erdmann, 2016).
Genetic contributions are estimated to account for 31-42% of vulnerability to depression with heritability potentially higher for earlier age of onset, recurrent episodes, psychotic features, and bipolar disorder (Levinson & Druss, 2016). People with a first-degree relative, especially a parent, who has experienced depression are 2-3 times more likely to develop MDD themselves (Trivedi et al., 2015). Certain personality traits including neuroticism and low self-esteem also make depression more likely (Weinstock & Whisman, 2017). Having chronic physical health conditions such as cancer, heart disease, diabetes, chronic pain, obesity, stroke, and Parkinson’s disease increases risk as well through shared neurobiological mechanisms and psychosocial pathways (Amaral et al., 2015). Psychologically, early childhood trauma including abuse, neglect, and unstable family environments have a robust prospective association with adult depression (Risch, Herzog, & Nigg, 2017).
Depression Treatments and Prevention Strategies
Given its high prevalence and significant economic costs, effective treatments for MDD are vital. The predominant treatment modalities are pharmacotherapy, psychotherapy and brain stimulation therapies. Selective serotonin reuptake inhibitors (SSRIs) are typically the first-line antidepressant medication due to their favorable risk-benefit ratio (Baldwin et al., 2018). Other antidepressants prescribed include serotonin and norepinephrine reuptake inhibitors (SNRIs), norepinephrine and dopamine reuptake inhibitors (NDRIs), and tricyclic antidepressants, among others (Charney et al., 2018). When medication alone proves ineffective, combining it with psychotherapy is often more beneficial than either alone (Brams et al., 2016).
The most researched psychotherapies for depression include cognitive behavioral therapy (CBT), interpersonal therapy (IPT), behavioral therapies, and psychodynamic psychotherapy (Lubman & Gil, 2018). CBT teaches skills for identifying and modifying negative thought patterns and behaviors that perpetuate depression. IPT addresses current interpersonal problems that may underlie or exacerbate depression. Behavioral activation aims to reverse inactivity and withdrawal by scheduling enjoyable activities and reducing avoidance. Supportive strategies can prevent relapse such as maintaining adequate treatment duration and providing follow-up care after achieving remission of symptoms (Holter et al., 2016).
Newer treatments under investigation are deep brain stimulation (DBS), ketamine, and magnetic seizure therapy (MST), which involve directly stimulating areas of the brain linked to mood regulation (Eipe et al., 2016). Effective prevention strategies include reducing childhood adversity, enhancing social support, promoting healthy lifestyle behaviors, treating anxiety disorders early, monitoring mood in high-risk groups, and screening for and treating depression during and after pregnancy (Botega, Barros, & Dalgalarrondo, 2017). Raising awareness through public education campaigns serves to reduce stigma and improve access to depression care through early help-seeking and identification of depression by family and friends.
Discussion
MDD is a highly prevalent mental disorder characterized by a persistently low mood and related cognitive, physical and behavioral symptoms. Left untreated, depression can severely impair quality of life and functional capacity. Depression is also highly treatable with various psychopharmacological and psychotherapeutic interventions. While the precise causes are multifactorial, genetic, neurobiological, psychological, environmental and medical factors have been identified as contributing to depression risk. Key prevention strategies aim to reduce childhood adversity, enhance social support systems, promote healthy lifestyle management, and screen for early identification of depression in high-risk populations. Future research continues to provide insights into the pathophysiology of depression to develop more effective and individualized treatment approaches. Overall, improved awareness, timely diagnosis and treatment of depression have the potential to significantly reduce the individual and societal burden of this common yet potentially disabling mental health condition.
Andrew Stroud