Major depressive disorder (MDD) has been ranked as the third cause of the burden of disease worldwide in 2008 by WHO, which has projected that this disease will rank first by 2030. It is diagnosed when an individual has a persistently low or depressed mood, anhedonia or decreased interest in pleasurable activities, feelings of guilt or worthlessness, lack of energy, poor concentration, appetite changes, psychomotor retardation or agitation, sleep disturbances, or suicidal thoughts. Per the Diagnostic and Statistical Manual of Mental Disorders, 5th Edition (DSM-5), an individual must have five of the above-mentioned symptoms, of which one must be a depressed mood or anhedonia causing social or occupational impairment, to be diagnosed with MDD. History of a manic or hypomanic episode must be ruled out to make a diagnosis of MDD. Children and adolescents with MDD may present with irritable mood.
Per DSM-5, other types of depression falling under the category of depressive disorders are:
The etiology of Major depressive disorder is believed to be multifactorial, including biological, genetic, environmental, and psychosocial factors. MDD was earlier considered to be mainly due to abnormalities in neurotransmitters, especially serotonin, norepinephrine, and dopamine. This has been evidenced by the use of different antidepressants such as selective serotonin receptor inhibitors, serotonin-norepinephrine receptor inhibitors, dopamine-norepinephrine receptor inhibitors in the treatment of depression. People with suicidal ideations have been found to have low levels of serotonin metabolites. However, recent theories indicate that it is associated primarily with more complex neuroregulatory systems and neural circuits, causing secondary disturbances of neurotransmitter systems.
GABA, an inhibitory neurotransmitter, and glutamate and glycine, both of which are major excitatory neurotransmitters are found to play a role in the etiology of depression as well. Depressed patients have been found to have lower plasma, CSF, and brain GABA levels. GABA is considered to exert its antidepressant effect by inhibiting the ascending monoamine pathways, including mesocortical and mesolimbic systems. Drugs that antagonize NMDA receptors have been researched to have antidepressant properties. Thyroid and growth hormonal abnormalities have also been implicated in the etiology of mood disorders. Multiple adverse childhood experiences and trauma are associated with the development of depression later in life.
Severe early stress can result in drastic alterations in neuroendocrine and behavioral responses, which can cause structural changes in the cerebral cortex, leading to severe depression later in life. Structural and functional brain imaging of depressed individuals has shown increased hyperintensities in the subcortical regions, and reduced anterior brain metabolism on the left side, respectively. Family, adoption, and twin studies have indicated the role of genes in the susceptibility of depression. Genetic studies show a very high concordance rate for twins to have MDD, particularly monozygotic twins. Life events and personality traits have shown to play an important role, as well. The learned helplessness theory has associated the occurrence of depression with the experience of uncontrollable events. Per cognitive theory, depression occurs as a result of cognitive distortions in persons who are susceptible to depression.
Major depressive disorder is a highly prevalent psychiatric disorder. It has a lifetime prevalence of about 5 to 17 percent, with the average being 12 percent. The prevalence rate is almost double in women than in men. This difference has been considered to be due to the hormonal differences, childbirth effects, different psychosocial stressors in men and women, and behavioral model of learned helplessness. Though the mean age of onset is about 40 years, recent surveys show trends of increasing incidence in younger population due to the use of alcohol and other drugs of abuse.
MDD is more common in people without close interpersonal relationships, and who are divorced or separated, or widowed. No difference in the prevalence of MDD has been found among races and socioeconomic status. Individuals with MDD often have comorbid disorders such as substance use disorders, panic disorder, social anxiety disorder, and obsessive-compulsive disorder. The presence of these comorbid disorders in those diagnosed with MDD increases their risk of suicide. In older adults, depression is prevalent among those with comorbid medical illnesses. Depression is found to be more prevalent in rural areas than in urban areas.
Major depressive disorder is a clinical diagnosis; it is mainly diagnosed by the clinical history given by the patient and mental status examination. The clinical interview must include medical history, family history, social history, and substance use history along with the symptomatology. Collateral information from a patient's family/friends is a very important part of psychiatric evaluation.
A complete physical examination, including neurological examination, should be performed. It is important to rule out any underlying medical/organic causes of a depressive disorder. A full medical history, along with the family medical and psychiatric history, should be assessed. Mental status examination plays an important role in the diagnosis and evaluation of MDD.
Although there is no objective testing available to diagnose depression, routine laboratory work including complete blood account with differential, comprehensive metabolic panel, thyroid-stimulating hormone, free T4, vitamin D, urinalysis, and toxicology screening is done to rule out organic or medical causes of depression.
Individuals with depression often present to their primary care physicians for somatic complaints stemming from depression, rather than seeing a mental health professional. In almost half of the cases, patients deny having depressive feelings, and they are often brought for treatment by the family or sent by the employer to be evaluated for social withdrawal and decreased activity. It is very important to evaluate a patient for suicidal or homicidal ideations at each visit.
In primary care settings, the Patient Health Questionnaire-9 (PHQ-9), which is a self-report, standardized depression rating scale is commonly used for screening, diagnosing, and monitoring treatment response for MDD. The PHQ-9 uses 9 items corresponding to the DSM-5 criteria for MDD and also assesses for psychosocial impairment. The PHQ-9 scores 0 to 27, with scores of equal to or more than 10, indicate a possible MDD.
In most hospital settings, the Hamilton Rating Scale for Depression (HAM-D), which is a clinician-administered depression rating scale is commonly used for the assessment of depression. The original HAM-D uses 21 items about symptoms of depression, but the scoring is based only on the first 17 items.
Other scales include the Montgomery-Asberg Depression Rating Scale (MADRS), the Beck Depression Inventory (BDI), the Zung Self-Rating Depression Scale, the Raskin Depression Rating Scale, and other questionnaires.
Major depressive disorder can be managed with various treatment modalities, including pharmacological, psychotherapeutic, interventional, and lifestyle modification. The initial treatment of MDD includes medications or/and psychotherapy. Combination treatment, including both medications and psychotherapy, has been found to be more effective than either of these treatments alone. Electroconvulsive therapy is found to be more efficacious than any other form of treatment for severe major depression.
FDA-approved medications for the treatment of MDD are as follows: All antidepressants are equally effective but differ in side-effect profiles.
Electroconvulsive therapy (ECT)
Transcranial magnetic stimulation (TMS)
Vagus nerve stimulation (VNS)
While evaluating for MDD, it is important to rule out depressive disorder due to another medical condition, substance/medication-induced depressive disorder, dysthymia, cyclothymia, bereavement, adjustment disorder with depressed mood, bipolar disorder, schizoaffective disorder, schizophrenia, anxiety disorders, and eating disorders for the appropriate management. Depressive symptoms can be secondary to the following causes:
Untreated depressive episodes in major depressive disorder can last from 6 to 12 months. About two-thirds of the individuals with MDD contemplate suicide, and about 10 to 15 percent commit suicide. MDD is a chronic, recurrent illness; the recurrence rate is about 50% after the first episode, 70% after the second episode, and 90% after the third episode. About 5 to 10 percent of the patients with MDD eventually develop bipolar disorder. The prognosis of MDD is good in patients with mild episodes, the absence of psychotic symptoms, better treatment compliance, a strong support system, and good premorbid functioning. The prognosis is poor in the presence of a comorbid psychiatric disorder, personality disorder, multiple hospitalizations, and advanced age of onset.
MDD is one of the leading causes of disability worldwide. It not only causes a severe functional impairment but also adversely affects the interpersonal relationships, thus lowering the quality of life. Individuals with MDD are at a high risk of developing comorbid anxiety disorders and substance use disorders, which further increases their risk of suicide. Depression can aggravate medical comorbidities such as diabetes, hypertension, chronic obstructive pulmonary disease, and coronary artery disease. Depressed individuals are at high risk of developing self-destructive behavior as a coping mechanism. MDD is often very debilitating if left untreated.
Patient education has a profound impact on the overall outcome of major depressive disorder. Since MDD is one of the most common psychiatric disorders causing disability worldwide and people in different parts of the world are hesitant to discuss and seek treatment for depression due to the stigma associated with mental illness, educating patients is very crucial for their better understanding of the mental illness and better compliance with the mental health treatment. Family education also plays an important role in the successful treatment of MDD.
An interdisciplinary approach is essential for the effective and successful treatment of MDD. Primary care physicians and psychiatrists, along with nurses, therapists, social workers, and case managers, form an integral part of these collaborated services. In the majority of cases, PCPs are the first providers to whom individuals with MDD present mostly with somatic complaints. Depression screening in primary care settings is very imperative. The regular screening of the patients using depression rating scales such as PHQ-9 can be very helpful in the early diagnosis and intervention, thus improving the overall outcome of MDD. Psychoeducation plays a significant role in improving patient compliance and medication adherence. Recent evidence also supports that lifestyle modification, including moderate exercises, can help to improve mild-to-moderate depression. Suicide screening at each psychiatric visit can be helpful to lower suicide incidence. Since patients with MDD are at increased risk of suicide, close monitoring, and follow up by mental health workers becomes necessary to ensure safety and compliance with mental health treatment. The involvement of families can further add to a better outcome of the overall mental health treatment. Meta-analyses of randomized trials have shown that depression outcomes are superior when using collaborative care as compared with usual care.
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