The investigation into depressive symptoms begins with inquiries of the neurovegetative symptoms which include changes in sleeping patterns, appetite, and energy levels. Positive responses should elicit further questioning focused on evaluating for the presence of the symptoms which are diagnostic of major depression. These are the 9 symptoms listed in the DSM-5. Five must be present to make the diagnosis (one of the symptoms should be depressed mood or loss of interest or pleasure):

1. Sleep disturbance
2. Interest/pleasure reduction
3. Guilt feelings or thoughts of worthlessness
4. Energy changes/fatigue
5. Concentration/attention impairment
6. Appetite/weight changes
7. Psychomotor disturbances
8. Suicidal thoughts
9. Depressed mood

All patients with depression should be evaluated for suicidal risk. Any suicide risk must be given prompt attention which could include hospitalization or close and frequent monitoring.

Other areas of investigation include:

1. Past medical history and family medical history, and current medications
2. Social history with a focus on stressors and the use of drugs and alcohol
3. History and physical examination to rule out organic causes of depression. Depressive symptoms and their severity are also evaluated with the help of questionnaires such as the Beck's Depression Inventory (BDI), Hamilton Depression Scale (Ham-D), and Zung Self Rating Depression Scale

The diagnosis of depression is based on history and physical findings. No diagnostic laboratory tests are available to diagnose major depressive disorder. Laboratory studies are, however, useful to exclude medical illnesses that may present as major depressive disorder. [6][7][8]These laboratory studies might include the following:

• Complete blood cell (CBC) count
• Thyroid-stimulating hormone (TSH)
• Vitamin B-12
• Rapid plasma reagin (RPR)
• HIV test
• Electrolytes, including calcium, phosphate, and magnesium levels
• Blood urea nitrogen (BUN) and creatinine
• Liver function tests (LFTs)
• Blood alcohol level
• Blood and urine toxicology screen
• Arterial blood gas (ABG)
• Dexamethasone suppression test (Cushing disease, but also positive in depression)
• Cosyntropin (ACTH) stimulation test (Addison disease)  
• Computed tomography (CT) scanning or magnetic resonance imaging (MRI) of the brain should be considered if organic brain syndrome or hypopituitarism is included in the differential diagnosis

Medication alone and brief psychotherapy (cognitive-behavioral therapy, interpersonal therapy) alone can relieve depressive symptoms. Combination therapy has also been associated with significantly higher rates of improvement in depressive symptoms; increased quality of life; and better treatment compliance. There is also empirical support for the ability of CBT to prevent relapse.[9][10]

Electroconvulsive therapy is useful for patients who are not responding well to medications or are suicidal.[11][1]

Medications

1. Selective serotonin reuptake inhibitors (SSRIs)
2. Serotonin/norepinephrine reuptake inhibitors (SNRIs)     
3. Atypical antidepressants
4. Serotonin-Dopamine Activity Modulators (SDAMs)     
5. Tricyclic antidepressants (TCAs)
6. Monoamine oxidase inhibitors (MAOIs)  
7. Selective serotonin reuptake inhibitors (SSRIs): SSRIs have the advantage of ease of dosing and low toxicity in overdose. They are also the first-line medications for late-onset depression.
8. SSRIs include: Citalopram, escitalopram, fluoxetine,  fluvoxamine, paroxetine, sertraline, vilazodone, vortioxetine
9. Serotonin/norepinephrine reuptake inhibitors (SNRIs): SNRIs, which include venlafaxine, desvenlafaxine, duloxetine, and levomilnacipran can be used as first-line agents, particularly in patients with significant fatigue or pain syndromes associated with the episode of depression. SNRIs also have an important role as second-line agents in patients who have not responded to SSRIs. 
10. Atypical antidepressants: Atypical antidepressants include bupropion, mirtazapine, nefazodone, and trazodone. They have all been found to be effective in monotherapy in major depressive disorder and may be used in combination therapy for more difficult to treat depression.
11. Serotonin-Dopamine Activity Modulators (SDAMs): SDAMs include brexpiprazole and aripiprazole. SDAMs act as a partial agonist at 5-HT1A and dopamine D2 receptors at similar potency, and as an antagonist at 5-HT2A and noradrenaline alp Brexpiprazole is indicated as adjunctive therapy for major depressive disorder (MDD).
12. Tricyclic antidepressants (TCAS): TCAs include the following: Amitriptyline, clomipramine, desipramine, doxepin, imipramine, nortriptyline, protriptyline, trimipramine. TCAs have a long record of efficacy in the treatment of depression. They are used less commonly because of their side-effect profile and their considerable toxicity in overdose.
13. Monoamine oxidase inhibitors (MAOIs): MAOIs include isocarboxazid, phenelzine, selegiline, and tranylcypromine. These agents are widely effective in a broad range of affective and anxiety disorders. Because of the risk of hypertensive crisis, patients on these medications must follow a low-tyramine diet. Other adverse effects can include insomnia, anxiety, orthostasis, weight gain, and sexual dysfunction.

Electroconvulsive Therapy (ECT)

ECT is a highly effective treatment for depression. Onset of action may be more rapid than that of drug treatments, with benefit often seen within 1 week of commencing treatment. A course of ECT (usually up to 12 sessions) is the treatment of choice for patients who do not respond to drug therapy, are psychotic, or are suicidal or dangerous to themselves. Thus, the indications for the use of ECT include the following:

1. Need for a rapid antidepressant response  Failure of drug therapies   
2. History of a good response to ECT     
3. Patient preference     
4. High risk of suicide
5. High risk of medical morbidity and mortality

Although advances in brief anesthesia and neuromuscular paralysis have improved the safety and tolerability of ECT, this modality poses numerous risks, including those associated with general anesthesia, postictal confusion, and, more rarely, short-term memory difficulties.  

Psychotherapy

Cognitive Behavior Therapy and Interpersonal Therapy are evidence-based psychotherapies that have been found to be effective in the treatment of depression.

Cognitive-behavioral therapy (CBT)

CBT is a structured, and didactic form of therapy that focuses on helping individuals identify and modify maladaptive thinking and behavior patterns (16 to 20 sessions). It is based on the premise that patients who are depressed exhibit the “cognitive triad” of depression, which includes a negative view of themselves, the world, and the future. Patients with depression also exhibit cognitive distortions that help to maintain their negative beliefs. CBT for depression typically includes behavioral strategies (i.e., activity scheduling), as well as cognitive restructuring to change negative automatic thoughts and addressing maladaptive schemas.

There is evidence supporting the use of CBT with individuals of all ages. It is also considered being efficacious for the prevention of relapse. It is particularly valuable for elderly patients, who may be more prone to problems or side effects with medications.  

Mindfulness-based cognitive therapy (MBCT) was designed to reduce relapse among individuals who have been successfully treated for an episode of recurrent major depressive disorder. The primary treatment component is mindfulness training. MBCT specifically focuses on ruminative thought processes as being a risk factor for relapse. Research indicates that MBCT is effective in reducing the risk of relapse in patients with recurrent depression, especially in those with the most severe residual symptoms. Interpersonal therapy (IPT)

Interpersonal Therapy (IPT)

Interpersonal therapy (IPT) is a time-limited (typically 16 sessions) treatment for major depressive disorder. IPT draws from attachment theory and emphasize the role of interpersonal relationships, focusing on current interpersonal difficulties. Specific areas of emphasis include grief, interpersonal disputes, role transitions, and interpersonal deficits.

• Adjustment disorders

• Anaemia

• Chronic Fatigue syndrome

• Dissociative disorders

• Illness anxiety disorders

• Hypoglycemia

• Hypopituitarism

• Schizoaffective disorders

• Schizophrenia

• Somatic symptom disorders

Major depression has very high morbidity and mortality contributing to high rates of suicide. Even though effective drug treatment is available, nearly 50% may not initially respond. Complete remission is not common but at least 40% achieve partial remission in 12 months.

However, relapses are common and many patients require a variety of treatments to control the symptoms. The quality of life of most patients with depression is poor.

Depression accounts for nearly 40,000 cases of suicide each year in the US. The highest rate of suicides is in older men.

Depression is a very common disorder encountered by the nurse practitioner, primary care provider, psychiatrist, and mental health worker, coordinating as an interprofessional healthcare team. The disorder has extremely high morbidity including the risk of suicide. All healthcare workers should be knowledgeable about this disorder and refer the patient to a psychiatrist if there is a risk of self-harm.

Education plays an important role in the successful treatment of major depressive disorder. This would include the education of the family and the patient. Lack of accurate information and misperceptions of the illness as a personal weakness or failings leads to painful stigmatization and avoidance of the diagnosis by many of those affected. Patients should know the rationale behind the choice of treatment, potential adverse effects, and expected results.

The involvement of the pharmacist in the treatment plan can enhance medication compliance and referral for psychotherapy. The pharmacist can also check that dosing is appropriate, that there are no significant interactions, and counsel on adverse effects. Engaging family members can be a critical component of a treatment plan. Family members are helpful informants, can ensure medication compliance, be a big source of social support and can encourage patients to change behaviors that perpetuate depression (e.g., inactivity).

Patients with moderate to severe depression should also be seen by a social worker or case management nurse to ensure that they have a support system and finances for treatment. If there is a concern, the person managing the case should present the issues to the interprofessional team so that a plan can be developed to get the patient the care they need.  Overall, depression is managed by an interprofessional team dedicated to the management of mental health disorders. Open communication between all the members of the interprofessional team is the key to lowering the morbidity of the disorder. [Leve 5]

Outcomes

The outcomes for patients with depression are guarded. There is no cure and the condition has frequent relapses and remissions, leading to a poor quality of life.[3][12][13]