In medicine, the term depression denotes a true psychiatric disorder, often severely disabling, whose central clinical form is represented by the major depressive episode.
A major depressive episode is diagnosed when at least five of the nine symptom domains are present during the same period of at least two weeks, including at least one of depressed mood (or irritability in children and adolescents) and marked loss of interest or pleasure:
For the diagnosis to be valid, these symptoms must represent a clear change from premorbid functioning and cause clinically significant distress or significant impairment in social, occupational or personal functioning. In some cases, although the person appears functionally intact, this is maintained only through enormous internal effort. In severe cases, self-care may be completely abandoned (nutrition, hygiene, clothing).
The presentation must not be attributable to the physiological effects of a substance or another medical condition and must not be better explained by a psychotic disorder. A response to a significant loss, including bereavement, does not automatically exclude the diagnosis: duration, severity, impairment and clinical features must be assessed. The presence of manic or hypomanic symptoms instead requires reassessment within the bipolar disorders; mixed features may also be present.
In some individuals, depressive symptoms manifest predominantly as somatic complaints; irritability may predominate in children and adolescents. Diagnosis requires at least one of depressed mood and loss of interest or pleasure: anhedonia is therefore common but not necessarily present in every episode. Social withdrawal, abandonment of usual activities and reduced sexual desire may occur.
Appetite changes most often present as loss of appetite, although in some cases food intake may increase or specific food cravings may occur. In children, severe appetite impairment may prevent attainment of expected weight gain.
Insomnia is the most common sleep disturbance and may occur in several forms:
Less commonly, hypersomnia is observed, which may involve prolonged nighttime sleep or increased daytime hours spent sleeping. In many cases, sleep disturbance is the main reason for seeking medical advice.
Polysomnographic studies describe group-level alterations in sleep continuity, slow-wave sleep and REM architecture; the frequency and direction of findings vary, and polysomnography is not a routine diagnostic test for depression.
Psychomotor changes may manifest as agitation or motor slowing. To be clinically significant, they must also be observable by others and not be limited to subjective sensations. Reduced vital energy, asthenia, and easy fatigability are common even in the absence of physical activity.
Feelings of worthlessness and guilt may be excessive or inappropriate and may become delusional. The person may interpret neutral events as evidence of personal unworthiness or feel guilty about past mistakes, assuming disproportionate responsibility for adverse events.
Concentration is often impaired. The person reports difficulty thinking, making decisions, or remembering. In older adults, these symptoms may mimic the onset of dementia, complicating the differential diagnosis.
Thoughts of death are common and vary in severity. They may take the form of a belief that others would be better off without the person, recurrent suicidal ideation without a specific plan, or a concrete and detailed plan, sometimes accompanied by acquiring items intended for suicide (e.g., a rope or firearm). Risk increases with the specificity of the plan and availability of means, but it is impossible to predict with certainty whether or when the person will act.
Suicidal ideation may arise from a sense of helplessness in the face of difficulties perceived as insurmountable or from a wish to end an intolerable emotional state. In these cases, prompt clinical intervention is essential.
Individuals experiencing a major depressive episode frequently exhibit easy tearfulness, irritability, rumination, anxiety, obsessive concerns about health and difficulties in emotional and social relationships. School or work problems, psychoactive substance misuse and increased use of medical care are also common.
Symptoms may develop over days or weeks and may be preceded by prodromal symptoms. The duration of an untreated episode and the probability of remission vary widely among individuals and studies; residual symptoms or a chronic course may persist, with no single percentage applicable to all patients.
The pathophysiology of a major depressive episode is multifactorial. Neurobiological studies describe, in subgroups of patients, associations with monoaminergic and glutamatergic systems, the hypothalamic-pituitary-adrenal axis, immune-inflammatory processes, neuroplasticity and corticolimbic circuits; no single alteration constitutes a necessary or sufficient explanation of the disorder.
In some patients, alterations in cerebral metabolism and blood flow have been observed, with increased activity in limbic and paralimbic regions and reduced activity in lateral prefrontal areas. In older adults, depression may be associated with periventricular vascular lesions and other structural brain changes, suggesting an overlap with cerebrovascular disease.
A major depressive episode may present in a variety of clinical forms that influence severity, duration and therapeutic approach. When the episode is the most recent manifestation within a mood disorder, it may be further characterized with clinical specifiers.
Three severity levels are identified according to the number and intensity of symptoms and impairment:
According to its course, the episode may be further specified as:
In addition to severity and course, the episode may be characterized by additional clinical features:
Accurate definition of the specifiers is essential for appropriate treatment planning and prognosis. Episodes with melancholic or catatonic features, psychotic symptoms, or postpartum onset require careful specialist assessment and often more intensive, multimodal treatment.
The pathophysiology of a major depressive episode is heterogeneous and is not explained by a single neurochemical deficit. Group studies have found variable associations with monoaminergic and glutamatergic systems, the hypothalamic-pituitary-adrenal axis, immune processes, neuroplasticity, sleep and corticolimbic circuits; no finding is necessary, sufficient or usable as an individual diagnostic biomarker.
Neuroimaging and endocrine studies show average differences between groups, but their direction, frequency and clinical significance vary. Cerebrovascular lesions and other neurological factors may coexist in late-onset depression, without defining a single cause for all older patients.
A major depressive episode has an extremely variable course from one person to another. In most cases, symptoms develop over days or weeks, often preceded by a prodromal period characterized by sleep disturbances, anxiety, irritability, or reduced energy.
Duration and remission vary widely among individuals and studies. An episode may resolve, persist or leave residual symptoms; no single percentage applies to an individual patient without considering severity, comorbidity, treatment and the definitions used.
Recurrence is possible and risk increases with previous episodes, residual symptoms, early onset, severity and comorbidity. Estimates depend on population, follow-up duration and definitions and do not predict the individual course with certainty. Associated factors include:
Prognosis improves with early diagnosis and appropriate treatment, including pharmacotherapy, psychotherapy, and, in selected cases, integrated strategies or physical therapies (vagus nerve stimulation, TMS, and ECT).
Although not readily predictable, suicide risk is significantly increased in people with depression, especially in the presence of marked anhedonia, social isolation, psychotic symptoms, or multiple treatment failures.
Prompt clinical management, continuity of care, and treatment personalization are the keys to effective management and a favorable prognosis.
The diagnosis of a major depressive episode requires careful assessment because depressive symptoms may occur in many other pathological contexts. Careful clinical differentiation is therefore essential to exclude conditions that may mimic a major depressive episode but require different therapeutic approaches.
1. Normal bereavement: grief after the loss of a loved one may cause profound sadness, insomnia, and loss of appetite. However, in normal bereavement:
2. Depressive episode in bipolar disorder: the presentation may be indistinguishable from unipolar depression. A previous manic episode defines bipolar I disorder; the combination of a hypomanic episode and a major depressive episode, in the absence of mania, defines bipolar II disorder. Mixed features alone are not equivalent to a bipolar diagnosis.
3. Anxiety disorders and somatoform disorders: chronic anxiety may cause fatigue, insomnia, cognitive difficulties, and social withdrawal. Somatoform disorders, particularly somatic symptom disorders, may also mimic depression; however, in these cases the clinical focus is on physical symptoms, which are often multiple and persist despite medical investigation.
4. Neurocognitive disorders: depression and a neurocognitive disorder may mimic each other or coexist. Cognitive deficits associated with depression may improve with treatment, but are not necessarily reversible and do not exclude underlying neurodegenerative disease.
5. General medical conditions: endocrine, neurological, inflammatory or neoplastic diseases may contribute to depressive symptoms. Somatic signs and response to antidepressants do not reliably distinguish the origin; investigations must be targeted according to history, physical examination and risk factors.
6. Medications and substances: some medications and substances may cause or worsen depressive symptoms, but risk is not uniform across entire classes such as beta blockers or contraceptives. Temporal relationship, dose, vulnerability, alcohol and substance use or withdrawal, and alternative diagnoses must be assessed.
A major depressive episode is a complex disorder with multifaceted clinical manifestations and intricate neurobiological underpinnings. It requires a careful, multidimensional assessment that includes the clinical history, the presence of risk factors, exclusion of concomitant medical conditions, and correct differentiation from other forms of psychopathological distress.
Optimal management requires early diagnosis, empathic and structured care, and the use of integrated, personalized therapeutic strategies capable of reducing the risk of chronicity, disability, and suicide.