Associated descriptive features and mental disorders. Individuals with a Major Depressive Episode frequently present with tearfulness, irritability, brooding, obsessive rumination, anxiety, phobias, excessive worry over physical health, and complaints of pain (e.g., headaches or joint, abdominal, or other pains). During a Major Depressive Episode, some individuals have Panic Attacks that occur in a pattern that meets criteria for Panic Disorder. In children, separation anxiety may occur. Some individuals note difficulty in intimate relationships, less satisfying social interactions, or difficulties in sexual functioning (e.g., anorgasmia in women or erectile dysfunction in men). There may be marital problems (e.g., divorce), occupational problems (e.g., loss of job), academic problems (e.g., truancy, school failure), Alcohol or Other Substance Abuse, or increased utilization of medical services. The most serious consequence of a Major Depressive Episode is attempted or completed suicide. Suicide risk is especially high for individuals with psychotic features, a history of previous suicide attempts, a family history of completed suicides, or concurrent substance use. There may also be an increased rate of premature death from general medical conditions. Major Depressive Episodes often follow psychosocial stressors (e.g., the death of a loved one, marital separation, divorce). Childbirth may precipitate a Major Depressive Episode, in which case the specifier With Postpartum Onset is note.
Associated laboratory findings. No laboratory findings that are diagnostic of a Major Depressive Episode have been identified. However, a variety of laboratory findings have been noted to be abnormal more often in groups of individuals with Major Depressive Episodes compared with control subjects. It appears that the same laboratory abnormalities are associated with a Major Depressive Episode regardless of whether the episode is part of a Major Depressive, Bipolar I, or Bipolar II Disorder. Most laboratory abnormalities are state dependent (i.e., affected by the presence or absence of depressive symptoms), but some findings may precede the onset of the episode or persist after its remission. Laboratory tests are more likely to be abnormal in episodes with melancholic or psychotic features and in more severely depressed individuals.
Sleep EEG abnormalities may be evident in 40%-60% of outpatients and in up to 90% of inpatients with a Major Depressive Episode. The most frequently associated polysomnographic findings include 1) sleep continuity disturbances, such as prolonged sleep latency, increased intermittent wakefulness, and early morning awakening; 2) reduced non-rapid eye movement (NREM) stages 3 and 4 sleep (slow-wave sleep), with a shift in slow-wave activity away from the first NREM period; 3) decreased rapid eye movement (REM) latency (i.e., shortened duration of the first NREM period); 4) increased phasic REM activity (i.e., the number of actual eye movements during REM); and 5) increased duration of REM sleep early in the night. There is evidence that these sleep abnormalities may persist after clinical remission or precede the onset of the initial Major Depressive Episode among those at high risk for a Mood Disorder (e.g., first-degree family members of individuals with Major Depressive Disorder).
The pathophysiology of a Major Depressive Episode may involve a dysregulation of a number of neurotransmitter systems, including the serotonin, norepinephrine, dopamine, acetylcholine, and gamma-aminobutyric acid systems. There is also evidence of alterations of several neuropeptides, including corticotropin-releasing hormone. In some depressed individuals, hormonal disturbances have been observed, including elevated glucocorticoid secretion (e.g., elevated urinary free cortisol levels or dexamethasone nonsuppression of plasma cortisol) and blunted growth hormone, thyroid-stimulating hormone, and prolactin responses to various challenge tests. Functional brain imaging studies document alterations in cerebral blood flow and metabolism in some individuals, including increased blood flow in limbic and paralimbic regions and decreased blood flow in the lateral prefrontal cortex. Depression beginning in late life is associated with alterations in brain structure, including periventricular vascular changes. None of these changes are present in all individuals in a Major Depressive Episode, however, nor is any particular disturbance specific to depression.