Subtyping of MDD
The current subtyping of MDD is based on severity, cross-sec-tional features and course features.
The rating of severity is based on a clinical judgment of the number of criteria present, the severity of the symptomatology, and the degree of functional distress. The ratings of current severity are classified as mild, moderate, severe without psychotic features, severe with psychotic features, in partial remission, or in full remission. The definition of “mild” refers to a episode results in only mild impairment in occupational or psychosocial functioning or mild disability. “Moderate” implies a level of severity which is intermediate between mild and severe and is associated with moderate impairment in psychosocial functioning. The definition of “severe” describes an episode which meets several symptoms in excess of those required to make a diagnosis of major depressive episode and is associated with marked impairment in occupational or psychosocial functioning and definite disability characterized by inability to work or perform basic social functions. Severe with psychotic features indicates the presence of delusions or hallucinations which occur in the context of the major depressive episode. The categories of mood-congruent versus mood-incongruent psychotic features are made in thecontext of a psychotic depressive disorder. When the content of delusions or hallucinations is consistent with depressive themes, mood-congruent psychotic diagnosis is made. When the psychotic features are not related to depressive themes or include symptoms such as thought insertion, broadcast, or withdrawal, the modifier of mood-incongruent psychotic features is used. A recent review has suggested that mood-incongruent psychosis in MDD is associated with a poorer prognosis. For depression with psychotic features, whether they are mood-congruent or mood-incongruent, antipsychotic medication in combination with antidepressant medication or electroconvulsive therapy (ECT) is required to treat the disorder.
Partial remission indicates that the episode no longer meets full criteria for major depressive episode but that some symp-toms are still present or the period of remission has been less than 2 months. In full remission, the individual has no significant symptoms of depression for a period of at least 2 months.
The assessment of cross-sectional features involves the presence or absence of catatonic, melancholic, or atypical features dur-ing an episode of depression. The specifier with catatonic fea-tures is used when profound psychomotor retardation, prominent mutism, echolalia, echopraxia, or stupor dominate the clinical picture. The presentation of catatonia requires a differential di-agnosis which includes schizophrenia, catatonic type, bipolar I disorder, catatonic disorder due to a general medical condition, medication-induced movement disorder leading to catatonic fea-tures, or neuroleptic malignant syndrome.
The specifier with melancholic features is applied when the depressive episode is characterized by profound loss of in-terest or pleasure in activities and lack of reactivity to external events as well as usual pleasurable stimuli. In addition, at least three of the following melancholic features must be present: de-pression is typically worse in the morning, early morning awak-ening, psychomotor change with marked retardation or agitation, significant weight loss, or profound and excessive guilt. MDD with melancholic features is particularly important to diagnose because of the prediction that it is more likely to respond to so-matic treatment including electroconvulsive therapy. Individuals with melancholic features experience more recurrence of MDD. The findings of hypercortisolism following dexamethasone as well as reduced REM latency is associated with the melancholic subtype of MDD.
Finally, the category of MDD with atypical features was previously called “atypical depression”. This syndrome is char-acterized by prominent mood reactivity in which there is exces-sive responsiveness of mood to external events and at least two of the following associated features: increased appetite or weight gain, hypersomnia, leaden paralysis (a feeling of profound aner-gia or heavy feeling) and interpersonal hypersensitivity (rejec-tion sensitivity). Depressive episodes with atypical features are also common in individuals with bipolar I or II disorder as well as seasonal affective disorder.
MDD is diagnosed with certain course features such as post-partum onset, seasonal pattern, recurrent, chronic, and with or without full interepisode recovery. Depression with onset in the postpartum period has been the subject of increasing attentionin psychiatric consultation to obstetrics and gynecology. The presence of a MDD may occur from 2 weeks to 12 months af-ter delivery, beyond the usual duration of postpartum “blues” (3–7 days). Postpartum blues are brief episodes of labile mood and tearfulness which occur in 50 to 80% of women within 5 days of delivery. However, depression is seen in 10 to 20% of women after childbirth (Miller, 2002), which is higher than rates of depression found in matched controls. There is greater vulner-ability in women with prior episodes of major mood disorder par-ticularly bipolar disorder, and there is a high risk of recurrence with subsequent deliveries after an MDD with postpartum onset. The postpartum onset episodes can present either with or without psychosis. Postpartum psychotic episodes occur in 0.1 to 0.2% of deliveries. Depression in postpartum psychosis is associated with prominent guilt and may involve individuals with a prior history of bipolar I disorder. If an episode of postpartum psy-chosis occurs, there is a high risk of recurrence with subsequent deliveries. Heightened attention to identification of postpartum episodes is required because of potential risk of morbidity and mortality to mother and newborn child.
The specifier with seasonal pattern is diagnosed when epi-sodes of MDD occur regularly in fall and winter seasons and sub-sequently remit during spring and summer. When the pattern of onset and remission occurs for the last 2 years, one diagnoses an MDD with seasonal pattern. Often, this pattern is characterized by atypical features including low energy, hypersomnia, weight gain and carbohydrate craving. Although the predominant pattern is fall–winter depression, a minority of individuals show the re-verse seasonal pattern with spring–summer depression. Specific forms of light therapy with 2500 lux exposure has been shown to be effective in MDD with seasonal pattern. Because seasonal depression has clinical features which are similar to atypical fea-tures, the risk of a possible bipolar II disorder must be considered since atypical features are more common in depressive episodes occurring as part of bipolar II. These individuals when exposed to antidepressant medication or bright light therapy may evolve a switch into hypomanic or manic episode.
Clinical and scientific attention to the course of MDD fo-cuses upon the depiction of longitudinal course. Life charting of MDD involves the use of several course specifiers. Each episode is denoted with or without full recovery. MDD manifests either a single or recurrent pattern of episodes. Remission of depression requires a 2-month interval in which the criteria are not met for a major depressive episode. The specifier chronic MDD involves the persistence of a major depressive episode continually, satisfy-ing full MDD criteria for at least 2 years.