See the “Differential Diagnosis” section for Major Depressive Episode. A history of a Manic, Mixed, or Hypomanic Episode precludes the diagnosis of Major Depressive Disorder. The presence of Hypomanic Episodes (without any history of Manic Episodes) indicates a diagnosis of Bipolar II Disorder. The presence of Manic or Mixed Episodes (with or without Hypomanic Episodes) indicates a diagnosis of Bipolar I Disorder.
Major Depressive Episodes in Major Depressive Disorder must be distinguished from a Mood Disorder Due to a General Medical Condition. The diagnosis is Mood Disorder Due to a General Medical Condition if the mood disturbance is judged to be the direct physiological consequence of a specific general medical condition (e.g., multiple sclerosis, stroke, hypothyroidism). This determination is based on the history, laboratory findings, or physical examination. If it is judged that the depressive symptoms are not the direct physiological consequence of the general medical condition, then the primary Mood Disorder is recorded on Axis I (e.g., Major Depressive Disorder) and the general medical condition is recorded on Axis III (e.g., myocardial infarction). This would be the case, for example, if the Major Depressive Episode is considered to be the psychological consequence of having the general medical condition or if there is no etiological relationship between the Major Depressive Episode and the general medical condition.
A Substance-Induced Mood Disorder is distinguished from Major Depressive Episodes in Major Depressive Disorder by the fact that a substance (e.g., a drug of abuse, a medication, or exposure to a toxin) is judged to be etiologically related to the mood disturbance. For example, depressed mood that occurs only in the context of withdrawal from cocaine would be diagnosed as Cocaine-Induced Mood Disorder, With Depressive Features, With Onset During Withdrawal.
Dysthymic Disorder and Major Depressive Disorder are differentiated based on severity, chronicity, and persistence. In Major Depressive Disorder, the depressed mood must be present for most of the day, nearly every day, for a period of at least 2 weeks, whereas Dysthymic Disorder must be present for more days than not over a period of at least 2 years. The differential diagnosis between Dysthymic Disorder and Major Depressive Disorder is made particularly difficult by the fact that the two disorders share similar symptoms and that the differences between them in onset, duration, persistence, and severity are not easy to evaluate retrospectively. Usually Major Depressive Disorder consists of one or more discrete Major Depressive Episodes that can be distinguished from the person’s usual functioning, whereas Dysthymic Disorder is characterized by chronic, less severe depressive symptoms that have been present for many years. If the initial onset of chronic depressive symptoms is of sufficient severity and number to meet criteria for a Major Depressive Episode, the diagnosis would be Major Depressive Disorder, Chronic (if the criteria are still met), or Major Depressive Disorder, In Partial Remission (if the criteria are no longer met). The diagnosis of Dysthymic Disorder is made following Major Depressive Disorder only if the Dysthymic Disorder was established prior to the first Major Depressive Episode (i.e., no Major Depressive Episodes during the first 2 years of dysthymic symptoms), or if there has been a full remission of the Major Depressive Episode (i.e., lasting at least 2 months) before the onset of the Dysthymic Disorder.
Schizoaffective Disorder differs from Major Depressive Disorder, With Psychotic Features, by the requirement that in Schizoaffective Disorder there must be at least 2 weeks of delusions or hallucinations occurring in the absence of prominent mood symptoms. Depressive symptoms may be present during Schizophrenia, Delusional Disorder, and Psychotic Disorder Not Otherwise Specified. Most commonly, such depressive symptoms can be considered associated features of these disorders and do not merit a separate diagnosis. However, when the depressive symptoms meet full criteria for a Major Depressive Episode (or are of particular clinical significance), a diagnosis of Depressive Disorder Not Otherwise Specified may be made in addition to the diagnosis of Schizophrenia, Delusional Disorder, or Psychotic Disorder Not Otherwise Specified. Schizophrenia, Catatonic Type, may be difficult to distinguish from Major Depressive Disorder, With Catatonic Features. Prior history or family history may be helpful in making this distinction.
In elderly individuals, it is often difficult to determine whether cognitive symptoms (e.g., disorientation, apathy, difficulty concentrating, memory loss) are better accounted for by a dementia or by a Major Depressive Episode in Major Depressive Disorder. This differential diagnosis may be informed by a thorough general medical evaluation and consideration of the onset of the disturbance, temporal sequencing of depressive and cognitive symptoms, course of illness, and treatment response. The premorbid state of the individual may help to differentiate a Major Depressive Disorder from dementia. In dementia, there is usually a premorbid history of declining cognitive function, whereas the individual with Major Depressive Disorder is much more likely to have a relatively normal premorbid state and abrupt cognitive decline associated with the depression.