Differential diagnoses

In: Diagnosis

To confer major depressive disorder as the most likely diagnosis, other potential diagnoses must be considered, including dysthymia, adjustment disorder with depressed mood or bipolar disorder. Dysthymia is a chronic, milder mood disturbance in which a person reports a low mood almost daily over a span of at least two years. The symptoms are not as severe as those for major depression, although people with dysthymia are vulnerable to secondary episodes of major depression (sometimes referred to as double depression). Adjustment disorder with depressed mood is a mood disturbance appearing as a psychological response to an identifiable event or stressor, in which the resulting emotional or behavioral symptoms are significant but do not meet the criteria for a major depressive episode. Bipolar disorder, also known as manic–depressive disorder, is a condition in which depressive phases alternate with periods of mania or hypomania. Although depression is currently categorized as a separate disorder, there is ongoing debate because individuals diagnosed with major depression often experience some hypomanic symptoms, indicating a mood disorder continuum.

Other disorders need to be ruled out before diagnosing major depressive disorder. They include depressions due to physical illness, medications, and substance abuse. Depression due to physical illness is diagnosed as a mood disorder due to a general medical condition. This condition is determined based on history, laboratory findings, or physical examination. When the depression is caused by a substance abused including a drug of abuse, a medication, or exposure to a toxin, it is then diagnosed as a substance-induced mood disorder. In such cases, a substance is judged to be etiologically related to the mood disturbance.

Schizoaffective disorder is different from major depressive disorder with psychotic features because in the schizoaffective disorder at least two weeks of delusions or hallucinations must occur in the absence of prominent mood symptoms.

Depressive symptoms may be identified during schizophrenia, delusional disorder, and psychotic disorder not otherwise specified, and in such cases those symptoms are considered associated features of these disorders, therefore, a separate diagnosis is not deemed necessary unless the depressive symptoms meet full criteria for a major depressive episode. In that case, a diagnosis of depressive disorder not otherwise specified may be made as well as a diagnosis of schizophrenia.

Some cognitive symptoms of dementia such as disorientation, apathy, difficulty concentrating and memory loss may get confused with a major depressive episode in major depressive disorder. They are especially difficult to determine in elderly patients. In such cases, the premorbid state of the patient may be helpful to differentiate both disorders. In the case of dementia, there tends to be a premorbid history of declining cognitive function. In the case of a major depressive disorder patients tend to exhibit a relatively normal premorbid state and abrupt cognitive decline associated with the depression.