The diagnostic criteria for a major depressive episode are:
Sorting things out between major depression and adjustment disorder with depressed mood can be challenging and often the latter diagnosis wins out. However, if a patient has a history of depressive episodes, then the former diagnosis would be ahead.
Other disorders, such as delirium (particularly hypoactive delirium), dementia, substance use, anxiety, schizophrenia, somatoform and personality disorders can at times mimic the presentation of a depressive episode. Because the treatment of each is rather different, it is important to spend time eliciting a good history.
Many medical and neurological disorders can lead to secondary depression, as can many medications (e.g., chloramphenicol, trimethopriom, clofazimine, griseofulvin). The list is long, so consider diagnoses and medications carefully.
★It is important to differentiate depression from dementia as their treatment is very different. Thus a patient with depression who presents with what is commonly referred to as pseudo-dementia, would benefit more from an antidepressant than a cognitive enhancer. A table to help differentiate between dementia and depression is provided here.
Points to consider in diagnosing depression in the medically ill
----In reference to the last point, Irv Yalom reportedly once said "A patient can have every reason in the world to be depressed, but that doesn't mean he won't benefit from an antidepressant."