If somebody has a treatment refractory depression at a young age with cognitive deficits that go beyond what is normal for major depression is it appropriate to seek a thorough medical workup? If so, what tests should be done, and what specialists should be seen?
Before doing tests, the history should be explored to determine if the deficits are new or old. The most common pre-existing problem in a young person would be childhood onset learning disorders, the causes of which are never really known to us.
A person may never have been diagnosed with one before and might have been able to compensate fairly well, but the chronic depression could then make it that much harder to function with these pre-existing problems.
In terms of more recent deficits, substance abuse should first be ruled out. Second, an inadvertant cause of new deficits could be medication treatment itself. Multiple psychiatric medications are often used in treatment-resistnat disorders, in combinations that can cause cognitive impairment.
Sometimes careful reduction or elimination of ineffective medication can lead to improved clarity of thinking. If the deficts seem to have begun only in early adulthood, there are really very few medical illnesses that one could look for beyond the effects of depression itself.
Thyroid disease (more common) or vitamin B12 deficiency (less common) are easy to test for. Rarer chronic neurological illnesses such as multiple sclerosis might be considered but would almost always present with other, more obvious symptoms.
There is also a remote possibility of a brain tumor or other structural disease of the central nervous system, which should be ruled out with neuroimaging in patients who are not responding to antidepressants and have significant cognitive problems.
In terms of how to proceed with the evaluation, the first step would be blood tests for thyroid disease and general medical screens (kidney, liver, blood counts, vitamin B12 levels), ordered by the psychiatrist. Often be a neuropsychological assessment, using pencil-and-paper tests, can better define the nature of the cognitive problem, and whether it is new or old.
A general physical exam by an internist, and a neurological consultation to determine the best type of brain imaging, are logical steps as well.