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Diagnosing Depression

Question:

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p>I’ve read about SPECT tests used in the diagnosis of depression, besides the mental examination of course. How reliable are they? Why aren’t they widely used yet? Are there any other reliable physical examinations or brain imaging techniques that could verify that someone is depressed? And how can I trust a diagnosis that is solely based on a conversation, no matter how long and/or extensive it is and even after ruling out other causes through physical examinations?

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Answer:

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p>Excellent questions all. Before I attempt to answer them, let’s start by describing what SPECT is, for the benefit of people who might not know. SPECT stands for “single photon emission computed tomography”, and it is a form of functional brain scanning. Traditional brain scans (or body scans) take a picture of the body or brain like a still image. They show how the part of the body inside the body look; whether there are injuries, lesions, breaks or scars or other physical problems. Examples of traditional scan technologies include X-rays, CT scans, and MRIs (where “CT” stands for computed tomography). X-rays and CT scans (which use X-rays) are good for examining bones but not so good for softer tissues. MRI, which uses a powerful magnet to make pictures, is the technology of choice for examining soft tissue like the brain.

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p>In recent years, functional scanning has become possible. Functional scanning allows doctors to take a movie of the body or brain in action so as to see how the body or brain operates in real time. SPECT, and two sister technologies (fMRI and PET) allow a window into how the brain functions in real-time. These technologies make it possible to take still or moving images of how blood flows in the brain (more or less) and this helps doctors to know what parts of the brain are most active at any given moment. Years of research have helped doctors to understand which parts of the brain are responsible for what parts of human behavior. Therefore, the ability to see what parts of the brain light up while a person is thinking about different things helps doctors to know whether various brain parts are acting typically or not. For instance, certain parts of the brain (the frontal and prefrontal areas) are important for attention and concentration. When these areas are working properly, people are able to concentrate. When they are not working properly, people have difficulty concentrating. You can see differences of this sort in a SPECT/fMRI/PET study by asking someone to concentrate or not and looking at what parts of their brain light up and how intensely they light up. More or less. The science is not exactly exact yet. This sort of functional imaging is a very very recent development and the full extent of how this technology will impact psychiatry and psychology is only just being developed.

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p>One promise of SPECT and similar technologies is that a single (or several) patterns of brain activation will emerge from the literature which mark the presence of depression. This is to say, one day it may be possible to get into a scanner and to have your own brain’s patterns correlated with normative patterns developed from studies of depressed people. A goodness of fit test will be done, and if your brain pattern is close enough to the depressed people’s patterns, then you might be said to be depressed. I’d be shocked if this sort of thing happened anytime soon, however. Depression is a very heterogeneous problem – it seems to result from multiple causes, both physical and mental in nature, and to present itself in a variety of patterns and profiles. You can be depressed and agitated or depressed and melancholy and it is still depression for instance. You can cure depression with medicine or with psychotherapy and both methods work just about as well as one another. For these and other reasons, I seriously doubt that anyone will come up with a “depression” detector any time soon.

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p>You ask if there are any other physical tests that definitively mark depression and the answer is no. The best doctors have ever come up with is something I believe was called the dexamethasone suppression test (if memory serves). Suppression test results were only weakly related to depression diagnosis, however, and thus the test was never widely used as a diagnostic tool.

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p>While SPECT and related technologies might not be so useful just yet as diagnostic indicators for depression, this is not to say that they don’t yield good information. Functional imaging is brilliant at showing how patterns of brain activity change over time. I do not doubt for a second that as a depressed person becomes less depressed that their brain activity patterns will change as well. Functional imaging techniques may thus one day be useful means of tracking the progress of therapy for depression. That is if the price comes way down. The machines are very expensive and mostly used for research these days. I’m sure that diagnostic functional imaging would be thousands of dollars at this point. Also – the information that would be yielded from such a study, while unique, would not be necessary in order to successfully treat depression. You simply don’t need to know that a specific area of the brain is light up or not lighting up to know that someone is depressed and might benefit from psychotherapy or medication.

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p>You ask how you can trust a diagnosis that is based on a conversation instead of a physical finding and that is an excellent question. This is actually a philosophical question in disguise. The question assumes that there is a such a thing as a physical reality separate from a mental reality, I think. That may be the case so far as the physical world is concerned, but when it comes to human beings, our mental and physical realities are hopelessly muddled. There is no definitive physical signature that says when someone is depressed but depression exists nevertheless. So does the experience of pain, by the way, which also cannot be definitively linked to a physical finding. Pain can and does exist in the absence of discernible injury.

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p>The fact is, I’ll bet you make decisions about the existence or absence of things all the time without making sure that a physical test is performed every time. Have you ever gotten behind the wheel of a car after having a drink at a restaurant, reasonably confident that you won’t be guilty of drinking and driving when you pull away? If so – you’ve made a diagnosis (hopefully a good one) with real-world consequences on a conversational basis and in the absence of physical facts. Doctors are very good at examining behavior and drawing conclusions; this is what they do for a living. Many of the conditions they may be called upon to treat may in fact have no discernible physical basis (or may have no physical basis at all). If you feel the need to hold out for purely physical measures of human experience that is your choice, but you’ll be holding out there for a long time before it will become practical to do so.

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