Research — 27 October 2015

To determine whether or not a patient suffers from depression, a doctor will often refer to a checklist of symptoms found in the Diagnostic and Statistical Manual of Mental Disorders (DSM), often called the “bible” of psychiatry. According to the current protocol, it does not matter which of the symptoms the patients have, as long as they have a certain number of them.

A new study shows that this may not be the most accurate way to diagnose depression, however, as some of these symptoms play a much bigger role than others in driving depression, and that the symptoms listed in DSM may not be the most useful ones.

“We need to stop thinking of depression as a disease that causes a number of interchangeable symptoms”, says lead author Dr. Eiko Fried from the Katholieke Universiteit (KU) Leuven Faculty of Psychology and Educational Sciences in Belgium. “Depression is a complex, extremely heterogeneous system of interacting symptoms. And some of these symptoms may be far more important than others”.

For the study, researchers analyzed data on 28 symptoms provided by 3,463 participants with depression. They then examined the connections between these symptoms. Their network analysis shows that some symptoms are more “central,” or more connected, than others. As a result, these symptoms carry much more weight toward the depressive process.

“If you think of depression as a network of interacting symptoms, one symptom can cause another,” Fried says. “For instance, insomnia may lead to fatigue, which in turn may cause concentration problems that feed back into insomnia. This example of a vicious circle shows that the specific symptoms patients report, and their interactions, can be of crucial clinical importance”.

“Depression is not like, say, measles. When you have measles, your symptoms help the doctor figure out what underlying disease you have. But once you are diagnosed, it doesn’t really matter which of the possible symptoms you did or didn’t get. Treating the disease itself makes all your symptoms disappear.”

“Depression is more complicated. It is not an infection or a specific brain disease. There is no easy cure, no drug that makes all symptoms go away. Instead, we may want to focus treatment efforts on the symptoms driving a patient’s depression,” says Fried.

In the study, the two main DSM symptoms – sad mood and decreased interest or pleasure — ranked among the top five in terms of centrality. But the researchers also found that DSM symptoms such as hypersomnia (feeling sleepy throughout the day), agitation, and weight change are not more central than other common depression symptoms such as pessimism and anxiety.

 “Ideally, the list of depression symptoms should become more comprehensive to do justice to the heterogeneity of depression. I also think both clinicians and researchers can learn a lot from paying more attention to individual symptoms and their interactions. But of course, we need much more research before we can actually replace the DSM diagnosis of depression with something else,” says Fried.
This article first appeared on ‘Psych Central’ on 25 October 2015.


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