Tuesday, June 14, 2005

Gulf War Syndrome, Revisited;
Relationship Between Pain and Depression

Sooner or later, I had to get back to science.  I'm even going to try to avoid putting any political slant in this post...

Recently, an article was published about the health effects of military service in the <Persian|Arabian> Gulf.  The authors found that the most significant elevation in risk was for the risk of developing fibromyalgia and chronic fatigue syndrome.  A bit earlier, an article appeared that described the relationship between depression and pain in patients with fibromyalgia. In this post, I show how the results of these two studies

After the first US war in the Gulf, some veterans reported various somatic problems that came to be known, collectively, as Gulf War Syndrome.  This was controversial right from the start, because the symptoms often were nonspecific, and there were no consistent abnormalities found on physical exam or laboratory studies.  Some physicians were convinced that there was some kind of problem.  In fact, there is a group at the University of Michigan Health System that has been studying this.  There's another group at the Washington University (St. Louis) School of Medicine.  (The WUSTL group does not appear to have a web page.)

Led by Seth Eisen, MD, the WUSTL group found (Web MD article, journal abstract) that these veterans have an increased risk of skin rashes, indigestion, fibromyalgia, and chronic fatigue syndrome.  No one has been able to determine exactly what factor or factors cause the increased risks.  The absolute numbers were small, but the relative risks were significantly elevated.  Vets who had deployed to the Gulf War were 2 times more likely to have fibromyalgia, and 40 times more likely to have chronic fatigue syndrome (CFS), compared to contemporaneous vets who did not serve in the region.  The study was not designed to detect problems that occurred earlier, but which had resolved prior to the study.  

Fibromyalgia and CFS used to be controversial, but now both are generally accepted to be serious, definable problems.  The reasons for the controversy were similar to the reasons  that Gulf War Syndrome was controversial.   It turns out that patients with nonspecific symptoms and minimal findings on physical exam or on laboratory testing often are dismissed, perhaps even marginalized.  In some cases, though, it is possible to find indications of distinct pathology.  

A good example of this comes from the UM group, led by Danial Clauw, MD, published in the journal Arthritis & Rheumatism.  They did various kinds of sensory testing as well as functional MRI (fMRI, brain imaging.)  They studied patients with  fibromyalgia, with varying level of depressive symptoms.  There is a statistical association between depression and fibromyalgia, but many people have one without the other.  

In the study, they measured two components of pain: sensory, and affective.  The sensory dimension of pain is the intensity of the sensation itself; the affective dimension is the intensity of the emotional response to the pain.  It turns out that fMRI can localize each dimension of pain in different brain areas.  This makes it possible to see if the level of depression is correlated with the severity of each of the two dimensions of pain, using subjective measures (patient ratings) and objective measures (fMRI.)

The results indicated that the level of depression did correlate with the affective dimension of pain, on both the subjective and the objective tests.  However, there was no relationship between the level of depression and the sensory dimension of pain.  

Physicians and others who have studied pain have long made a distinction between the two dimensions of pain, based upon clinical observation.  The UM study, however, provides a nice way to show that there are distinct brain pathways for each.  It also shows that it is not realistic to attribute the pain experienced in fibromyalgia to depression.  Together, the two studies indicate that there is at least some truth to at least some of the claims about Gulf War syndrome, and that at least some of the problems these vets experience cannot be attributed to depression.

category: medicine
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