Chronic fatigue syndrome and depression have distinct biological features, researchers in Canada report, suggesting that the two conditions have unique causes.

Unlike patients with depression, those with chronic fatigue syndrome have lower skin conductance levels and higher skin temperatures in the arms and legs.

These measurements may offer a way to distinguish chronic fatigue syndrome from depression, Dr. Hannah Pazderka-Robinson and her colleagues suggest in their report, published in the International Journal of Psychophysiology.

The considerable overlap in the symptoms of chronic fatigue syndrome and of depression has led many to question whether chronic fatigue syndrome is really a different condition, or if it is actually a manifestation of depression.

Dr. Pazderka-Robinson and her team at the University of Alberta, Edmonton, theorized that psychological and physical indicators could be used to discriminate between the two.

The researchers obtained data from 36 nondepressed subjects with chronic fatigue syndrome, 19 with depression and 33 normal, healthy controls.

Electrical conduction activity in the skin was measured using electrodes placed on the third and fourth fingers of each hand. Skin temperatures were measured using temperature transducers placed on the fifth finger.

The researchers found that skin temperatures differed significantly in the chronic fatigue syndrome group and the depression group and the control group, with average temperatures of 34.1, 31.1, and 30.1 degrees Centigrade, respectively.

In contrast, the average skin conductance levels were significantly lower in the chronic fatigue syndrome group compared with the control group and the depression group. The depression group and the control group did not differ significantly from each other with regard to this measurement, however.

There are “measurable differences” between patients with chronic fatigue syndrome and depression, the researchers conclude. These findings add to a “growing body of evidence” of physiologic differences between the two conditions and suggest different causes.

SOURCE: International Journal of Psychophysiology, August 2004.