Patients with chronic pain disorders, such as fibromyalgia, appear to have abnormalities in the self-monitoring mechanism that allows the discrimination of internally produced versus externally produced stimuli, new research shows.

The findings, which appear in Psychosomatic Medicine, are based on a study of 20 patients with a chronic pain disorder (including 10 with fibromyalgia),10 with schizophrenia, and 10 normal controls.

The subjects were asked to rate a tactile sensation to the hands that was either self-produced by the patient moving the hand, or produced externally by an experimenter.

In normal subjects, the sensation from self-produced stimuli was rated as less intense than the sensation from the same externally produced stimuli, lead author Dr. Matthias Karst, from Hannover Medical School in Germany, and colleagues note.

In contrast, patients in the other groups rated these sensations as being comparable, the investigators point out. Further analysis showed that this observation was largely confined to patients with a chronic pain disorder.

“This is the first study of the self-monitoring in patients with chronic widespread pain,” the researchers state.

The results suggest that chronic pain disorders “interfere with the correct function of the self-monitoring mechanism that normally allows us to distinguish self-produced from externally produced tactile stimuli.”

SOURCE: Psychosomatic Medicine, January/February 2005.